Nuclear Science and Technology

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ISSN 1810-5408
Nuclear Science
and Technology
Volume 3, Number 2, June 2013
Published by
VIETNAM ATOMIC ENERGY SOCIETY
NUCLEAR SCIENCE AND TECHNOLOGY
Volume 3, Number 2, June 2013
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KHOA HỌC VÀ CÔNG NGHỆ HẠT NHÂN
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Nuclear Science and Technology, Vol. 3, No. 2 (2013), pp. 1-6
Studies of multiparticle photonuclear reactions in natural iron
induced by 2.5 GeV bremsstrahlung
Pham Duc Khue*, Kim Tien Thanh, Nguyen Thi Hien
Institute of Physics, VAST, 10 Dao Tan, Ba Dinh, Hanoi, Vietnam
*
(Received 27 June 2013, accepted 26 September 2013)
Abstract: Multiparticle photonuclear reactions produced on natural iron target with maximum endpoint energy of 2.5 GeV bremsstrahlung have been investigated by using the activation method in
combination with -ray spectrometric techniques. The -spectra were measured with a high energy
resolution -spectrometer based on HPGe detector. The radioactive residual nuclei formed via nuclear
reactions were identified based on their half-lives and -ray energies. The yields of reaction products
were determined based on their -activities. In order to improve the accuracy of the experimental
results a series of -spectra were measured at different cooling times and the necessary corrections
were made. More than twenties radioactive nuclei formed via the following photonuclear reactions:
nat
Fe(,xn), natFe(,xnyp) and natFe(,-xn) have been identified and their yields have been determined.
The present experimental results are compared with reference data and analyzed with an empirical
formula given by Rudstam.
Keywords: Bremsstrahlung; Activation method; Gamma spectrometer, Reaction yield.
I. INTRODUCTION
The photonuclear reactions with high
energy bremsstrahlung photons generated
from the electron linear accelerators (linac)
have been the subject of many investigations.
The photon interacts with nuclei in different
ways depending on the photon energy. When
high energy photons interact with the target
nuclei a number of radioactive products are
induced as a result of different reaction
mechanisms such as (1) giant dipole resonance
(GDR) in the energy region from about 10
MeV to 30 MeV, (2) quasi-deuteron resonance
(QDR) from about 30 MeV to 140 MeV and
intranuclear cascade and evaporation at energy
greater than 140 MeV. Generally, the possible
photonuclear reactions can be classified into
four groups, namely simple reactions;
spallation
reactions;
fission;
and
fragmentation. The knowledge of the reaction
channels and yields of the reaction products
from the de-excitation of the nuclei can help in
understanding the interaction process [1-4].
Recently, with the fast development of high
energy electron accelerators the studies of
photospallation reactions for light, medium
and heavy weight targets have been made at
energies up to 5 GeV [4-11].
The aim of the present work is to
investigate the multiparticle photonuclear
reactions on medium iron target nuclei
bombarded by 2.5 GeV bremsstrahlung. The
main attentions were to identify the reaction
products and to determine the reaction yields.
The obtained yields are analyzed by means of
Rudstam' five parameters formula.
The experiment work was carried out at
the 2.5 GeV electron linac of the Pohang
Accelerator Laboratory (PAL), POSTECH,
Pohang, Korea.
II. EXPERIMENTAL
The experiment was carried out at the 10o
beam line of the 2.5 GeV electron linac of the
PAL. The details of the 2.5 GeV electron linac
and its applications were described elsewhere
[12]. The bremsstrahlung photons were
©2013 Vietnam Atomic Energy Society and Vietnam Atomic Energy Institute
STUDIES OF MULTIPARTICLE PHOTONUCLEAR REACTIONS IN …
where  is the detection efficiency, an
represents the fitting parameters, and E is the
energy of the photopeak, E0 = 1 keV. The
detection efficiencies as a function of the
photon energy measured at different distances
between the source and the surface of the
detector were illustrated in ref. [13].
produced when a pulsed electron beam hit a
thin W target with a size of 50 mm  50 mm
and a thickness of 0.2 mm. The W target is
located at 38.5 cm from the beam exit
window.
In this work, the high purity (99.559%)
natural iron foil made by Reactor Experiments
Inc. (USA), in disc shape with diameter of 1/2
inch and thickness of 0.05 inch was used. The
activation foil was placed in air at 24 cm from
the W bremsstrahlung target and they were
positioned at zero degree with the direction of
the electron beam. The irradiation time was 4
hours. During the irradiation, the electron
linac was operated with a repetition rate of 10
Hz, a pulse width of 1 ns, and the electron
energy of 2.5 GeV with total electron beam
current of 2.19 × 1014 electrons.
For the measurements, the cooling and the
measuring times were chosen based on the
activity and the half-life of each radioactive
isotope considered. In order to optimize the
dead time losses and the coincidence summing
effect we have also chosen the appropriate
distance between the foil sample and the
detector for each measurement. Generally, the
dead times were kept below 1.0 % during the
measurement. Typical -ray spectra from the
irradiated iron foil taken at different waiting
time were shown in Fig. 1 and Fig. 2. The
energy values of the -rays were taken from
ref. [14].
After an irradiation and an appropriate
waiting time, the irradiated iron foil was taken
off, and then the induced gamma activities of
III. DATA ANALYSIS AND RESULTS
the irradiated foil were measured by using
a gamma spectrometer. The gamma
The nuclear reaction products were
identified based on their half-lives and gamma
ray energies. In this work, total of 27
radioactive nuclei were measured, such as
53
Fe, 52Fe, 56Mn, 54Mn, 52mMn, 52gMn, 51Cr,
49
Cr, 48Cr, 48V, 48Sc, 47Sc, 46Sc, 44mSc, 44gSc
43
Sc, 45K, 43K, 42K, 41Ar, 39Cl, 3S8Cl, 34mCl,
24
Na, 22Na, 55Co and 56Co. These isotopes were
formed from the different channels such as
multineutron emission reactions natFe(,xn);
photospallation reactions natFe(, xnyp) and
photopion reactions natFe(,xn-), where x and
y being the number of neutrons and protons
emitted. Obviously, the photospallation
reaction was the most dominant competitive
channel among others. The maximum number
of neutrons and protons emitted from the
spallation reaction 58Fe(,21n15p) 22Na were
21 and 15. Two products 55Co and 55Co were
produced in the photopion reactions. Some
reaction products are in isomeric state (52mMn,
44m
Sc and 34mCl).
spectrometer used for the measurements was a
coaxial CANBERRA high-purity germanium
(HPGe) detector with a diameter of 59.2 mm
and length of 30 mm. The HPGe detector was
coupled to a computer-based multichannel
analyzer card system, which could determine
the photopeak-area of the gamma ray spectra
by using the GENIE2000 (Canberra) computer
program. The energy resolution of the detector
was 1.80 keV full width at half maximum
(FWHM) at the 1332.5 keV peak of 60Co. The
photopeak efficiency curve of the gamma
spectrometer was calibrated with a set of
standard gamma sources such as 241Am, 137Cs,
54
Mn, 22Na, 60Co, 133Ba and 152Eu. The
measured detection efficiencies were fitted by
using the following function:
5
ln    a n ln E / E0 
n
(1)
n 0
2
PHAM DUC KHUE, KIM TIEN THANH, NGUYEN THI HIEN
Fig. 1. Typical gamma-ray spectrum from natural Fe irradiated with 2.5 GeV bremsstrahlung
with ti= 240 min, td = 40 min and tc = 10 min.
Fig. 2. Typical gamma-ray spectrum from natural Fe irradiated with 2.5 GeV bremsstrahlung
with ti= 240 min, td = 8395 min and tc = 120 min.
where N0 is the number of the target atoms, 
is the absolute photopeak efficiency, I is the
gamma ray intensity, f is the correction factor,
 is the decay constant of the product nucleus,
 is pulse width, ti is the irradiation time, tw is
the waiting time, tc is the counting time, T is
cycle period,  is the flux of the photon beam,
 is the reaction cross section, Eth the
By considering the pulse nature of the
bremsstrahlung beam, the photopeak area or
the number of detected gamma rays, C, can be
expressed as follows:
C
N0I f (1  e )(1  eti )et w (1  et c )
 (1  e T )

E m ax
E th
 ( E ) ( E )dE
(2)
3
threshold reaction energy, and Emax the
maximum bremsstrahlung energy.
characteristic only for spallation. Meanwhile
yield of the products from the natFe(,xn) and
nat
Fe(,-xn) nuclear reactions can not be
described by the Rudstam’s formula.
For any nuclear reaction, the yield is
given by [10]:
Y  No 
E m ax
E th
(E)(E)dE
We plot the yield data of natFe irradiated
with 2.5 GeV bremsstrahlung obtained in this
work together with those data obtained by G.
Kumbartzki et al., [6] at 1.5 GeV
bremsstrahlung in Fig. 4, and it is shown that
the present yields are in good agrement with
most of the reference data.
(3)
On basis of the equations (2) and (3),
the experimental yield can be derived from the
measured activity, C, as follows:
Y
C(1  e  T )
I  f (1  e  )(1  e t i )e t d (1  e t m )
(4)
The main sources of the errors are due to
statistical
error,
detection
efficiency,
photopeak area determination, coincidence
summing effect and nuclear data used. In
order to improve the accuracy of the
experimental results, corrections for -ray
interferences, self-absorption of -rays and
coincidence summing effect were taken into
account. The total uncertainties were
estimated to be 5 - 10%.
The measured yield was obtained by
averaging over several measurements. In the
present work, the reaction yields were
determined relative to that of 54Mn where the
yield of 54Mn is normalized to unity. The
obtained data were analyzed by using the
Rudstam’s formula as follows [3-6]:
(A, Z) 
3/ 2
ˆ PR 2 / 3
exp[ PA  R Z  SA  TA2 ] (5)
PAt
1.79(e  1)
where: (Z,A) is the cross section for the
production of the residual nucleus with charge
Z and mass number A; At is mass number of
target; P, R, S, T and ˆ are free parameters
with P  6.08  At0.89 =0.1695, R  11.8 At0.45
=1.93, S=0.485; T=0.00032, At = 55.845,
max
ˆ  (0.81  0.192 ln E max
)A1t.13 = 65.213, E

IV. CONCLUSION
Multiparticle photonuclear reactions on
Fe induced by 2.5 GeV bremsstrahlung have
been investigated by using the activation
method. Total of 27 radioactive nuclides with
half-lives ranging from 8.51 min (53Fe) to
2.6109 yr (22Na) have been found. Most of the
reaction products identified were formed via
the spallation reactions, and their yields can be
described by empirical Rudstam’s formula.
The agreement between the measured and
predicted yields for the photospallation
reactions is quite satisfactory. The obtained
data have yielded valuable information not
only for the understanding of reaction
mechanisms and testing the validity of the
nuclear model, but also for the application to
other field such as astrophysics, shielding
physics,
activation
analysis,
isotope
production and transmutation of nuclear
wastes.
nat
= 2500 MeV.
The yields for the natFe(,xn) reactions can
be approximated by the following formula
[15]:
(, xn )  0.058A0t.684 exp[ 37A t 0.864(x 1)5 / 4 ] (6)
Rudstam’s five parameter formula is
based on the evaporation model and
experimental data. It allows one to represent
the mass distributions of the residual nuclei in
an analytical form. The experimental and
calculated yields were plotted against the mass
number of the product nuclei and shown in
Fig. 3. As can be seen, our experimental yields
are well consistent with the prediction values.
The yield distribution curves seem to be
4
PHAM DUC KHUE, KIM TIEN THANH, NGUYEN THI HIEN
Relative Yield
100
10
nat
Sc
K
Ar
Cl
Na
calculation
Co
Fe
Mn
Cr
V
1
Fe(,xnyp)
Cr
Mn
Fe
V
Sc
0.1
Ar
Cl
0.01
K
Na
Co
1E-3
20
25
30
35
40
45
50
55
60
Mass number , A
Fig. 3. Mass distribution of radioactive nuclei produced in natFe irradiated with 2.5 GeV bremsstrahlung.
The curves were calculated by Rudstam's formula.
10
Relative Yield
This wor k (2.5 GeV)
Ref. [6] (1.5 GeV)
1
0.1
0.01
1E-3
20
25
30
35
40
45
50
55
60
Mass number , A
Fig.4. Realative yields of radioactive nuclei produced in natFe induced by 2.5 GeV ()
and 1.5 GeV () bremsstralung photons.
ACKNOWLEDGMENTS
completion of this experiment. This work is
also supported in part by the Vietnam National
Foundation for Science and Technology
Development (NAFOSTED) under grant
number 103.04-2012.21.
The authors are very grateful to Prof.
Nguyen Van Do for his encourage and
support. We would like to thanks to the
Pohang Accelerator Laboratory, POSTECH,
Korea for the invitation and support during the
5
Young Seok Lee, Youngdo Oh, Hee-Seock
Lee, Moo-Hyun Cho, In Soo Ko and Won
Namkung, “Isomeric cross-section ratios for
45
nat
the
Sc(,n)44m,gSc,
Ti(,xn1p)44m,gSc,
nat
44m,g
nat
Fe(,xn5p)
Sc and
Cu(,xn8p)44m,gSc
reactions
induced
by
2.5
GeV
Bremsstrahlung”, Nucl. Instr. and Meth.,
B266, 5080 (2008).
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spallation reactions”, Nucl. Phys. A 126, 401
(1969).
[2] J. R.Wu and C.C. Chang, “Pre-equilibrium
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Phys. Rev. C 16, 1812 (1977).
[3] K. Lindgren and G. G. Jonsson, “Photoninduced nuclear reaction above 1 GeV”, Nucl.
Phys., A197, 71(1972).
[11] Nguyen Van Do, Pham Duc Khue, Kim Tien
Thanh and Nguyen Thi Thanh Van, “High
energy photon induced nuclear reactions in
natural copper”, Comm. in Phys., Special
issue, 19,177 (2009).
[4] A.S. Danagulyan, N.A.Demekhina and G.A.
Vartapetyan, “Photonuclear reactions in
medium weight nuclei 51V, 55Mn and Cu”,
Nucl. Phys. A 285, 482 (1977).
[12] H. S. Lee, S. Ban, T. Sato, K. Shin, J. S. Bak,
C. W. Chung, H. D. Choi, “Photoneutron
Spectra from Thin Targets Bombarded with
2.0 GeV Electrons”, J. Nucl. Sci. and Tech.
Supplement 1, 207 (2000).
[5] S. Shibata, M. Imamura, T. Miyachi and M.
Mutou, “Photonuclear spallation reactions in
Cu”, Phys. Rev. C 35, 254 (1987).
[6] G. Kumbartzki and U. Kim, “High-energy
photonuclear reactions in vanadium and iron”,
Nucl. Phys. A 176, 23 (1971).
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Tran, Van Duan Phung, Y. Seok Lee, HeeSeock Lee, Moo-Hyun Cho, In Soo Ko and
Won Namkung, A.K.M. Moinul Haque
Meaze, K Devan and Guinyun Kim.
“Measurement of Neutron and Photon
Distributions by Using an Activation
Technique at the Pohang Neutron Facility”. J.
Korean Phys. Soc., 48, 382 (2006).
[7] T. Sato, K. Shin, S.Ban, Y. Namoto,
H.Nakamura, H.Hirayama, “Measurements of
high – energy photonuclear reaction yields in
the 2.5 GeV electron beam stop”, Nucl. Instr.
and Meth. A 401, 476 (1997).
[8] Hiromitsu Haba, “Recoil Studies of
photonuclear reactions at intermediate
energies”, J. Nucl. Radiochem. Sci. 3, 11
(2002).
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Radioactive Isotopes”, Version 2.1, January
2004, web: http://ie.lbl.gov/toi.html.
[15] M. L. Terranova and O.A.P.Tavares, “Total
Nuclear Photoabsorption Cross Section in the
Range 0.2-1.0 GeV for Nuclei throughout the
Periodic Table”, Phys. Scri. 49, 267 (1994).
[9] Koh Sakamoto, “Radiochemical study on
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[10] Nguyen Van Do, Pham Duc Khue and Kim
Tien Thanh, Le Truong Son, Guinyum Kim,
6
Analysis of steam generator tube rupture accident
for Korean reactor APR1400
Le Dai Dien* and Le Tri Dan
Nuclear Safety Center - Institute for Nuclear Science and Technology
179 Hoang Quoc Viet, Cau Giay, Ha Noi
*
(Received 1 July 2013, accepted 23 July 2013)
Abstract: The APR1400 is an advanced light water reactor designed by KEPCO, Korea. Steam
generator tube rupture (SGTR) is one of the design basic accidents (DBA) which needs to be analyzed
in safety analysis report.
In this paper, a steam generator tube rupture event was simulated by using RELAP/SCDASIM
system code and some results are compared with MARS code with modeled MULTID
components of the reactor vessel and two steam generators. Further simulations for tube rupture
depend on the broken positions and number of ruptured tubes is also estimated. The results are in
fairly good agreement with one simulated by MARS code.
Keywords: APR1400, steam generator tube rupture, safety analysis report, direct vessel injection,
reactor trip, reactor coolant pump trip, nodalization.
I. INTRODUCTION
The APR1400 is an advanced light water
reactor designed by KEPCO, Korea. The next
design developed from experienced OPR-1000
adopted new safety features such as a safety
injection system with a direct vessel injection
(DVI) and a passive fluidic device in the
safety injection tank (SIT). The reactor has a
capacity of 4,000 MWth with a 2 x 4 loop
arrangement of the reactor coolant system
(RCS). The APR1400 has been designed
based on System 80+ from CE and now
Westinghouse. With only two steam
generators with one hot and two cold legs is a
distinguish feature of this design. This feature
of design is also used in AP1000. The plant
also has 60 years of a design lifetime. Two
units are under construction in Korea and
other is also under construction in UAE.
For the safety analysis report, there have
been many investigations on DBA for
APR1400. The SSAR (Standard Safety
Analysis Report) recently has been submitted
to US NRC in the attemp to have the license.
For the thermal hyfraulic safety analysis,
KAERI had developed MARS code [8] to
simulate the NPP system based on RELAP5.
Multi-dimensional components including
reactor core and SGs had been installed in the
MARS code. In this report, a steam generator
tube rupture (SGTR) event was simulated by
using RELAP/SCDASIM [1] and some results
are compared with one from MARS with
modeled MULTID component of the reactor
vessel and two steam generators.
In the operation of nuclear power plant,
SGTR may occur spontaneously or by another
reason. Tube degradation mechanisms such as
coolant stress corrosion cracking, outside
stress corrosion cracking, inter-granular
attack,
intergranular
stress
corrosion
cracking,fretting, wear, thinning, corrosion,
erosion, fatigue or cavitation result in the
spontaneous tube ruptures. From the safety
point of view, a SGTR event is an important
safety concern in a nuclear power plant. It
results in a loss of the pressure boundary
ANALYSIS OF STEAM GENERATOR TUBE RUPTURE ACCIDENT FOR …
between the primary and second systems. If
there is any broken tube of a steam generator,
high pressure primary coolant will leak into
the secondary side of the steam generator
which allows the radioactive inventory to
turbine building and then radiation leakage is
unavoidable.
control system automatically terminates main
feedwater following a reactor trip with
reduced primary coolant temperatures.
In the framework of the cooperation
project between KAERI and VAEI [2],
researchers of the Nuclear Safety Center at the
Institute for Nuclear Science and Technology
(INST) have been actively participated in the
safety analysis of fundamental DBAs for
APR1400 under assisstance of experienced
experts of Thermal Hydraulics Safety
Research Divison (THSR) of KAERI. Several
results were presented in the Ninth National
Conference on Nuclear Science and
Technology and reported in domestic Nuclear
Science and Technology journal [3], [4], [5].
For SGTR, APR1400 design features are
capable of avoiding containment bypass
during the event: The steam bypass control
system is automated and provides a path to
remove steam from the SGs when MSIV
closed. In the event of SGTR, The steam
bypass control system will automatically
relieve secondary pressure and dump steam to
the condenser. The N-16 monitor is attached
in each steam generator to assist in the
diagnosis of the event and the main feedwater
Table I. Steam Generator Parameters of APR1400 [6]
Parameter
Value
Number of units
Heat transfer rate per SG, (kcal/h)
Number of Tubes per SG
Average Active Tube Length per SG (m)
Heat Transfer Area per SG, (m2)
2
1.721 x 109
13,102
19.391
15,205
Primary Side:
Design pressure/temperature (kg/cm2/0C)
Coolant inlet temperature, (0C)
Coolant outlet temperature (0C)
Coolant flow rate, each, (kg/h)
Coolant volume each, (m3)
Tube size, OD, (mm)
Tube thickness, nominal, (mm)
Primary inlet nozzle, No./ID, (mm)
Primary outlet nozzle, No./ID, (mm)
175.76/343.33
323.88
290.55
37.78 x 106
86.84
19.05
1.0668
1/1066.8
2/762
Secondary Side:
Design pressure/temperature (kg/cm2 /0C)
Steam pressure, (kg/cm2)
Steam flowrate per SG, (kg/h)
Feedwater temperature at full power, (0C)
Steam nozzle, No./ID, (mm)
84.36/298.88
70.30
4.070 x 106
232.22
2 / 711.2
8
LE DAI DIEN, LE TRI DAN
Fig. 1. Steam Generator of APR1400 [6]
assumed to be operating in an automatic mode
and no operator action is taken into account
during the transient.
II. MODELING DESCRIPTION
The steam generator parameters are
presented in Table I and general schematic is
in Fig. 1. The data for steam generator are
referenced form SSAR of APR1400 [6].
The hydrodynamic systems are composed
of four parts: the reactor pressure vessel,
reactor coolant transport system, steam
generator and main steam line. The reactor
vessel consists of a fuel region with hotest fuel
assembly and the other FAs which makes an
active core, core-bypass, core support,
downcomer, upper plenum and lower plenum.
The reactor coolant system with four cold legs
and two hot legs, four RCPs plus PZR in one
of the hot leg is simulated. The secondary
parts of the steam generator are modeled by
combined two main steam line for each SG as
one as seen in nodalization. The steady state
calculations are often used to start the
transient simulations and already reported in
[2] and earlier reports ([3], [4], [5]).
Fig. 2 shows the nodalization scheme of
APR1400 which used by safety analysis in the
cooperation project. The main nuclear steam
supply system components like a reactor
pressure vessel (RPV), steam generators (SG),
hot legs, cold legs, reactor coolant pumps
(RCP), a pressurizer (PZR) are modeled. The
important safety systems like high pressure
injection safety (HPIS), low pressure injection
safety (LPIS), accumulators or safety injection
tanks (SIT) are also modeled.
The control systems include the reactor
protection trip, reactor coolant pump trip, the
pressurizer safety valves and so on. The
reactor systems and safety systems are
9
Fig. 2. Nodalization diagram of APR1400 NPP for safety analysis by RELAP/SCDAPSIM
Fig. 3. System pressure in SGTR event simulated by MARS [7, 8] (Left) and RELAP/SCDAPSIM (right)
10
III. CALCULATION RESULTS AND
DISCUSSION
PRZ backup heater is actuated as designed.
However, the pressure in reactor coolant
system continues decreasing which leads to
reactor trip. The reactor trip results in a safety
injection at 1360s at 12.47 MPa (compared
with 1462s calcualted in [8]). After the reactor
trip, the main steam isolation valves (MSIVs)
are closed, the pressure in the secondary side
increases due to an evaporation of the water in
the shell side and the water coolant in the tube
side. The main steam line safety valves
(MSSVs) will be opened when the secondary
pressure exceeds a setpoint.
A. SGTR scenario with 1 broken tube and
comparison with MARS code.
According to the control parameters for
APR1400 [7], in the transient if the primary
RCS pressure decreases lower than 15.17 MPa
the heaters in PZR will be actuated. However,
if the pressure still decreases and reaches a
set-point of 12.47 MPa, a high-pressure
injection safety (HPIS) system is started to
inject water into the reactor core. The SITs are
designed to automatically start an injection
when the PZR pressure is lower than 4.03
MPa. The set-point of the reactor trip signal is
the same as the SI set-point.
At the first time period, from 0s to 1360s,
the water level in PZR decreases because of
the leakage of reactor coolant into the
secondary side. After the ECCS is actuated,
water level in PZR increases again. The water
levels in PZR and in both steam generators
(intact and broken) are shown in Fig. 4. At the
time 1360s, the water level in both Steam
generator decrease rapidly due to the steam
continue generate while the feed water pump
and reactor coolant pump were tripped
following the reactor trip. Due to the
shutdown of the reactor and the actuation of
ECCS, the steam generated in the secondary
side of steam generator decreases and the
water level rises again.
The operating pressure of RCS is 15.5
MPa and SG secondary side is 7 MPa.
Therefore, when the SGTR event occurs, highpressure primary coolant will leak into the
secondary side through the break during the
event.
Fig. 3 shows the primary and secodary
system pressures during the simulation for the
SGTR event. When a steam generator tube is
ruptured, the reactor coolant system pressure
immediately drops as a tube break and the
Fig. 4. Water level in Steam generator and Pressurizer by MARS [7, 8] (Left)
and ELAP/SCDAPSIM (right)
11
Fig. 5. Mass flow rate in steam generator by MARS [7, 8] (Left) and RELAP/SCDAPSIM (right)
The mass flow rates in SGs from feed
water line, economizers are presented in Fig 5.
The flow rates of the steam generators still
remain until the reactor trip. After the reactor
trip, the flow rate of the steam generator
decrease quickly due to the reactor coolant
pump tripped and feed water pump is closed
following the reactor trip.
reason may be MULTID is used in MARS.
The other reason for the difference in
comparison is that it is not clear which part of
a steam generator tube is assumed to rupture
for SGTR analyses in [7, 8].
The main feed water flow supplied from
economizer (90% of total feed water as
design) fluctuated as seen in Fig. 5 and so the
water levels also fluctuated as in Fig. 4. This
is explained by the fluctuation of pressure in
shell side during the SGTR in which the
coolant leakage from primary to the secondary
side. It should be noted that the time for
simulation is taken from 0 incase of
RELAP/SCDAPSIM while it is taken as
continuation from steady state in MARS.
The secondary-side pressure is regulated
by the control systems when it increases due
to tube rupture that results in the leakage of
the primary coolant. As described above, the
main safety isolation valves (MSIVs) are
automatically actuated as turbine trip and
steam will bypass to the condenser system. If
the primary coolant leak rate through the
broken tube exceeds the maximum capacity of
the steam bypass control system, the secondary
side SG level starts to increase, and finally a highlevel signal is generated to close the MSIVs and
the pressures in broken SG as well as intact SG
increase as seen in Fig. 4. As reactor trip the main
feed water line is also closed.
Fig. 5 shows the flow rate of feed water
before and after the event. There are
differences
in
results
simulated
by
RELAP/SCDAPSIM and MARS, the main
Fig. 6. Pressure vs time with different break position.
12
study should be performed in the future
works. The experience of SGTR analysis,
which is a design basis event, provides the
understanding and knowledge bases for
transient scenario development and experience
in the review of safety analysis report for
chapter 15 (safety analysis).
REFERENCES
Fig. 7. Pressure changes in reactor coolant system
during the events with different number of broken
tubes (from 1 to 10 respectively)
B. SGTR – Multiple broken tubes.
The effect of tube rupture location has
been investigated for APR1400 [10] for
multiple steam generator tube rupture
(MSGTR). In this preliminary study, these are
only simulated draftly. The time events,
especially the pressure drop occurs depend on
the location of rupture. In case of rupture at
the top of U-Tube bundle, the primary side
pressure drops ealier than the rupture at down
side as seen in Fig. 6.
For the multiple SGTR, the Fig. 7
illustrates primary pressure behavior during
the event with different number of broken
tubes. The larger number of broken tubes is,
the ealier and higher the pressure drop is
expected.
IV. CONCLUSION
Analyses of postulated steam generator
tube rupture events in an APR1400 nuclear
power plant have been carried out using a
best-estimate
system
analysis
code
RELAP/SCDAPSIM.
The
fundamental
difference between simulations by another
computer codes is in leak rate. This may be
resulted from various causes such as
modelling of rupture and discharge
coefficients. The other differences have been
noted in this study. However, a sensitivity
[1] C. M. Allison and R.J. Wagner,
RELAP/SCDAPSIM/MOD3.2 (am+) Input
Manual, Supplemental, Innovative Systems
Software, LLC, Dec. 2001.
[2] Le Van Hong et al. Summary Report on
Cooperation project between KAERI and
VAEI: Study on Safety Analysis of PWR
reactor core in Transient and Accident
Conditions (2009-2010).
[3] Le Đai Dien, Hoang Minh Giang, Le Van
Hong, Le Thi Thu, Nguyen Thi Tu Oanh,
Vo Thi Huong, Phạm Tuan Nam, Nguyen
Thanh Thuy, Some preliminary results of
LOCA problem for Korean Reactor
APR1400. The Ninth National Conference
on Nuclear Science and Technology, Ninh
Thuan, 18-19 August 2011.
[4] Le Đai Dien et al. Loss of Coolant Accident
Analysis of APR1400 Reactor. Nuclear
Science and Engineering, No.2 June 2011.
[5] Nguyen Thi Thanh Thuy, Le Dai Dien and
Hoang minh Giang. Feed Water Line Break
(FWLB) Analysis for APR1400 Reactor
Using RELAP5. The Ninth National
Conference on Nuclear Science and
Technology, Ninh Thuan, 18-19 August
2011.
[6] APR1400 SSAR. Chapter 5: Reactor
Coolant System and Connected Systems.
[7] Chung B.D., et al, 2005, “Development and
assessment of multi-dimensional flow
models in the thermal-hydraulic system
analysis code MARS,” KAERI/TR3011/2005, KAERI.
[8] MARS CODE MANUAL, VOLUME IV:
Developmental
Assessment
Report.
KAERI/TR-3042/2005.
13
[9] Ji Hwan Jeong et al. Best Estimate Analysis
of MSTGR event in APR1400 Aiming to
Examine the Effect of Affected Steam.
[12] Ji Hwan Jeong et al. Effects of tube rupture
modeling and the parameters on the analysis
of multiple steam generator tube rupture
event progression in APR1400. Nuclear
Engineering and Design 224 (2003).
[10] Generator Selection. Journal of KNS,
Vol.33, No.4, August 2002.
[13] A. Auvinen et al. Steam generator tube
ruptures (SGTR) scenarios. Nuclear
Engineering and Design 235 (2005).
[11] Ji Hwan Jeong et al. The effect of tube
rupture location on the consequences of
multiple steam generator tube rupture event.
Annals of Nuclear Energy 29 (2002).
14
Design and simulation calculations for one - and two - neutron
transfer 24Si(p,d)23Si and 24Si(p,t)22Si reaction experiment
N.T. Khai1, B.D. Linh1, L.X. Chung1, D.T. Khoa1, A. Obertelli2, A. Corsi2,
A. Gillibert2, N. Alamanos2, D. Sohler3, Zs. Dombradi3, N. Keeley4
1
2
Institute for Nuclear Science and Technology (INST), VINATOM, Vietnam
Institut de Recherche sur les Lois fondamentales de l’Univers (IRFU), CEA, France
3
Institute of Nuclear Research ATOMKI, Hungary
4
National Center for Nuclear Research (NCNR), Poland
Abstract: Magic numbers are well established for stable nuclei: 2, 8, 20, 28, 50, 82, 126 but are known
not to be valid for unstable neutron-rich and proton-rich nuclei located far from the β-stability region.
Normally, structural research for these nuclei is performed based on inverse-kinematics nuclear
reaction experiment with secondary radioactive isotope beams produced by the cyclotron facility. In
this work we would like to report on the design and simulation calculations for an experiment on
producing proton-rich isotopes 22-23Si based on one- and two-neutron transfer reactions of (p,d) and
(p,t) types with 42 MeV/nucleon incident 24Si beam from the accelerator facility SPIRAL2 at
GANIL, France. The obtained results are included: (i) optimization design for experimental
configuration in inverse kinematics, (ii) tracking of beam trajectory with detectors CATS1&2, (iii)
particle identification with MUST2 telescope system, (iv) identification for g.s and 2+ excited states,
and (v) count statistics evaluation and reconstruction for nuclear excitation spectra.
The main purposes of the experiment are to measure the energies of the neutron single particle
and hole states in 23Si from 24Si(p,d) reaction to deduce the strength of the N=8 shell closure, and
populate the excited states of the expected doubly-magic nucleus 22Si from 24Si(p,t) reaction to check
the stability of the N=14 shell closure.
Keywords: one- and two-neutron transfe, inverse kinematics, particle identification, beam trajector.
I. PHYSICS MOTIVATION
Atomic nuclei are few-body systems,
mainly governed by the strong interaction
force and quantum mechanical laws leading to
a shell structure for the nucleons. In nuclear
structure shell closure and shell gaps are a
direct consequence of the nucleon-nucleon
interaction. Magic nuclei, with a magic
number of protons and neutrons, are spherical
and more inert than their neighbors since their
excitation requires more energy to scatter
nucleons above the energy gap to reach the
next shell. Magic numbers are well established
for stable nuclei: 2, 8, 20, 28, 50, 82, 126 but
are known not to be universal over the nuclear
chart. The study of unstable nuclei including
the neutron-rich and proton-rich ones located
far from the stability valley is the only way to
establish the structure of nuclei throughout the
nuclear chart and unravel the isospin
properties of the nuclear force. New shell
closures can be reordered and are predicted in
regions which may be difficult to explore, due
to the limit in the current experimental setups
and to the beam intensities. More specifically,
the N=20 and N=28 shell gaps are known to
vanish for neutron-rich nuclei but these
phenomena still need further investigation [1].
In even-even nuclei, the excitation energy of
the first excited 2+ state is very sensitive to the
shell structure above the Fermi level. Large 2+
DESIGN AND SIMULATION CALCULATIONS FOR ONE - AND TWO - NEUTRON …
state excitation energies directly correspond to
large energy shell gaps. 22Si is the mirror
nucleus of 22O, recently suggested to be a new
doubly-magic nucleus away from stability [24]. We therefore expect the extremely proton
rich nucleus 22Si to be one of the very few
unstable doubly-magic nuclei. 22Si differs
from its mirror nucleus by the Coulomb
energy difference, which makes a pair of
protons nearly unbound (S2p~0) in 22Si.
23
Si is a very asymmetric nucleus with 14
protons and 9 neutrons lying next to the
presumably doubly closed shell nucleus 22Si.
The energy of its excited states gives
information on the neutron single particle
states. The single-particle states in 23Si are
sensitive to the N=14 d5/2–s1/2 and N=16
s1/2-d3/2 shell gaps [5], whereas hole states
are excitations across the p-sd shell gap
responsible for the N=8 magic feature. Single
particle transfer reactions are the most
adequate tools to get this kind of information.
We propose an experiment on accessing
the proton-rich isotopes 22-23Si via 1n and 2n
removal reactions by using a 24Si beam to
impinge on Hydrogen target. In the
24
Si(p,t)22Si process a pair of neutrons will be
picked up. The cross section of the
24
Si(p,t)22Si direct reaction is predicted to be
smaller than that of the 24Si(p,d)23Si one,
where only one neutron is picked up. The
coupled reaction channels (CRC) calculations
by considering the coupling to the (p,d)
channel give a cross section of 0.57 mb to
populate the ground state of 22Si and a cross
section of 0.26 mb to populate the first excited
2+ state [6].
In the proposed experiment we focus on
the spectroscopy of single-particle states in
23
Si and the possibility of populating the first
excited (2+) state in 22Si from 2n removal
reactions. The question of spectroscopic
factors obtained from deeply-bound nucleon
removal will also be addressed.
In this report we would like to present the
design and simulation calculations for the
experimental research on structure of the
proton-rich nuclei 22-23Si based on the 1n and
2n transfer reactions of 24Si(p,d)23Si and
24
Si(p,t)22Si in inverse kinematics, where the
42 MeV/nucleon incident 24Si beam is
produced as a secondary one by the
accelerator facility SPIRAL2 at GANIL. The
aims
of
the
experiment
are
to:
Fig.1. View of experimental setup for measurement of the 1n and 2n removal reactions from 24Si beam
using 5 MUST2 telescope configuration.
16
NGUYEN TUAN KHAI et al.
(i) measure the energies of the neutron
single particle and hole states in 23Si from oneneutron transfer 24Si(p,d)23Si reaction to
deduce the strength of the N=8 shell closure,
two detectors CATS1&2 to the reaction target
are, respectively, 1600 and 500 mm. This
allows us to determine the position of the
beam particle hitting the target. It is assumed
that the reaction of interest occurs randomly in
the target, the energy losses of the beam
particles and reaction products have to be
taken into account. It should be noticed that
the reaction kinematics, i.e. energy and
scattering angle, are calculated based on the
model-calculated angular distribution.
(ii) populate the excited states of the
expected doubly-magic nucleus 22Si from
24
Si(p,t)22Si two-neutron transfer reaction to
check the stability of the N=14 shell closure,
(iii) search for possible deviations of
spectroscopic factor values for a nucleus
having a large neutron to proton binding
energy asymmetry,
In order to compensate the low incidentbeam intensity, we plan to use the GANIL
solid H2 target [9] with a 1 mm thickness (7
mg/cm2). The target diameter is 10 mm. It has
already been successfully used in a previous
experiment [10]. It is the first time this target
will be used with MUST2 detector [11]. LISE
simulations give a beam size of 5 mm FWHM
on the target. In any case, the stopping of
beam particles in the copper target structure
will not harm the experiment nor perturb the
measurement.
(iv) test of the setup to see if the (p,p2n)
reaction can be used as a tool to study the
proton unbound state in nuclei close to the
proton drip line.
The experiment will be performed by the
missing mass technique to detect recoil particles
from the (p,d), (p,t) and (p,p2n) channels.
II. EXPERIMENTAL CONFIGURATION
AND SIMULATION CALCULATIONS
In the proposed experiment a secondary
beam of 24Si will be produced by
fragmentation of a primary 32S beam at energy
of 95 MeV/nucleon, with an intensity of 4
eμA. The beam will be then purified at 99%
with the LISE spectrometer and the associated
Wien filter. Residual contaminants will be
eliminated via time of flight. Beam production
and measurements in this mass region have
been performed for experiment E398 [7] and
LISE++ predictions have been found to be
reliable.
The low beam intensity allows
considering a very efficient MUST2
configuration composed of five detectors: one
at 0 degree and four side detectors. The zerodegree detector is located at 240 mm from the
target. It will be used both for projectile-like
fragments (trigger condition) and target-like
recoils, i.e. recoiling light changed particles.
The side detectors cover an angular range
from 15 to 24.5 degrees from the center of the
target (Fig.1). Such a design of the target –
MUST2 detector configuration is assured to
be consistent with volume of the target
chamber and cover kinematic range of the
(p,d) and (p,t) transfer reactions of interest.
The MUST2 detector has been conceived to
handle multi-detection in a single detector and
be efficient for correlation studies. This is a
modular array consisting of 6 large area
Fig. 1 shows the designed configuration
of the experimental setup, where the 24Si beam
are produced at 300 pps intensity and 42
MeV/nucleon energy. The beam trajectory
tracking is performed by two multi-wire
proportional chambers (MWPC) CATS1&2
[8] for position measurement. Distances from
17
silicon strip-Si(Li)-CsI telescopes with
associated electronics and data acquisition
system. The detector has been designed to
identify the recoiling light charged particle
through time of flight, energy loss and energy
measurements and to determine precisely their
scattering angle through X, Y position
measurements. The mechanics of the
telescopes is a truncated pyramid with a base
130x130 mm2 and an “active” face of
110x110 mm2. The first stage of the telescopes
consists in a 100x100 mm2 double sided Sistrip array detector with 128 horizontal and
128 vertical strips. The strip thickness is 300
μm. Such a structure of the detector yields a
position resolution of 0.7x0.7 mm2. The
overall energy and time resolutions are 50 keV
and 250 ps for alphas of 5.48 MeV, and a 300
keV energy threshold for protons [11]. Protons
of less than 6 MeV stop in the strip detector
and are identified by energy vs. time of flight
measurement. The second stage is a lithium
drifted silicon diode Si(Li) of 4.5 mm
thickness with an energy resolution of 120
keV for alphas of 5.48 MeV [11]. Above 6
MeV and up to 32 MeV protons traverse the
strip detector and stop in the Si(Li) detector. For
applications where high energy particles must be
detected, such as protons with energies above 32
MeV and up to 80 MeV, the telescopes are
equipped with a third stage made with CsI
crystal of 3 cm thickness with an energy
resolution of 6% for alphas of 5.48 MeV [11].
Based on the determined kinematical
characteristics the identification of light
charged particles will be performed via
correlation between energy loss (ΔE) in the Si
strips and absorbed energy (E) in the CsI
stage. Fig. 2-left shows an unambiguous
identification for proton, deuteron and triton
produced from the reactions 24Si(p,p’),
24
Si(p,d)23Si and 24Si(p,t)22Si, respectively. For
the scattering 24Si(p,p’) [12] most of the
recoiling protons are out of coverage of the
MUST2 configuration.
E(MeV/nucleon)
E(MeV/)
ΔECsI (MeV)
E(MeV/)
g.s (23Si)
p
d
t
ΔESi-Strip (MeV)
22
2
+
Si
g.s
θ (deg)
Fig. 2. - (Left) Particle identification based on energy loss correlation on Si-strip and CsI
stages of the MUST2 telescopes.
- (Right) Energy-scattering angle correlation for recoiling light particles:
Sum of measured deuterons and tritons from 24Si(p,d)23Si and 24Si(p,t)22Si measured by all the
5 MUST2 detectors. The three kinematic lines correspond to the population of the (i) ground
state of 23Si, (ii) the ground state of 22Si and (iii) the 2+ excited state of 22Si at tentative
excitation energy of 3.2 MeV.
18
NGUYEN TUAN KHAI et al.
The kinematics of the neutron transfer
channels should be measured with differential
cross sections down to 0 degree in the centerof-mass. Fig. 2-right shows the simulation
results on energy - scattering angle correlation
for deuterons and tritons from the neutron
transfer reactions 24Si(p,d)23Si and 24Si(p,t)22Si
measured by all the 5 MUST2 detectors. The
obtained kinetic lines are used to identify not
only for the reaction channels, but also for the
ground state and the 2+ excited state of 22Si.
We expect this measurement to allow a very
precise DWBA (Distorted wave Born
approximation) or CDCC (Continuum
Discretized Coupled Channels) analysis and
SF (spectroscopic factor) extraction. The
projectiles going through the target and
projectile-like reaction products will be
stopped and identified in the zero-degree
MUST2 telescope.
allowing an angular distribution for
spectroscopic factor extraction. Few hundred of
counts are also expected in the population of
each p-shell hole states. This statistics allows
determining the transferred angular momentum
during the (p, d) reaction and address the
quantum numbers to the populated states.
C. Count statistics for (p, t) channel:
The cross sections to populate the ground
state and the first 2+ state of 22Si from (p, t)
reaction are estimated at 0.57 mb and 0.26 mb,
respectively, via the CRC calculation [6].
With 5 days of beam time, it gives a final
number of counts in the excitation energy
spectrum of about 300 counts for the ground
state and 120 counts for the 2+ state from the
detection of tritons. Fig. 3 shows a
reconstruction for the excitation energy
spectrum of about 300 counts for the ground
state and 120 counts for the 2+ state from the
detection of tritons. Fig. 3 shows a
reconstruction for the excitation energy
spectrum of 22Si based on the proposed
experimental configuration and relativistic
kinematic calculations, where the first 2+ state
is assumed at 3.2 MeV [4]. The spectral result
shows a good separation between the ground
state and the 2+ excited state.
III. BEAM TIME REQUEST AND COUNT
STATISTICS ESTIMATION
A. Beam time request
B. Count statistics for (p,d) channel:
For the (p,d) channel the 1n transfer cross
section of 16.8 mb to populate the ground
state of 23Si has been calculated via DWBA
considering the Kooning-Delaroche nucleusnucleon optical potential valid for energies up
to 200 MeV/nucleon [6]. For the proposed
configuration of the experiment the
acceptance of about 60% and the MUST2
efficiency of 90% have been simulated. For a
5-day beam time, the statistics of about 1800
counts will be measured for the ground state,
Count
E(MeV/)
For this experiment we request five days
of beam time plus an additional one day for
calibration and electronics tuning with the 32S
primary beam downscaled at few 104 pps
(screened MUST2 detector at zero-degree) at
50 MeV/nucleon energy.
Energy (MeV)
Fig. 3. Simulated excitation spectrum with
g.s and 2+ state at 3.2 MeV of 22Si. The Gaussian
fit gives the errors ~ 90 keV in Sigma and ~ 100
keV in mean value of energy.
19
IV. CONCLUSION
AKNOWLEDGMENT
We present the design and simulation
calculations for the experiment on one- and
two neutron transfer reactions of 24Si(p,d)23Si
and 24Si(p,t)22Si at energy 42 MeV/nucleon.
The experimental configuration is consisted of
a solid-H2 target and five MUST2 telescope
system in order to cover the kinematic range
for detection of deuterons and tritons from the
(p,d) and (p,t) channels. The evaluation for
cross section populating the ground state of
23
Si from (p,d) has been done via DWBA
calculation, whereas for population of the
ground state and the first 2+ state of 22Si from
(p,t) reaction the cross sections have been
calculated via the CRC.
The proposal for the experiment has been
approved by a Program Advisory Committee
(PAC). The experiment is planed to perform
in 2014 at GANIL, France. The experiment
and the data analysis will be driven within a
collaboration between INST Vietnam,
ATOMKI Hungary and MUST2 collaboration.
This research is expected to be part of
French – Vietnamese LIA program. The
Vietnamese authors would like to thank
Vietnam National Foundation for Science and
Technology Development (NAFOSTED) for
the support under the grant number 103.012011.17.
REFERENCES
Particle identification is performed based
on the energy loss correlation in the Si strip
and CsI stages of the MUST2 detector. This
information is really essential to separate the
(p,t), (p,d) and (p,p') channels. The ground
state and the 2+ state of 22Si will be identified
via analysis of energy – scattering angle
kinetic lines.
Simulation for reconstructing the
excitation energy spectrum of 22Si has been
done based on the proposed experimental
configuration, the model-evaluated cross
sections
and
relativistic
kinematic
calculations. The simulation results give a
total statistics of about 300 counts for the
ground state and 120 counts for the 2+ state of
22
Si from (p,t) channel.
[1] O. Sorlin et al., Nucl. Phys. A834, (2010) 400.
[2] Thirolf et al. Phys. Lett. B 485 (2000) 16.
[3] M. Stanoiu et al., Phys. Rev. C 69 (2004)
034312.
[4] E. Becheva et al., Phys. Rev. Lett. 96 (2006)
012501.
[5] O. Sorlin and M.-G. Porquet, Prog. In Part.
And Nucl. Phys. 61 (2008) 602.
[6] N. Keeley, private communication (2011).
[7] J.-C. Thomas, private communication (2011).
[8] S. Ottini-Hustache et al., Nucl. Instr. Meth.
Vol. 431 (1999) 476.
[9] D. Suzuki et al., Phys. Rev. Lett. 103 (2009)
152503.
[10] A. Obertelli et al., Phys. Lett. B 633 (2006) 33.
[11] E. Pollacco et al., Eur. Phys. J. A25 (2005) 287;
[12] http://pro.ganilspiral2.eu/laboratory/detectors/ charged particles/must2/
[13] D.T.Khoa et al, private communication
(2011).
20
Mechanical properties and thermal stability of poly (L-lactic acid)
treated by Co-60 gamma radiation
Tran Minh Quynh1,*, Nguyen Van Binh1, Pham Duy Duong1,
Pham Ngoc Lan2, Hoang Phuong Thao1, Le Thi Mai Linh2
1
Hanoi Irradiation Center, Vietnam Atomic Energy Institute, No.5, Minh Khai, Tu Liem, Hanoi
Hanoi University of Science, Vietnam National University, Nguyen Trai, Thanh Xuan, Hanoi
*
2
Abstract: Poly (L-lactic acid) (PLLA) was mixed with 5 wt% polyethylene glycol 1000 g.mol-1 (PEG)
as a plasticizer and 3 wt% triallyl isocyanurate (TAIC) as a crosslinking agent for preparation of the
plasticized PLLA films. The crosslinking plasticized materials were prepared from the plasticized
PLLA by irradiation with various radiation doses under the Cobalt-60 gamma radiation source at
Hanoi Irradiation Center. The crosslinking structures were introduced in different formulations of
PLLA, and the crosslinking density increased with radiation dose and seemed to be saturated at 50
kGy. The resulting stable crosslinking network inhibited the mobility for crystallization of PLLA
chains. As a result, thermal stability of the crosslinking plasticized PLLA increased, and the
plasticized PLLA crosslinked with TAIC at 50 kGy become much higher than that of initial PLLA
with a very small endothermic peak at its melting temperature in the DSC thermogram. The stressstrain curves of the crosslinking plasticized PLLA showed the toughness of the materials reduced but
still higher than that of initial PLLA, whereas its tensile strength was much improved by radiation
crosslinking.
Keywords: L-lactic acid, polyethylene, crosslinking, thermogram.
I. INTRODUCTION
By the end of the last century,
biodegradable polyesters have been attracted
great attention from scientists and managers as
the promising candidates to replace for
synthetic plastics and polymers, which are
usually none or less degraded for long time
after disposal to the environment. Among
these, poly (L-lactic acid) (PLLA) is a
polyester, which can be produced from
renewable resource has been much studied [1].
Since PLLA is a thermoplastic polymer with
good biocompatibility, non-toxic and having
relative high tensile and performance, it has
been applied in various fields, from medicine,
agriculture, biotechnology, industry to
environment [2]. However, the number of
PLLA application is still limited because its
poor thermal stability as well as its low tensile
strength and modulus, which are not met
requirements of industrial processing. PLLA
can be processed using injection-molding,
compression-molding,
extrusion
and
thermoforming etc. but some drawbacks
including high cost, brittleness, toughness, and
low thermal distortion temperature limitted its
applications. The material properties and
processibility of PLLA have to be improved
for expansion its applications. Many different
methods were applied to improve not only its
thermal stability but also other properties such
as copolymerization, blending with other
monomers or polymers having high thermal
stability, stereocomplexation between L- and
D-enantiomers,
annealing
treatment,
plasticization, and crosslinking [3].
Modification of PLA by copolymerization
or physical blending is useful tool for
decreasing its brittleness, and heat distortion
temperature. Various additives such as
plasticizer, toughening agents, reinforcing
fillers and compatibilizers were incorporated
MECHANICAL PROPERTIES AND THERMAL STABILITY OF POLY (L-LACTIC ACID)…
into PLLA matrix [4]. Recently, radiation
crosslinking was also proved to be a useful
method for enhancing the mechanical and
thermal stability of PLLA [5]. Ionizing
radiation can be applied as an initiation agent
replacing for the chemical initiators in
polymerization
reactions.
Radiation
degradation is applied to prepare shorter
segments with the same characteristics of the
origin materials. Radiation crosslinking and
radiation grafting are also applied to create
new materials with improved properties [6-9].
In recent studies, triallyl isocyanurate (TAIC)
has been proved as the best crosslinking agent
for preparation of the crosslinked PLLA, and
the gel fraction of the radiation-induced
crosslinking PLLA increased with the ratio of
TAIC to 3% and leveled off, suggested that
the 3% TAIC was enough for the radiation
crosslinking PLLA samples with high
crosslinking density [10]. Our previous results
also revealed that the heat resistance of the
radiation crosslinking PLLA materials is much
improved, but the crosslinked materials
become harder and more brittle.
NatureWorks (Malaysia branch). PEG 1000
and TAIC were bought from Sigma Aldrich
(United State) and Tokyo Chemical Inc.
(Japan), respectively.
B. Sample
treatment
preparation
and
Irradiation
PLLA (92%), PEG 1000 (5%) and TAIC
(3%) were melt-mixed at 180  5C in the
plastic mixer (Brabender, Haake, Germany)
into homogenous blend. About 14 g blend
were put between 2 stainless steel molder,
preheated to 180C for 3 min, hot-pressed at
the same temperature under 150 kg/cm2
pressure for other 2 min, then cold-pressed
using water circulation. The resulting PLLA
films were sealed in PE bag, and irradiated in
air at the same dose rate of about 4.3 kGy per
hour with various radiation doses under
Cobalt-60 gamma source at Hanoi Irradiation
Center.
C. Characterization
The radiation crosslinking PLLA samples
were characterized by the crosslinking density
and structure. In this study, the crosslinking
densities obtained in the crosslinking samples
were measured by gel fraction in chloroform
according to following equation:
Recent studies of PLLA plasticized with
polyethylene glycol (PEG) have indicated that
the efficiency of plasticization increased with
decrease of PEG molecular weight [11]. In a
previous study, we found that 5 wt% of PEG
1000 is suitable to improve the toughness of
the radiation crosslinking PLLA [12].
Therefore, in the present study, the
crosslinking PLLA films were prepared from
PLLA/5%PEG1000/3%TAIC by gamma
irradiation, and their thermal stability and
mechanical properties were investigated with
radiation dose.
Gel fraction (%) = (Wg/W0)  100
(1)
where W0 is weight (dry) of the crosslinked
PLLA, Wg is the weight remaining (dry gel
component) of the crosslinked film after
dissolved in chloroform at RT for 24 h.
The structure of the crosslinking gels
formed in irradiated polymers determined
their capacity in adsorption of solvent.
Therefore, the dried PLLA gels were
immerged in chloroform and their swelling
degree (time) was calculated by the following
equation:
II. EXPERIMENTAL
A. Materials
PLLA pellet (4042D grade, melting point
of about 160C) was purchased from
Degree of swelling (time) = (Ws - Wg)/Wg
22
(2)
TRAN MINH QUYNH et al.
where Wg is the weight of the dried gel
extracted from the crosslinking PLLA, Ws is
the weight of the gel swollen in chloroform at
RT for 48 h. P and CHCl3 are densities of
PLLA and chloroform, respectively.
About 5 mg of PLLA was
aluminum pan, sealed and set in
holder of a differential scanning
(DSC). The sample was heated
sample holder, heated from room temperature
to 500C with a heating rate of 10C per min
under nitrogen flow of 30 mL per min, and the
amount and rate of change in the weight of a
material were recorded with temperature.
Dynamic mechanical analyses (DMA) of the
typical crosslinking PLLA samples were
carried out with a DMA-7e (Perkin Elmer,
Malaysia Nuclear Agency). The film was cut
put in the
the sample
calorimeter
from room
into a rectangular specimens of 20  12  0.5
mm. Measurements were performed at a
frequency of 1 Hz under nitrogen atmosphere
from 30 to 200C with heating rate of 5C per
min.
temperature to 200C in air, then cooled with
the same heating and cooling rate of 10C per
min. Melting point (Tm), glass transition
temperature (Tg) and enthalpy of melting
(Hm) of each sample from DSC
thermogram. And its degree of crystallization
was calculated as follow:
PLLA sheets were cut into dumbbell
samples of Type V according to ASTM D
638. The sample was fixed in the gauges form
the top, provided that the length between 2
gauges was kept at a determined distance.
Mechanical properties of PLLA samples were
measured using a tensile with a 10 kN load, 5
mm.min-1 in crosshead rate. Stress-strain
curve was recorded with time at room
temperature and the mechanical properties
were determined by the film thickness. At
least 3 samples were tested for each material.
c (%) = 100  (Hcc + Hm) / (3)
where Hcc and Hm are enthalpies of melting
and crystallization, respectively. Heat of
fusion of PLLA crystal (Hf) is 135 J.g-1 as
determined by Miyata and Masuko [13].
Thermal degradation behavior of PLLA
was investigated by a thermo gravimetric
analysis using a TG/DTA (Institute of
Chemistry). About 10 mg sample was put on
Table I. Gel fraction and swelling degree of the radiation-induced crosslinking PLLA/5%PEG/3%TAIC
with radiation dose
Radiation dose
(kGy)
Gel Fraction
(%)
Degree of Swelling
(time)
Non-irradiated
ND
-
10
ND
-
20
9.04
35.26
30
67.30
26.86
50
85.42
22.70
100
88.64
10.53
ND: Non-detected
23
III. RESULTS AND DISCUSIONS
introduction of the crosslinking network in the
plasticized PLLA samples. Figure 1 shows
one possibility of the crosslinking network
produced in the plasticized PLLA by gamma
irradiation.
A. Gel behavior of the radiation crosslinking
PLLA samples
Gel fractions of the irradiated samples
were determined with radiation dose as
presented in Table I. The results indicated that
the crosslinking networks was not produced in
the PLLA/PEG/TAIC by gamma irradiation
with the dose below 10 kGy, though TAIC has
been proved as a good crosslinking agent for
PLLA [5, 10]. It may be due to the presence of
oxygen during irradiation for the PLLA films
in our present study accelerated oxidation and
prevented the formation of crosslinking sites
at low radiation dose. Also, the presence of
PEG may inhibit the recombination of
macromolecular radicals formed during
gamma irradiation.
Table I also revealed the swelling
behavior of the crosslinked gels. It is
interesting that the swelling degree quickly
increased with increasing of radiation dose to
30 kGy, then significantly decreased with
higher radiation doses, though the gel fraction
almost the same. This was attributed to the
change of the crosslinking structure. In
generally,
radiation
degradation
and
crosslinking coin concurrently occurred in the
plasticized PLLA during irradiation, but the
presence of crosslinker, TAIC speeded up the
crosslinking between the polymer chains as
observed from Figure 1. With increasing of
radiation dose, the number of radicals
increased. As results, the probability of
crosslink between polymer and crosslinker
also increased, and tighter crosslinking
networks with higher crosslinking point were
formed in the samples irradiated at higher
dose, and their degree of swelling decreased.
A significant insoluble gels were
observed in other samples irradiated with dose
higher than 20 kGy. The gel fractions of
PLLA/PEG/TAIC are 9.04, 67.3, 85.43 and
88.64% by irradiation at 20, 30, 50 and 100
kGy, respectively. The gel fraction quickly
increased with radiation dose to 50 kGy and
leveled off with further increasing of radiation
dose up to 100 kGy. These results suggested
that the dose of 50 kGy is enough for































 Irradiation
PLLA chain
PEG1000 chain
TAIC molecules
Fig. 1. Possible crosslinking network formed in the irradiated PLLA/PEG/TAIC
24
Table II. Thermal properties of PLLA/PEG/TAIC with radiation dose
Radiation dose
Tg (C)
Tcc (C)
Tm (C)
Hm (Jg-1)
c* (%)
Neat PLLA
58.01
128.40
152.40
21.11
16.02
Non-irradiated
37.88
112.63
148.70
20.46
15.16
10 kGy
38.24
112.53
147.35
18.54
13.73
20 kGy
39.73
114.89
146.99
14.91
11.04
30 kGy
42.83
-
144.24
0.49
0.36
50 kGy
44.07
-
144.56
0.37
0.28
100 kGy
39.69
-
146.43
5.78
4.28
Fig. 2. Thermo gravimetry thermographs of PLLA (a); plasticized PLLA (b); the plasticized PLLA
irradiated at 10 (c); 20 (d); 30 (e) and 50 kGy (f).
of the plasticized PLLA recovered by gamma
irradiation. The stable crosslinking networks
introduced to PLLA restrained the mobility
for crystallization of polymer chains. As
results, degree of crystallization of the
crosslinked PLLA reduced with radiation
dose. The higher the radiation dose, the lower
is the crystallization degree. Even the
plasticized PLLA crosslinked at dose higher
than 30 kGy showed no crystallization and
very small melting peak. These results
suggested that the crosslinking samples
become more stable when temperature rises.
B. Thermal properties and stability of the
crosslinking PLLA
DSC thermograms of neat PLLA and
crosslinking plasticized PLLA samples were
recorded with temperature, and their thermal
properties were presented in Table II. As one
can see, the glass transition, cold
crystallization and melting temperature of
initial PLLA were much reduced by adding
5% PEG and 3% TAIC. This may due to the
plasticization effect of PEG for PLLA.
However, the glass transition temperature (Tg)
25
This result is entirely suitable with our
previous studies on the thermal properties of
the radiation induced crosslinking PLLA [10].
TGA curves for different PLLA samples
were showed in Figure 2. PLLA started to be
As on can see from Table III, the initial
decomposition temperature for plasticized
PLLA was 276.2C, and about 87.4%
PLLA/PEG/TAIC were thermal degraded at
pyrolysed at around 285C and its weight
around 300C, its remaining mass exhibited a
higher heat resistance and seemed to be
rapidly reduced with temperature to 350C.
While the plasticized PLLA displayed twostep degradation with heating, the crosslinking
PLLA showed single-step decomposition
similar with initial PLLA. Thermal stability of
PLLA much reduced by adding of PEG and
TAIC, but it recovered by gamma irradiation.
It suggested that the crosslinking networks
produced in polymer made it become harder to
be melted and thermal degraded.
completely degraded at around 400C. The
two-step degradation may be due to the
crystallization domains of PLLA or PEG did
not be plasticized, still kept thermal stability
like initial PLLA. All crosslinking PLLA
samples become more stable with heating. The
temperature where 50% sample mass was
pyrolysed for the crosslinking PLLA increased
and its weight loss decreased with radiation
dose.
Table III. Thermo gravimetric data of the crosslinking plasticized PLLA
Samples
Tonset (C)
Tmidset (C)
Weight Loss (%)
Initial PLLA
285.7
309.9
98.4
PLLA/PEG/TAIC
276.2
298.9
99.4
PLLA/PEG/TAIC-10 kGy
273.5
304.7
92.9
293.1
318.2
97.0
311.2
344.6
96.4
325.2
357.7
96.0
Table IV. Mechanical properties of PLLA, plasticized and crosslinking PLLA samples
Samples
Tensile strength
(MPa)
Young’s modulus
(MPa)
Elongation at break
(%)
Initial PLLA
51.76
804.77
3.5
Plasticized PLLA/PEG/TAIC
38.63
523.63
256.8
32.62
579.21
200.1
42.32
679.57
68.2
47.54
737.61
28.6
53.11
841.53
13.7
58.18
777.04
10.3
26
3.5
3.0
Initial PLLA
tan 
2.5
Plasticized PLLA
2.0
Crosslinking PLLA-50
1.5
1.0
0.5
0.0
30
40
50
60
70
Temperature
80
90
100
(o C)
Fig. 3. Tan  of different PLLA samples with temperature
Stress–strain curves of the different PLLA
films were recorded using a tensile tester, and
their mechanical properties were presented in
the Table IV. Initial PLLA shows rather high
modulus and tensile strength meet the
requirements of many applications, but its
toughness is not enough for the application in
industry with low elongation at break of 3.5%
only. After mixing with PEG, the elongation
at break of plasticized PLLA was about 80
times of the value of initial PLLA, whereas
it’s tensile and modulus reduced. The tensile
strength and young’s modulus of the
plasticized PLLA were recovered by gamma
irradiation, while their elongation at break
gradually reduced, but still higher than that of
initial PLLA. These results suggested that the
radiation induced crosslinking PLLA become
harder and tougher, namely is more stable in
mechanical aspect.
transition temperature (Tg) of the polymer
samples. The temperature and intensity of the
tan delta peak of PLLA were obviously
decreased by plasticization effect of PEG,
suggested that the presence of plasticizer
retarded the segmental motion of polymer
matrix during the transition. However, their
mobility might be somewhat recovered by
gamma irradiation. Thus, the crosslinking
network inhibited the motion of PLLA chains
for crystallization, but not for transition.
IV. CONCLUSION
The crosslinking network was introduced
into the PLLA/PEG/TAIC during gamma
irradiation. The gel fraction of the crosslinking
samples increased and their degree of swelling
decreased with radiation dose. PEG of 5 wt%
and radiation dose of 50 kGy are considered to
be optimal condition to prepare the
crosslinking plasticized
material
with
crosslinking density of about 85 %.
Plasticization effect of PEG was much
reduced the thermal properties of PLLA, but
the crosslinking network made the materials
become more stable with heating and the
crosslinked at dose higher than 30 kGy
Dynamic mechanical analyses (DMA) of
typical PLLA samples were investigated for
clarification their miscibility and glass
transition temperature. Figure 3 shows the tan
delta of initial PLLA, plasticized and
crosslinked PLLA as functions of temperature.
The peak of tan  revealed as the glass
27
required the higher temperature for pyrolysis
of 50 % initial mass, even Tmidset of the
PLLA/PEG/TAIC-50 kGy about 50C higher
than that of initial PLLA. The flexibility of
PLLA much increased by plasticization, while
it’s tensile and modulus reduced. The
mechanical stability of the plasticized PLLA
was recovered by radiation crosslinking.
Elongations at break of the crosslinking PLLA
samples were reduced, but still higher than
that of initial PLLA. Thus, mechanical
properties of PLLA were significantly
improved by radiation crosslinking.
[4] Garlotta D. J. Polym Environ 2001, 9(2): 6384.
[5] Jin F, Hyon SH, Iwata H, Tsutsumi S.
Macromol. Rapid Commun 2002, 23:909-12.
[6] Chapiro A. In Radiation Chemistry of
Polymeric System. Jhon Wiley & Sons, New
York. 1961. p.1.
[7] Nikitina TS, Zhuravskaya V, Kuzminsky AS.
In Effects of Ionizing Radiation on High
Polymers. Gordon and Breach Inc, New York.
1963.
[8] Olejniczak J, Rosiak J, Charlesby A. Rad
Phys Chem 1991, 38:113-118.
[9] RJ Woods, AK. Pikaev. Applied Radiation
chemistry: Radiation processing. John Wiley
& Sons. NewYork 1994, pp. 343-357.
[10] Mitomo H, Kaneda A, Quynh TM, Nagasawa
N, Yoshii F. Polymer 2005, 46:4695-03.
[11] Kulinski Z, Piorkowska E, Gadzinowska K,
Stasiak M. Plasticization of poly (L-lactide)
with
poly
(propylene
glycol).
Biomacromolecules 2006, 7(7): 2128-2135.
[12] Quynh TM, Diep TB, Mohammed IS,
Kamaruddin BH. Improvement of thermal
stability of the plasticized poly (L-lactic acid)
PLLA by radiation crosslinking. Nuclear
Science and Technology 2012; 6: 1.
REFERENCES
[1] Stevens ES In Green plastics: an introduction
to the new science of biodegradable plastics.
Princeton University Press. 2002.
[2] Drumright RE, Gruber PR, Henton DE. Adv
Mater 2000, 12(23):1841-1846.
[3] Quynh TM, Mitomo H, Nagasawa N, Wada
Y, Yoshii F, Tamada M. Properties of
crosslinked polylactides (PLLA & PDLA) by
radiation and its biodegradability. Eur Polym
J, 2007, 43(5): 1779-1785.
28
Studying agents causing respiratory disease in the airborn
at Institute for Nuclear Science and Technology’s area, in Hanoi
Nguyen Thuy Binh1, Vo Thi Anh1, Nguyen Thu Ha1, Ha Lan Anh1,
Nguyen Hong Thinh1, Do Thi To Uyen2, Pham Quang Thang3
1
Institute for Nuclear Science and Technology,
2
Institute of Biotechnology,
3
Institute of Environmental Technology, Vietnam Academy of Science and Technology.
(Received 02 May 2013, accepted 17 September 2013)
Abstract: The aerosol sampler-Gent Stacked Filter Unit (GENT-SFU) located on the top roof of the
third floors building of Institute for Nuclear Science and Technology. The amount of aerosol particle
and their components such as black carbone, chemical elements, ions, volatile organic compounds and
microorganisms are identified by the appropriate analysis methods. The regression method and
analysis of variance were used to find out the correlation between pollution effects and number of
patients treated at the respiratory clinic of E hospital, Hanoi. The results showed that microorganisms,
benzene, toluene, element sulfur, element silic have influence over the number patients treated for
respiratory-related disease treatment on a monthly at the E-hospital- Hanoi.
Keywords: Aerosol particle, chemical element, volatile organic compound, microorganisms, E-hospital.
The World Meteological Organization
(WMO) has warned us about potential risk
causing fatal that signs of increasing in the
countries with strong economic development,
especially in the major cities in Asia and
South America. The WMO also warned the
phenomenon of increasing temperature of the
earth to increase atmospheric pollution, global
desertification and sandstorms. The increase in
the frequency and extent of forest fires also
cause air pollution.
such as Hanoi, Hochiminh city, Danang...lead
to activities in industry production,
construction and transportation, it have
increased the level airborn in the air pollution.
The major sources of urban pollution in cities
include transport, industry and construction.
Studies have pointed out the economic
damage in cities and rural areas due to air
pollution. Data from the labor Health institute
reported that Hanoi losses about 1 billion
VND per day because of air pollution from
exhaust gas from motorbikes. Another study
in 2007 was carried out by Vietnam
Environment Protection Agency in Phutho and
Namdinh province, it showed that economic
loss caused by health impact of air pollution
has been estimated about 295 000
VND/person/year,
corresponding
to
approximately 5,5% GDP.
In Vietnam, Economic development,
mechanical population growth in major cities
The previous studies of air pollution are
only of monitorning the level amount of
I. INTRODUTION
The social and economic development in
each country, especially in developing
countries, environmental problems become
more serious, in which air pollution impact
directly on climate change and impact on
human health.
STUDYING AGENTS CAUSING RESPIRATORY DISEASE IN THE AIRBORN AT…
aerosol particles in air, some inorganic
fluorescence spectrometer X-VietSpace was
used with working regulation: sample size
mode HV=30kV, I=200 µA, no filter;
spectrum record time 1200 sec.; working
environment- primary vacuum; data analysisautomatic.
components and make some assessmanent of
their source. The studies about correlation
between environmental factors affecting
human health are limited.
In frame of this study, we have built the
method to collect and analyses some polluted
effects in airborn (such as volatile organic
compounds-BTEX, microorganisms), Study
the correlation between polluted effects and
their impacts on respiratory diseases.
The ions of particles PM are detetminated
by Dionex-600 Ion Chromatography with
Peaknet 6.0 software.
The volatile organic compounds-BTEX
such as benzene, toluene, ethylbenzene, mxylene, and p-xylene were collected by active
method. FL-1001 pump to absorb air into
adsorption tube with flow rate 50ml/minute
collecting time on each adsorption tube is 25
minutes. We collect two tubes for each
sampling with the collecting time separated 10
minutes. The adsorption tubes, which are
maintained in safety box for VOCs analysis,
are covered tightly by specialized Teflon cap.
The samples are desorbed and analyzed in
GC/MS-QP 2010 (Gas chromatography-Mass
spectrometry).
II. METHODS
The aerosol sampler- Gent Stacked Filter
Unit (GENT-SFU) is used and located on the
top roof of a three-floor builbing of Institute
for Nuclear Science and Technology (INST)
with longitude 105o47.56’, latitude 21o2.46’.
Due to the equipment used in conjunction with
other research, so the average sampling time
of 24h did not perform. Based on the ability of
sampling and topography where the aerosol
sampling is located, the samplers were taken
from 16 pm to 8 am. Nuclepore polycarbonate
filter with diameter 47 mm was used to collect
dust particles PM2,5 and PM2,5-10.
The impingement method is suitable
technical condition for collecting bioaerosol.
The airflow impinged into liquid medium. The
airflow impinged into 250 ml glass flask
containing 100 ml liquid nutrient medium.
The glass flask is connected with the pump by
teflon tube Ø= 5 mm. After that, solution
sample is enriched and analysis the
microorganism. Total microorganisms are
finding out by counting colonies forming unit
(CFU) on medium agar disk. Cell morphology
and Gram bacteria are finding out by Gram
stain method and PCR method (polymerase
chain reaction). The maintain goal of methods
is detection microorganism species which are
isolated.
The amount of particles PM on the filters
is determined by weight method. The
difference in weight of filter after and before
collecting is an amount PM particles and
concentration of PM particles is a quotient of
amount dust on the filter and air volume
passing through the filter.
The Black Carbon substance is
determined by light intensity measurment
method.
The chemical elements are determined by
XRF (X-ray fluorescence). The X-ray
30
NGUYEN THUY BINH et al.
Fig. 1. PM2.5 and PM2.5-10 particle concentrations collecting in Institute
for Nuclear Science and Technology
Fig. 2. The concentration of black carbon of PM particles
The variance analysis ANOVA was
carried out with the obtained numbers in order
to study the correlation between there
pollution components and the effects on
human’s health.
for 70% of the total of PM. The black carbon
of PM2,5 is accounted for nearly 67% of total
amount of black carbon sample. The results
presented in fig. 2.
The results is shown that the chemical
elements such as Al, Si, S, K, Ca, Ti, Mn, Fe,
Cu, Zn and Zr are detected in all samples, but
concentration of elements on coarse
particulars is difficult on fine filter. If
concentration of chemical elements arranged
in line from high to low is S > S i> Ca >K >
Al of PM2.5 that concentration of chemical
elements of PM2.5-10 will be Si > Al > S > Ca >
K (see Fig. 3 and Fig. 4).
III. RESULTS AND DISCUSSION
The amount PM particle of aerodynamic
size 2.5m PM2.5 called fine particle and
particulates of aerodynamic size 2.5-10m
PM2.5-10 called coarse particle collecting in
INST are described in fig. 1 from April 2011
to Mar 2012. The amount of PM2,5 is always
higher than PM2,5-10. The highest amount of
PM2,5 is up to 236µm/m3 and PM2,5 accouted
31
Fig. 3. The concentration of elements of PM2.5 particles
Fig. 4. The concentration of elements of PM2.5-10 particle
Anion such as F-; Cl-; Br-; NO3-; PO43-;
SO42- and cation such as Na+; NH4+; K+; Mg2+;
Ca2+ are detected in all samples. The results of
ion chromatography analyze shown that
concentration of anion are arranged in line
from height to low SO42- > Cl- > NO3- > F- >
NO2- > PO43- of PM2.5 and SO42- > Cl- > NO3> PO43- >
NO2- > F- of PM2.5-10
concentration of cation are arranged in line
from height to low : NH4+ > Ca2+ > K+ > Na+
> Mg2+ of PM2.5 and Ca2+ > NH4+ > Na+ >
Mg2+ > K+ PM2.5-10. All major ions in PM2.5
films were detected.
Benzene, toluene, o.m.p-xylene (orto-.
Meta and para-xylene) are volated organic
compounds BTEX group are detected in all
collected samples. The highest concentration
of BTEX found in 12/2011 is 7.615µg/m3 and
the lowest concentration in 5/2011is 28.83
µg/m3 (Table I).
32
Table I. VOC data, rainfall data, humidity data and temperature data
Month/
year
Temp
(OC)
Humidity
(%)
Rainfall
(mm)
Benzene
(µg/m3)
Toluene
(µg/m3)
EthylBenzen
(µg/m3)
m.pXylene
(µg/m3)
o-Xylene
(µg/m3)
5/2011
25.25
84.75
149
8.44
32.82
10.09
9.66
6.89
6/2011
27.75
89.00
396
15.71
37.74
13.56
16.75
9.88
7/2011
28.40
84.20
295
15.51
12.19
5.02
4.30
1.13
8/2011
28.00
84.00
313
18.72
28.63
5.05
11.00
4.02
9/2011
26.67
87.00
247
21.67
42.06
14.78
23.09
12.43
10/2011
24.00
91.75
178
23.77
49.84
33.53
68.03
28.63
11/2011
20.50
88.50
32
25.43
43.19
33.53
60.09
23.54
12/2011
17.20
65.00
52
27.62
77.51
26.75
44.83
16.67
1/2012
14.00
82.00
20
28.83
78.22
10.62
23.67
9.47
2/2012
15.50
86.25
19
23.23
44.69
7.00
17.82
5.53
3/2012
18.80
95.40
17
19.89
43.34
8.39
13.27
8.12
4/2012
24.75
88.25
123
17.71
38.79
4.95
10.08
3.91
Table II. The number of microorganisms in different months
Month/year
Microorganisms
Humidity
(%)
Temperature
(C)
Rainfall
(mm)
3/2011
88568
78%
16
18
4/2011
12867
79%
24
41
5/2011
2570
80%
26
149
6/2011
3191
91%
28
396
7/2011
15091
79%
30
295
8/2011
6819
83%
29
313
9/2011
6348
87%
26
247
10/2011
1070
84%
25
178
11/2011
8433
88%
21
32
12/2011
1316
74%
15
52
1/2012
2465
78%
14
20
2/2012
3/2012
17857
11484
87%
92%
15
19
19
17
The results show that the highest number
of microorganism on day is 37*104 ± 1.7* 104
CFU/m3. The highest average result is 88.57
CFU/m3 in March 2011 and the lowest
highest average result is 10.70 CFU/m3 in
October
2011.
Genus
Pseudomonas,
Staphylococcus and Aspergillus’s were
determined in collected samples. Negative
gram bacteria samples ranged from 2% to
15%.
33
the benzene, toluene, ethylbenzene content
and the average rainfall through months is
presented in the following equation with the
Significance F=0.0099<0,05:
The correlation between sulfur S and
sulfate SO42 content in PM2.5 fine dust is
shown in the following equation with
significance F=0,001<0.05
S  20.36  2.38  [ SO42 ]
(1)
Microorganisms = 15874.72+[Benzen]* 27.18
– [Toluen]* 376.78 – [Ethylbenzene]* 235.37
–[Rainfail]* 24.12
(4)
It shows that the appearance of S in fine
dust causes of the conversion from SO2 to
sulfate through a chemical process under the
impact of UV and humidity. Only a part of
sulfate is the result of the transformation from
SO2 in the local scope, the other part is due to
the process of distributed. In Hanoi, there are
numbers of factories and small factories that
still use poor quality coal, in addition to the
habit of using cheap fuel sources in the daily
life of the people is the cause that leads to the
high concentration sulfate SO42-.
This can be explained as the cause of the
spreading of organic compounds as well as
microorganisms on fine dust particles and in
the air, dust and gas emissions in the air under
the impact of rainfall, toluene and
ethylbenzene. So the correltion co-efficients
between microbial populations and rainfall
toluene and ethylbenzen have negative value
(-24.12; -376.78; - 235.37).
The Institute of Nuclear Science and
Technology is located in Cau Giay district,
and nearly E hospital. The patients with
insurance in Cau Giay district are registered
for medical examination and treatment at the
E Hospital. We have collected the number of
patients hospitalized at the Department of
Respiratory to find out the impact of
pollutants on the number of people living
around the examined area.
The interaction between the number of
black carbon and organic compounds BTEX
group for both types of dust PM2, 5 and
PM2,5-10 is shown in the following equation
with significance F=0.01<0.05:
BC(PM2,5)= 5.00-0.2*[Benzen]
+0.04*[Toluen]+0.05*[Ethyl Benzen]
(2)
and with Significance F=0.009<0.05:
BC(PM2,5-10)=2.55-0.09*[Benzen]
+0.02*[Toluen]+0.01*[Ethyl Benzen]
The regression function was used to find
the relationship between the number of
patients and the number of bacteria per month,
we have a function:
(3)
Black carbon in dust and gas is formed
through the incomplete combustion of fuel
and the effect of organic carbon absorption
and scraps of minerals. It can affect the
transport and fate of organic matter pollution
through the carbon black-organic minerals
compound.
Patients = 112.91+0,003*[Microorganisms]
- 0,012*[Rainfall]
(5)
In which Significance F= 8.92E-06-07<0.05.
It’s clear that the bacteria in ambient air
collected at the Institute of Science and
Technology areas of nuclear has the
correlation to the number of patients live in
Cau Giay who are under the treatment in the E
Hospital, Hanoi.
Microbial populations in the natural
environment withstand the impact of the
components of pollution in the air. The
correlation of microbial populations in the air,
34
Table III. The number of microorganisms, humidity, temperature, rainfall and the number of
patients in the Department of Respiratory
Month/
year
Microorganisms
(CFU)
Humidity
(%)
Temperature
(oC)
Rainfall
(mm)
Patients
3/2011
88568
78%
16
18
343
4/2011
12867
79%
24
41
197
5/2011
2570
80%
26
149
101
6/2011
3191
91%
28
396
122
7/2011
15091
79%
30
295
175
8/2011
6819
83%
29
313
126
9/2011
6348
87%
26
247
117
10/2011
1070
84%
25
178
88
11/2011
8433
88%
21
32
143
12/2011
1316
74%
15
52
97
1/2012
2465
78%
14
20
99
2/2012
17857
87%
15
19
169
3/2012
11484
92%
19
17
158
The relationship between the patients, the
total anion content of SO42-, the number of
microorganisms was shown in the equation
below:
Patients = -88.5+0.31*[SO42- ]
+0.006*[Microorganisms]
The polluted components in air entered in
the body and accumulate over time. The
pollution level is not too high and still in the
threshold. However, everyday people have to
breathe the air that is containing a certain
amount of pollutants, they will penetrate the
respiratory tract, accumulate in the body and
cause disease. Therefore, the levels of
pollutants are potentially harmful to humans,
as they exist in the environment and humans
breathe them in a while.
(6)
in which Significance F= 0.00017<0.05.
The relationship between the patients, the
Microorganisms, Silic (Si) amount and Sulfur
(S) amount in PM2,5 dust is shown in the
equation below:
The Table IV is the data which was
collected at National Lung Hospital. It shows
that the number of people treated at the
Department of obstructive lung disease
increased by more than 50% after two years
(in 2009 the number of patients was 509, in
2011 increased to1014 people). The number of
patient at the Department of pleural disease
after two years increased from 543 in 2009 to
849 in 2011. According to the latest statistics
of the hospital, after 2 years, the number of
patients with lung disease increased by 52%.
Patients =69.49+0.006*[Microorganisms]
+2.123*[ Si_Fi]+0.012*[S_Fi]
(7)
In which Significance F= 0.0006 < 0.05.
From there, we can get the levels of
bacteria, benzene, toluene, ethylbenzen, the
total amount of SO42- anion, the total amount
of silic and sulfur in the examined area have
an impact on the number of patients at the
department of Pneumology, E Hospital Hanoi.
35
Table IV: The number of patients in Examination Department at National Lung Hospital
Year
2009
2010
2011
Number of patient visits
35255
38520
40287
Male
21116
23468
24485
Female
14119
15052
15802
Number of patients
32093
33847
35786
Number of children
1620
1658
1720
Patients with insurance
5941
9651
12681
Pulmonarytuberculosis
7140
7578
7501
Extrapulmonary tuberculosis
3563
3636
3341
Lung disease
16356
16963
19826
Emergency department
522
456
360
TB department
1507
1146
1313
272
184
CPR department
Pulmonary infection deprtment
1534
1299
1488
Department of Obstructive pulmonary
dissease
509
1038
1014
Department of pleural disease
543
729
849
Department of cancer
1666
2071
2616
Pediatric department
308
344
326
Surgery
114
Total number of patients in hospital
8401
9375
10233
Pulmonary tuberculosis
1765
1635
1326
Extrapulmonary tuberculosis
1983
1965
1820
Lung disease
4653
5775
7083
Source: The Scientific Research Department – National Lung Hospital
In Pediatric clinic at Bach Mai Hospital,
the number of patients with respiratory
diseases increased in winter (months 1, 2, 3)
by 57.4% (Table V)
industrial, handicraft workshops, and the
mechanical population growth in the city led
to urbanization planning which lead to an
increase in number of vehicles. The
environment is now under a large amount of
emissions and human have to bear the
consequences. They will have to contact,
breath and live with considerable amount of
pollutants which will be accumulated in the
body and cause disease.
The data shows that the ambient
environmental quality deteriorate day by day,
natural environment is under the influence of
the negative impact due to the rapid growth of
the economy. It leads to the fast increasing of
36
Table V: The number of patients in Pediatric department – Bach Mai Hospital
Month/ year
Number of
patients
Number of patients
with respiratory
diseases
% Respiratory
diseases
2/2011
1048
302
28.8
3/2011
1492
569
38.1
4/2011
1676
620
37
5/2011
1892
401
21.2
6/2011
1442
365
23.3
7/2011
1336
245
18.3
8/2011
1511
502
32.2
9/2011
1623
539
33.2
10/2011
1559
506
31.2
11/2011
1357
122
12/2011
1376
499
36.3
1/2012
1685
597
35.4
2/2012
1124
329
29.3
3/2012
1040
429
41.3
relationship of pollution agents to patients
with respiratory diseases.
IV. CONCLUSIONS
This result is just the initial study,
because the examined location is at a point
that located relatively high above the ground.
It also shows the influence of the components
of air pollution on human health and pollution
levels remain within the threshold. However,
every day people breathe the air containing a
quantity certain pollutants, that pollutants will
penetrate the respiratory tract, accumulate in
the body and cause disease. Therefore, the
levels of pollutants are potentially harmful to
humans, because they exist in the environment
and humans will contact them through
breathing. More studies need carrying out in
the locations that are at lower elevations and
various points in the city. They needed
repeating after 2 to 3 years for us to be able to
assess the broader and learn the changes in the
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38
The isomeric ratios in 107Ag(γ, n)106m,gAg photonuclear reaction
induced in the giant dipole resonance region
Tran Duc Thiep1, Truong Thi An1, Phan Viet Cuong1,*,
Nguyen The Vinh1, Bui Minh Hue1, A. G. Belov2 and O. D. Maslov2
1
2
Institute of Physics, VAST, 10 Dao Tan St., Ba Dinh Region, Hanoi, Vietnam
Flerov Laboratory of Nuclear Reactions, JINR, 141980 Dubna, Moscow Region, Russia
*
(Received 1th August 2013, accepted 29 September 2013)
Abstract: We measured for the first time the isomeric ratios in 107Ag(γ, n)106m,gAg photonuclear
reaction by using the activation method and γ-ray spectroscopic method for the whole giant dipole
resonance (GDR) region. The high-purity natural Ag foils in disc shape were irradiated with
bremsstrahlungs generated from an electron accelerator Microtron. The induced gamma spectra in the
irradiated foils were measured by the high resolution γ-ray spectroscopic system which consists of a
high-purity Germanium detector and a multichannel analyzer. In order to improve the accuracy of the
experimental results the necessary corrections were made in the γ-ray activity measurements and data
analysis. The results were analyzed, discussed and compared with those of other authors. For the
mentioned reaction, the isomeric ratios in the energy range from 14 to 24 MeV bremsstrahlungs in this
work (except the values at 14, 18 and 20) are new measurements .
Keywords: Photonuclear Reaction – Isomeric Ratio – GDR region – Reaction Yield – Impulse.
I. INTRODUCTION
The study of nuclear reactions at
bremsstrahlung photon beam in the giant
dipole resonance (GDR) region has definite
advantages and presents a considerable
interest due to the significant difference from
nuclear reaction induced by other projectiles.
In photonuclear reactions such states are
excited which are usually difficult to be
produced in other reaction types. Although the
cross section of photonuclear reaction is very
low, however the bremsstrahlungs are an
intense source of photon produced by
powerful electron accelerators and the cross
section of photonuclear reaction presents a
wide maximum and as a result, the reaction
yield is significant. Up to now most
investigations were concentrated to nuclear
reactions with proton and neutron while the
data for photonuclear reactions are
incomplete. Therefore, recently the study of
isomeric ratios in photonuclear reactions still
continues to attract interest of many
researchers /1-6 / including natural silver.
Natural silver consists of two isotopes 107Ag
and 109Ag with abundances of 51.35 and
48.65% respectively. There are very few
works devoted to the investigation on
photonuclear reaction of natural silver [11-18].
For isomeric pair 106m,gAg the authors in [ 11]
have measured for 20 and 30 MeV, in [12] for
14 MeV, in [13,14,15] for 30 MeV, in [16] for
18 MeV, in [17] for 50 MeV and the authors
in [11] have theoretically calculated for 20, 30
and 40 MeV with the aid of photon strength
functions proposed by the authors in [18].
There are no data measured for whole GDR
region as well as above this region for
isomeric pair 106m,gAg in existed literature.
The aim of this work is to completely measure
and analyze the isomeric ratio in 107Ag(γ,
n)106m,gAg photonuclear reaction of natural
silver for the whole GDR region. The rationale
THE ISOMERIC RATIOS IN 107Ag(γ, n)106m,gAg PHOTONUCLEAR REACTION…
of the study was the incompleteness and big
discrepancy of the data in this region. It is
expected to obtain new information on the
probability of level population and other
properties of the residual nuclei based on the
measured isomeric ratios.
II. EXPERIMENTAL
Target preparation
The samples for investigation were
prepared from natural silver metal with purity
of 99.99% in disk shape with 1 cm diameter
and their masses were from 0.2545 to 0.3272
g.. Table I shows the decay characteristics of
isomeric pair 106m,gAg which have been
observed in photonuclear reactions of natural
silver with bremsstrahlungs in the GDR
region. The data were taken from [8, 9].
Target irradiation
The sample irradiation in the GDR region
was performed at the electron accelerator
Microtron MT-25 of the Flerov Laboratory of
Nuclear Reaction, Joint Institute for Nuclear
Research Dubna, Russia. The description of
this accelerator and its characteristics are
presented in [10]. The essential advantage of
this Microtron is the small energy spread of
the accelerated electrons (30- 40 keV) at high
beam intensity (up to an average power of 600
W). This allows us to perform the
measurement at strictly definite end-point
energy bremsstrahlung. As an electron-photon
converter was used W disk 4 mm in thickness,
cooled by water. To absorb low energy
electrons passing through the converter in the
irradiation target, an Aluminum screen 20 mm
in thickness was placed behind the converter.
The bremsstrahlung end- point energy of this
accelerator can be varied stepwise from 10 to
25 MeV i.e. the GDR region. The average
electron beam was 12 to 14 µA and the
irradiation time was 60 min.
Table I. The decay characteristics and gamma rays of investigated nucleus 106Ag
Nuclear Reaction
107
Ag(γ, n)106mAg
109
3n)
Reaction
Product
106m
Ag
Spin
Abun.
[%]
Half life
6+
51.35
8.28 d.
Ag(γ,
48.65
Reaction
Threshold
[MeV]
Gamma ray
Energy [KeV]
and
Intensity [%]
Isom.
Trans.
coeff.
IT
9.53
221.7(6.61)
0.0
26.33
406.1(13.5)
106m
Ag
429.3(13.23)
450.9(28.2)
748.4(20.6) *
824.8(15.3)
1045.8(29.6)
1527.6(16.3)
106g
Ag
107
109
*
Ag(γ, n)
106g
Ag(γ, 3n)
1+
Ag
106g
Ag
Gamma rays used for the isomeric calculations
40
24.0
9.07
min
25.99
621.9(0.32)*
TRAN DUC THIEP et al.
bremsstrahlung photon flux; N- the number
of reaction product nuclei;  - the decay
constant and P- the isomeric transition
coefficient, S,  and I - the areas, the
efficiencies and the intensities of the interested
gamma rays; Λi (i = 1÷ 9) are expressions
connected to the irradiating, cooling and
measurement times, E m – the bremsstrahlung
Gamma spectra measurement
The gamma spectra of the samples
irradiated were measured for different cooling
and measurement times with a spectroscopic
system consisting of 8192 channel analyzer
and high-energy resolution (180 keV at
gamma ray 1332 keV of 60Co) HP(Ge)
semiconductor
detector
Canberra. The
GENIE2000 (Canberra) computer program
was used for data processing. The efficiencies
of the detectors were determined with a set of
standard single gamma ray sources calibrated
to 1 - 2 %.
end-point energy,  m E  and  g E  - the cross
sections of the isomeric and ground states
respectively;
(1)
(2)
In the case of bremsstrahlung, the
isomeric ratio is defined as the ratio of the
production yield of the isomeric state to that
of the ground state as follows:
Em
No   m E  E dE
Ethm
- the threshold
Fig. 1 shows a typical gamma spectrum of
natural silver irradiated by 24.0 MeV
bremsstrahlung and measured with the HP
(Ge) semiconductor detector at a distance of 5
cm with the times of irradiation, cooling and
measurement of 60, 30 and 30 min.,
respectively. On this spectrum are marked the
gamma rays characterizing the isomeric and
ground states of isomeric pair 106m,gAg. Other
gamma rays were arisen from different
products of the interaction between natural
silver and the bremsstrahlung. As shown in
Table II there are many gamma rays
characterized for the isomeric state while for
the ground state only one gamma ray of 621.9
keV which were observed in the spectrum. In
principle all gamma rays in Table II can be
used for calculation of the isomeric ratios.
However in practice as it is seen from Fig.1
and Table I gamma rays 221.7, 406.1, 429.3,
450.9 keV characterizing the isomeric state
106m,g
Ag appear against very high Compton
background with gamma rays of 616.2
(21.6), 717.3 (28.9) keV characterizing both
the isomeric and ground states 106m,gAg and
748.4,
824.8, 1045.8 and 1527.6 keV
characterizing the isomeric state 106m,Ag.
Therefore in this case for calculation of the
isomeric ratio gamma rays 748.4 and 1045.8
On the basis of resolving system of
equations (1) in dependence on irradiating,
cooling and measurement times we could
determine the isomeric ratio IR by the
expression below:
IR 
g
E th
Data analysis
Usually the isomeric ratio in a nuclear
reaction is determined by the measurements of
the areas under gamma rays characterizing the
isomeric and the ground states. The equations
that describe the decay of these states can be
written as follows:
Sg  m I m
 3  6  9  1 5  8   3  5  8   3  6  7
1 Sm g I g

IR
 258
and
energies for the isomeric and ground states
respectively.
Isomeric ratio determination
dN m
 N0 m  m N m ,
dt
dN g
 N0 g   g N g  P m N m ,
dt
m
E th
(3)
Em
No   g E  E dE
Ethg
Where m and g- the isomeric and ground
states, N 0 - the target nuclei number,  E  41
keV characterizing the isomeric state and
gamma ray 621.9 keV characterizing the
ground-state can be chosen due to their
highest intensities and lowest intensity errors
[14, 15]. On other hand although the intensity
of gamma ray 1045.8 keV is higher than that
of gamma ray 748.4 keV but the detector
efficiency of gamma ray 748.4 keV is higher
than that of gamma ray 1045.8 keV. In the end
gamma rays 748.4 keV and 621.9 keV were
chosen for calculation of the isomeric ratios of
pair 106m,gAg. This choice made experimental
error lower.
average value IR of those data calculated
from various combinations of a series of
gamma spectra measured for different times of
cooling and measurement. In the experiment
the counting loss was arisen from summing
effect and gamma ray self-absorption. The
summing effect can be reduced or eliminated
by taking a proper distance between sample
and detector, while for reducing the selfabsorption an optimum sample mass is
calculated. These corrections were performed
in the experiment by the methods used in [3,
4]. The main error sources of the isomeric
ratio of pair 106m,gAg were discussed and the
total relative error was estimated of 6.5%.
In our experiment the isomeric ratio was
determined by using expression (2) as the
Fig. 1. A part of gamma spectrum of natural silver irradiated by 24.0 MeV bremsstrahlung measured at a
distance of 5 cm with the times of irradiation, cooling and measurement of 60, 30 and 30 min. respectively.
42
Isomeric ratio
107
Ag(,n)
107
106m,g
Ag
This work
Ref. [11]
Ref. [11] - Calculated
Ref. [12]
Ref. [13,14]
Ref. [15]
Ref. [16]
Ref. [17]
1
Ag(n,2n)
106m,g
Ag
Ref. [19, 20]
Ref. [19,21]
Ref. [19,22]
Ref. [23]
0.1
0.01
15
20
25
30
35
40
45
50
55
Energy (MeV)
Fig. 2. The isomeric ratios of 107Ag(γ, n)106m,gAg and 107Ag(γ, n)106m,gAg reactions.
than that of the ground state when the
bremsstrahlung end-point energy increases. In
107
Ag(γ,n)106m,gAg photonuclear reaction the
GDR region is from the threshold (i.e. about
9.0 MeV) to about 21 - 22 MeV [24]. It means
that for energy region higher than 22 MeV the
isomeric ratio in the mentioned reaction
slightly changes (or almost unchanged).
III. RESULTS AND DISCUSSION
Table II shows the results on the isomeric
ratios obtained in this work and references. It
should be noted that the isomeric ratio is
defined as the ratio of the yield of the highspin state Y(hs) to that of the low-spin state
Y(ls) i.e. IR = Y(hs)/Y(ls). Fig. 2 depicts the
dependences of the isomeric ratio of 107Ag(γ,
n)106m,gAg reaction on bremsstrahlung endpoint energies and 107(n, 2n)106m,gAg reaction
at 14.1, 14.5 and 14.9 MeV neutron energies.
It is well-known that 107Ag is odd-even
nucleus with spin I = 1-/2 determined by the
last odd proton 1g9/2 of fourth shell
1f7/2,2p3/2,1f5/2,2p1/2,1g9/2 [36]. As result
of 107Ag(γ, n)106m,gAg photonuclear reaction,
odd-odd nucleus 106Ag was formed and its
spin is determined by the mentioned odd
proton 1g9/2 and odd neutron 2d5/2 of fifth
shell 1g7/2,2d5/2,2d3/2,3s1/2,1h11/2 [25] and
isomeric pair 106m,gAg was formed at isomeric
and ground state with spins 6+ and 1+,
respectively. One can see from Table II and
Fig. 2 the following facts.
One can see from formula (3) that for the
case of photonuclear reaction with
bremsstrahlung in the GDR region, the
isomeric ratio increases or (decreases) with the
increase of end-point energy, reaches
maximum (or minimum) value at the end of
this region and slightly changes (or almost
unchanged) for higher energies. The change of
the isomeric is due to a fact that the yield of
the isomeric state increases faster or slower
43
a/ There are very few data which are
One can see that in the error limit our results
are in good agreement with the experimental
and insignificantly lower than the theoretically
calculated data from [11], but much lower
than the data from [12, 16]. As mentioned
above in 107Ag(γ, n)106m,gAg photonuclear
reaction the GDR region is from the threshold
(i.e. about 9.0 MeV) to about 21 - 22 MeV.
This means that from 22 MeV above the GDR
region, the isomeric ratio has to be unchanged
or slightly changes. However as it is seen in
Table II at bremsstrahlung end-point energy of
30 MeV the isomeric ratios measured by
authors in [11, 13-15, 17] are in big
discrepancy and the data in [11] are
significantly lower than the data in [13 – 15,
17].
available in the literature to refer the isomeric
ratios in photonuclear reactions with natural
silver in the GDR region as well as in the
higher energy range. We found only seven
experimentally measured data [11-17] and one
theoretically calculated data [11] with the aid
of photon strength functions [18]. There are
only three values of the isomeric ratio for pair
106m,g
Ag are found at 14, 18 and 20 MeV
bremsstrahlung end-point energies. Here the
data in [12] is too high in comparison to that
in [11, 16] as well as to our results. Although
there is a big discrepancy existing among the
data in the literature, however in a general
tendency the isomeric ratio decreases with the
increase of bremsstrahlung end-point energy.
Table II. The isomeric ratios in dependence on bremsstrahlung end-point energies
Nuclear Reaction
Present work
End-point
Energy [MeV]
107
*
Ag(γ, n)106m,gAg
Other works
Isomeric Ratio
R = Y(hs)/Y(ls)
End-point
Energy [MeV]
Isomeric Ratio
R = Y(hs)/Y(ls)
14.0
0.026 ± 0.0017
14.0
2.5 [12]
15.0
0.021 ± 0.0014
18.0
0.06 ± 0.01 [16]
16.0
0.016 ± 0.0011
17.0
0.015 ± 0.0010
20.0
0.015 ± 0.0045 [11]
18.0
0.014 ± 0.0009
19.0
0.013 ± 0.0009
20.0
0.012 ± 0.0008
0.042 [13, 14]
21.0
0.011 ± 0.0007
0.040 ± 0.02 [15]
22.0
0.010 ± 0.0006
0.0160* [11]
23.0
0.011 ± 0.0007
40.0
0.0197* [11]
24.0
0.010 ± 0.0006
50.0
0.023 [17]
Data calculated with the aid of photon strength functions [18]
44
0.0147* [11]
30.0
0.010 ± 0.002 [11]
b/ Our results show that the isomeric ratio
107
by the authors in [26]. The higher the impulse
of the projectile is, the higher the isomeric
ratio is. It is well known that (n, 2n) and (γ, n)
nuclear reactions form the same isomeric pair.
However for the same energies of neutron and
photon, the impulse of neutron in (n, 2n)
reaction is higher than that of photon in (γ, n)
reaction because the photon has zero rest
mass. Therefore the isomeric ratio in (n, 2n)
reaction is significantly higher than that in (γ,
n) reaction. This fact can be seen in [19 – 23]
and presented in Fig. 2. One can see our
results for bremsstrahlung end-point energies
14.0 and 15.0 MeV are significantly lower
than the data for 107Ag(n, 2n)106m,gAg reaction
induced by 14.1 and 14.9 MeV neutrons. This
once again confirms that our results are
logical.
106m,g
in Ag(γ, n)
Ag photonuclear reaction in
GDR region decreases with the increase of
end-point energy, reaches minimum value at
the end of this region (21 - 22 MeV) and
slightly changes for higher energies (23, 24
MeV). This fact was expected from formula
(3) as mentioned above. The results also show
that for isomeric pair 106m,gAg, the yield of
higher spin state increases lower than that of
the lower spin state when the bremsstrahlung
end-point energy increases. In fact at the end
of the GDR region the value of the isomeric
ratio measured in this work is 0.010 ± 0.0006.
Therefore it is expected that above the GDR
region the isomeric ratio has to be about 0.010
± 0.0006. In practice this value is lower than
the data for 30 MeV from [13 -15] and for 50
MeV from [17]. It can be explained as
follows: the isomeric ratio of isomeric pair
106m,g
Ag in natural silver for energy region
higher the GDR region comes from two
107
Ag(γ, n)106gAg and 109Ag(γ, 3n)106gAg
photonuclear reactions. The isomeric ratios of
these two reactions are different due to the
channel effect [26]. The author in [28] show
that the isomeric ratio for one and the same
isomeric pair depends on the mass difference
of the target and product nuclei and the higher
the difference the higher the isomeric ratio.
This means that the isomeric ratio in 109Ag(γ,
3n)106m,gAg is higher than that in 107Ag(γ,
n)106m,gAg. As a result, the isomeric ratio for
isomeric pair 106m,gAg in the GDR region is
lower than that in above GDR region. This
means that the isomeric ratio in this work at
the end of the GDR region has to be lower
than that at 30 and 50 MeV obtained by the
authors in [13-15, 17]. This fact confirms that
our results are logical.
It is interesting to note that stable nuclei
In and 107Ag are odd-even ones having the
same nucleon configurations and their spins
are determined by the last odd proton 1g9/2 of
fourth shell 1f7/2, 2p3/2, 1f5/2, 2p1/2, 1g9/2.
Therefore in agreement with the shell model
their spins have to be of the same value i.e. I=
9+/2. However, the experimentally obtained
values of spins for 113In and 107Ag are different
and equal to 9+/2 and 1-/2 respectively. As
result of (γ, n) photonuclear reaction odd-odd
nuclei 112In and 106Ag were formed and their
spins are determined by the mentioned odd
proton 1g9/2 and odd neutron 2d5/2 of the
fifth shell [25]. As a result, isomeric pair
112m,g
In was formed with isomeric and ground
state spins 4+ and 1+ while isomeric pair
106m,g
Ag was formed with isomeric and ground
state spins 6+ and 1+ respectively. It is well
known that the yields of the isomeric and
ground states depend on their spins and the
isomeric ratio depends on the isomeric state
and ground state spins as well as on their
difference. In our case the difference of spins
of the isomeric and ground states is 3 for 112In
and 5 for 106Ag. Therefore the isomeric ratios
in 107Ag(γ, n)106m,gAg and 113In(γ, n)112m,gIn
113
c/ As a principle, the isomeric ratio of an
isomeric pair, produced from different nuclear
reactions depends on the impulse of the
projectiles. This is the influence of reaction
channels on isomeric ratios as demonstrated
45
photonuclear reactions are significantly
different. One can see from [11- 17] for
106m,g
Ag and [1, 2, 27] for 112m,gIn that the
113
isomeric
ratio
in
In(γ,
n)112m,gIn
photonuclear reaction is much higher than that
for 107Ag(γ, n)106m,gAg photonuclear one. It
may be due to that the difference between the
spins of the isomeric and ground states in
106m,g
Ag is bigger than that in 112m,gIn.
IV. CONCLUSIONS
For first time we have completely carried
out the measurement of the isomeric ratios in
107
Ag(γ, n)106m,gAg photonuclear reaction
induced by bremsstrahlung with endpoint
energies in the whole GDR region. The results
provide complete and new data for this region
and could contribute to the Nuclear Data.
This work has been performed at the
Flerov Laboratory of Nuclear Reaction, Joint
Institute for Nuclear Research, Dubna, Russia.
The authors would like to express sincere
thanks to the Chemical Department of the
Flerov Laboratory of Nuclear Reaction for
providing the measurement system.
This research is funded by Vietnam
National Foundation for Science and
Technology Development (NAFOSTED)
under grant number 103.04-2012.56.
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46
On the spectroscopy of bremsstrahlungs produced
by an electron accelerator
Tran Duc Thiep1, Nguyen Tuan Khai2,*, Truong Thi An1,
Phan Viet Cuong1, Nguyen The Vinh1
1
Institute of Physics, VAST, 10 Dao Tan St., Ba Dinh Region, Hanoi
2
Institute of Nuclear Science and Technique, VNATOM
*
(Received 15 August 2013, accepted 23 September 2013)
Abstract: Although electron accelerators are equipments which accelerate electron, in fact they are
intense sources of bremsstrahlung photon and neutron beams. Therefore the study on spectroscopy of
bremsstrahlung is of great importance. This work presents the results obtained by the authors about
the energy distribution of bremsstrahlung spectra, the method for determination of bremsstrahlung
photon flux as well as the possibilities for producing neutron and neutron rich radioactive ions beams
for fundamental research and practical applications.
Keywords: Bremsstrahlung- Energy Distribution- Bremsstrahlung Photon Flux- Neutron Producing
I. INTRODUCTION
Recently electron accelerators have been
widely used in different fields of fundamental
research and practical applications [1 - 5].
Although electron accelerators are equipments
which accelerate electrons, in fact they are
intense sources of bremsstrahlung photon
beams. The principle of converting the
electrons in bremsstrahlung can be found in
[6]. The bremsstrahlung photon flux allows us
a) to determine the characteristics of
photonuclear reaction as the cross section and
yield [7 - 9] b) to estimate the possibility of
producing the neutron-rich radioactive
nuclei beam [10, 11] and photon-induced
neutron beam [12, 13] for fundamental
research and c) to determine the sensitivity
of photon activation method [14, 15] and the
possibilities for radiation protection and
shielding [16]. Therefore the study on
spectroscopy of bremsstrahlung is of great
importance.
This work presents the results obtained
by the authors about the energy distribution of
bremsstrahlung spectra, the method for
determination of bremsstrahlung photon flux
as well as the possibilities for producing
neutron for fundamental research and
practical applications.
II. CALCULATION OF ENERGY
DISTRIBUTION OF BREMSSTRAHLUNG
AND THICKNESS EFFECT
The bremsstrahlung produced from
electron accelerators is intense and high
energy photon source. For the experimental
and theoretical calculations on photonuclear
reactions, it is necessary to know its
characteristics as intensity, energy and angular
distributions. The rate of energy dissipation due
to bremsstrahlung and the cross section for its
production are inversely proportional to square
of the mass of the incident particle [17]:
ON THE SPECTROSCOPY OF BREMSSTRAHLUNGS PRODUCED BY…
Where q – the radom number uniformly
distributed between 0 and 1, N- the number of
atoms/cm3,  b - the bremsstrahlung cross
section, which has differential form as follows
[19]:
where m and Z – the mass and the charge of
the particle respectively, Zt – the mass number
of the target. The bremsstrahlung emission is
a dominant energy dissipation mechanism for
electron – the lightest particle, especially at
relativistic energies greater than a few MeV.
Where  – the frequency of photon,
 =
1/137,  = E/ E 0 , E and E 0 - the initial total and
The study on angular distribution of the
emitted bremsstrahlung [17, 18] indicated that
at very low energies of electrons the radiation
intensity is of maximum in direction
perpendicular to the incident beam. However
as the electron energy is increased, the
maximum appears at increasingly forward
angles and at very high electron energies, the
emission of bremsstrahlung essentially occurs
as a narrow pencil in the forward direction,
the average angle of emission is then given by
[18]:
final total energies of electron respectively, 
= 100 mec2h /( E 0 E Z t1 / 3 ), which is quantity
representing effect of screening by the atomic
electrons surrounding the nucleus upon the
near Coulomb field felt by the incident
electron, 1   , 2   - the screening functions
which are usually calculated using a
Thomas- Fermi model of atom [18, 19], f (Zt)
– the small correction to Bohr approximation
which takes into account the Coulomb
interaction of the emitting electron in the
electric field of the nucleus [19]. The all
detailed interactions of electron with the target
can be found in [20]. These interactions have
been included in our calculations in order for
simulating the following processes: a) the
history of the life of electron of an initial
energy T0 hitting a heavy target to its “death”,
where Ee – total energy of electron, me - the
mass of electron and c – the light speed.
When a relativistic electron beam hits a
heavy target, the total energy loss of electron
is summed by two parts as follows:
b) the bremsstrahlung produced and
undergone the characteristic interactions
according to random walks in order to form
the expected energy distribution at the exit of
the target. Fig. 1 presents the typical spectrum
calculated for bremsstrahlung emission at the
exit of W-target of thickness d = 1.1 mm for
Microtron MT-17 of the Institute of Physics,
Vietnam Academy of
Science
and
Technology. Fig. 2 shows the calculated
dependence of the bremsstrahlung intensity on
There is existed so called the critical
energy where the contributions of the above
two dissipation energy mechanisms are
comparable. At energies above this critical
energy bremsstrahlung dominates completely.
Since bremsstrahlung is seen as a production
of another form of radiation than the incident
electron beam, the free path of an incident
electron in the target can be determined as
random walk:
48
TRAN DUC THIEP, NGUYEN TUAN KHAI, TRUONG THI AN,
PHAN VIET CUONG, NGUYEN THE VINH
Table I. Elemental Characteristics and optimum
thickness of some materials
the W-target thickness for T0 = 15 MeV and
the solid points are experimentally measured
data for Microtrons of the Joint Institute for
Nuclear Research Dubna, Russia [21].
Z
Density
[g. cm-3]
Radiation
Length
[cm]
Optimum
Thickness
[cm]
Fe
26
7.86
1.76
0.60
W
74
19.3
0.33
0.12
Pt
78
21.4
0.29
0.11
U
92
18.7
0.31
0.11
Element
III. DETERMINATION OF TOTAL
BREMSSTRAHLUNG PHOTON FLUX BY
ACTIVATION METHOD
In order to determine the total
bremsstrahlung photon flux, we applied the
photon activation method in our experiments.
During the activation process, the number of
radioactive nucleus N (t ) formed at moment t
Fig. 1. The typical spectrum calculated for
bremsstrahlung emission at the exit of W-target for
Microtron MT-17.
can be described as follows:
dN (t )
 N0 E  E   N (t )
dt
(7)
By resolving equation (7) for the case of
activation with bremsstrahlung photon flux
we obtained the following expression for the
number of interested gamma rays irradiated
from the radioactive nucleus:
Fig. 2. The calculated dependence of the
bremsstrahlung intensity on the W-target thickness
for T0 = 15 MeV
S
where
In general, both the simulation and
experimental
date
show
that
the
bremsstrahlung
emission
intensity
approaches a maximum value at a target
thickness of approximately one third of the
radiation length of the materials as
presented in Table I.
mN AI 1  e ti e td 1  e tm  intth
M ( Em  Eth )
(8)
E m - the bremsstrahlung endpoint
energy;  E , Em  - the bremsstrahlung photon
flux at energy E ;  E  - the cross section for
the radioactive nucleus i.e the giant resonance
Em
curve;
th    E , E m dE -
the
Eth
bremsstrahlung photon flux for the region
49
determine  t h . Besides, as mentioned above
from reaction threshold Et h to endpoint energy
E m ;  int =
t h is the bremsstrahlung photon flux for the
Em
  E dE
E
is the integrated cross
region from Eth to E m . However, our purpose
th
section for the same region; S - the area under
the interested photopeak characterizing the
radioactive nucleus i.e the number of gamma
was to determine the total bremsstrahlung
Em
photon flux     E , Em dE i.e for the
0
rays; t m - the measurement time; t i - the
energy region from 0 to E m .
irradiation time; t d – the decay time; m - the
In order to do this, it was necessary to
know
the
energy
distribution
of
bremsstrahlung. The energy distribution of
bremsstrahlung photon flux can be estimated
by the Schiff approximation [22] or
simulation method. In our work we used the
simulation method presented in [23 - 25]. Fig.
3 shows the experimental arrangement and
Table II presents the total bremsstrahlung
photon fluxes at different endpoint energies
by using simultaneous activation of two
monitors Cu and Au in comparison to one
monitor activation [26] and calculated ones
[27]. The more detailed description of this
method can be found in [28].
elemental mass,  - the isotope abundance,
N A - Avogadro number; M - atomic mass; I the gamma ray intensity and  - the detector
efficiency.
The value of t h can be determined from
expression (8) as follows:
th =
1  e
 t i
SM ( Em  Eth )
e td 1  e tm  int mN AI
(9)
In expression (9) all parameters are well
known from literature and experiment except
the integrated cross section  int . Therefore it
is necessary to calculate  int in order to
Al-absorber energy
of low electron
Electron
Accelerator
Monitor Cu
Em
Em
Beam of
accelerated
electrons with
energy Em
Bremsstrahlung
gamma-quanta
Monitor Au
Bremsstrahlung
converter
Fig. 3. Experimental arrangement at Microtron MT – 25
50
Table II. The total bremsstrahlung photon fluxes at different endpoint energies.
Bremsstrahlung
Endpoint
Energy [MeV]
15
18
Total Bremsstrahlung Photon Flux
[Photon.cm-2. s-1. A-1]
This work
References
1.530 x 1013 ± 10%
a)
1.447 x 1013 ± 10%
b)
2.715 x 1013 ± 10%
a)
2.669 x 1013 ± 10%
b)
3.245 x 1013 ± 10%
20
b)
[26]
3.156 x 1013 [27]
22
24
4.946 x 1013 ± 10%
a)
4.797 x 1013 ± 10%
b)
5.628 x 1013 ± 10%
a)
5.498 x 10
13
± 10%
5.540 x 1013 ± 10%
b)
30
6.311 x 1013 [27]
60
1.420 x 1014 [27]
65
a)
3.846 x 1014 ± 10%
measured with Au monitor,
IV. NEUTRON PRODUCTION FROM
PHOTONUCLEAR REACTIONS
FOLLOWING BREMSSTRAHLUNGS AND
TARGET THICKNESS EFFECT
[26]
b)
b)
b)
measured with Cu monitor
Frank Laboratory of Neutron Physics, JINR
Dubna, Russia.
A. Determination of neutron yield
For each tungsten isotope the yields from
(γ, n) and (γ, 2n) reactions are determined by
the simulated bremsstrahlungs and the
reaction cross sections. The photon- neutron
yield Y(γ, xn) from two types of reactions is
the sum of the individual yields. The electron neutron yield is determined by folding
between the calculated bremsstrahlung
spectrum and reaction cross section as
followings:
Electron accelerators are not only intense
sources of bremsstrahlung but also are high
neutron intensity ones. In order to produce
neutron beam photonuclear reactions (γ, xn) or
(γ, xnp) can be used. We have performed a
Monte – Carlo calculation to estimate the
production yield of neutron from the (γ, n) and
(γ, 2n) reactions following the bremsstrahlung
produced by 100 and 200 MeV electron beams
on the tungsten target with thickness from 1.5
to 2.5 mm. for linear electron accelerator of
Y(e, xn) = Y(e, x γ). Y(γ, xn)
51
(10)
where Y(e, x γ) is the electron – photon yield
i.e. production yield of photon obtained from
the interaction of electron with target and
Y(γ, xn) is the photon – neutron yield i.e.
production yield of neutron by photonuclear
reactions.
neutron yields Y(e, xn) at 1.5 mm target
thickness are summarized in Table III. As a
result, the total neutron yields of about (1.01 ±
0.09).10-3 neutron/electron and (1.17 ±
0.11).10-3 neutron/electron were determined
for the cases of using 100 and 200 MeV
electron beams. The more detailed description
of the calculation can be found in [26].
B.
Dependence of the neutron yield on the
target thickness
To consider the dependence of the
neutron yield on the target thickness we have
determined the yield at three values 1.5, 2.0
and 2.5 mm of the thickness for both 100 and
200 MeV. The results presented in Fig. 6
shows a gradual increase of the yield with the
increased target thickness. However it can be
seen that increasing rate is faster in the region
from 1.5 to 2.0 mm compared to that from 2.0
to 2.5 mm, especially for the case of 100 MeV
electron energy. Our calculations have shown
that the electron – neutron yield reaches
maximum at a value which is more or less
equal to 2.0 – 2.2 mm while the electron –
photon yield is still a gradually increasing
function of the thickness in the considered
region from 0.5 to 3.0 mm.
Fig. 4. The simulated bremsstrahlung spectra
produced by 100 (curve 1) and 200 MeV (curve 2)
lectron beams incident on 1.5 mm thickness
tungsten target.
Fig. 5. Bremsstrahlung emission at different
angles for the case of using 100 MeV electron
beam: 1. Total spectrum; 2. from 0 to 5 0; 3. fom 5
to 100 ; 4. From 10 to 150 and 5. From 15 to 200.
Fig. 4 shows the bremsstrahlung spectra
produed by 100 and 200 MeV electron beams
incident on 1.5 mm tungsten target. Fig. 5
shows thr bremtrahlung emission at different
angles for the case of using 100 MeV electron
beam. The obtained results of individual
Fig. 6 Neutron yields as a function of target
thickness at 100 (■) and 200 MeV (●) electron
energies.
52
Table III. Neutron yields at 1.5 mm thickness of tungsten target at 100 and 200 MeV electron beams
Threshold
Energy,
MeV
Neutron Yield
[neutron/electron] at
Ee = 100 MeV
Neutron Yield
[neutron/electron] at
Ee = 200 MeV
W(γ, n)185W
7.19
(1.91 ± 0.13).10-4
(2.16 ± 0.13).10-4
W(γ, 2n)184W
12.95
(1.04 ± 0.09).10-4
(1.17 ± 0.09).10-4
W(γ, n)183W
7.41
(2.21 ± 0.14).10-4
(2.42 ± 0.14).10-4
W(γ, 2n)182W
13.60
(1.11 ± 0.09).10-4
(1.27 ± 0.09).10-4
W(γ, n)182W
6.19
(0.95 ± 0.08).10-4
(1.18 ± 0.09).10-4
W(γ, 2n)181W
14.26
(0.38 ± 0.04).10-4
(0.52 ± 0.05).10-4
W(γ, n)181W
8.07
(1.65 ± 0.12).10-4
(1.87 ± 0.12).10-4
W(γ, 2n)180W
14.75
(1.92 ± 0.07).10-4
(1.13 ± 0.08).10-4
W(γ, n)179W
8.41
(0.009 ± 0.003).10-4
(0.012± 0.003).10-4
W(γ, 2n)178W
15.35
(0.002 ± 0.001).10-4
(0.003 ± 0.002).10-4
Total
(1.01 ± 0.09).10-3
(1.17 ± 0.11).10-3
Abundance, %
186
W (28.60)
Reaction
186
186
184
W (30.70)
184
184
183
W (14.28)
183
183
182
W (26.30)
182
182
180
W (0.12)
180
180
C.
A+ Bsin2θn, with B/A= 2.0 ±0.5 [30]. We
justify this choice by remarking that the
photons which are active in producing
neutrons have energies concentrated above
threshold whatever the electron energy. The
bremsstrahlung radiation is taken to be exactly
forward. The anglular distribution of the
produced neutron is therefore the same as in
[29, 30], while the neutron energy spectrum is
displayed in Fig. 7.
Neutron energy distribution
Besides evaluating the total neutron yield,
the Monte-Carlo method makes it possible to
calculate the energy and angular distributions
of the produced neutrons once the angular
dependence of the photonuclear reaction cross
section is known. In case of the (γ, n) reaction,
the energy-momentum conservation relates the
neutron energy En to its production angle θn
via:
Mr2 = (ΔE + Mn)2 - 2ΔE(En + Mn)
+ 2Eγ [ΔE - En – cosθn (En2 - Mn2)0.5] (11)
where Mr - the mass of the final state nucleus
(c= 1), ΔE= (Mt – Mr – Mn)c2 with Mt being
the mass of the target nucleus, Mn the neutron
mass and Eγ the incident photon energy.
It is needed to note that the neutron
kinetic energy is Tn = En – Mn. The angular
distribution of the photonuclear cross section
is taken from [29, 30]. It has a form P(θn) =
Fig.7. The energy spectrum of neutrons
emitted by the 186W(γ, n)185W reaction.
53
[5] 5. IAEA “Manual on radiation sterilization
of Medical and Biological Materials ”
Technical Report, Series No.149, IAEA,
Vienna 1973.
V. CONCLUSIONS
We have performed the following works:
a. Using the Monte-Carlo simulations to study
the bremsstrahlung distribution emitted as a
result of braking an accelerated relativistic
electron beam by some heavy targets Fe, W,
Pt, U; b. Using the Monte-Carlo simulations to
evaluate the total neutron yields from
photonuclear reactions (γ, n) and (γ, 2n)
induced by bremsstrahlung photons produced
from 100 and 200 MeV electron beams
incident on the tungsten target and c.
Determination of total bremsstrahlung photon
flux by activation method. The obtained
results can be applied for the experimental and
theoretical calculations on photonuclear
reactions as well as for practical applications
including the assessment of photon activation
sensitivity, radiation protection and shielding
and especially for those based on producing
the neutron-rich radioactive nuclei and
photon-induced neutron beams,
[6] Yu. M. Tsipenyuk, The Microtron, (Taylor &
Francis, London and New York, p. 167
(2002).
[7] A. D. Antonov et al, Preprint of the Joint
Institute for Nuclear Research, Dubna,
Russia, P15-89-318.
[8] A. D. Antonov et al, Preprint of the Joint
Institute for Nuclear Research, Dubna,
Russia, P15-90-425.
[9] N. V. Do, P. D. Khue, K. T. Thanh, T. D.
Thiep, P. V. Duan, Y. S. Lee, G. N. Kim, Y.
Oh, H. S.Lee, H. Kang, M. H. Cho, I. S. Ko
and W. Namkung, J. of the Korean Physical
Society V.50, N.2, 417 (2007).
[10] Yu.Ts. Oganessian et al, Preprint of JINR
Dubna, Russia, E7-2000-83.
[11] F. Ibrahim, J. Obert et al, Eur. Phys. J. A 15,
357 (2002).
[12] K. Devan, A H. Meaze, Guinyun Kim,
Young Seok Lee, Hengsik Kang, Moo-Hyun
Cho, In Soo Ko Won Namkung, N.V. Do,
P.D. Khue, T. D. Thiep and P. V. Duan, J. of
the Korean Physical Society V.49, N.1, 89
(2006).
This research is funded by Vietnam
National Foundation for Science and
Technology Development (NAFOSTED)
under grant number 103.04-2012.56.
[13] N. V. Do, P.D. Khue, T.D. Thiep, P.V.
Duan,Y.S. Lee, H.S. Lee, M.H. Cho, I.S. Ko
and Won Namkung, J. of Korean Physical
Society V.48, N.3, 382 (2006).
REFERENCES
[14] R.A. Kuznhetzov, Activation Analysis,
Publisher Atomizdat, Moscow, p. 110 (1974).
[1] U. E. P. Berg and U. Kneissl, Ann. Rev.
Nucl. Part. Sci. 37, 33 (1987).
[15] Yu. N. Burmistenko, Photonuclear Analysis
of
Materials
Compound,
Publisher
Energoatomizdat Moscow, p.59 (1986).
[2] E. Jacobs, H. Thierens, D. De Ferenne et al,
Phys. Rev. C, V. 21, N.1, 237 (1980).
[16] Technical
Report
Series
No.
188
“Radiological Safety Aspects of the
Operation
of
the
Electron
Linear
Accelerators”. IAEA, Vienna 1979.
[3] Yu. P. Gangrski, A. P. Tonchev and N. P.
Balabanov, J. Physics of Particles and Nuclei,
V. 27, N.4, 1043 (1996).
[17] P. Marmier and E. Sheldon, “Physics of
Nuclei and Particles”, V.1, Academic Press,
New York and London, 1969.
[4] C. J. Karzmax, N. C. Pering, Phys. Med. Biol.
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54
[18] J. A. Wheeler and W. E. Land, J. Phys. Rew.
55, 858 (1939).
[25] N.T.Khai, T.D.Thiep et al, J. Phys. of
Particles and Nuclei Letters V.7, N.1, 34
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[19] W. R. Leo, “Techniques for Nuclear and
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55
Contents
Studies of multiparticle photonuclear reactions in natural iron induced by 2.5 GeV
bremsstrahlung
Pham Duc Khue, Kim Tien Thanh, Nguyen Thi Hien ........................................................1
Analysis of steam generator tube rupture accident for Korean reactor APR1400
Le Dai Dien, Le Tri Dan ....................................................................................................7
Design and simulation calculations for one - and two - neutron transfer 24Si(p,d)23Si and
24
Si(p,t)22Si reaction experiment
N.T. Khai, B.D. Linh, L.X. Chung, D.T. Khoa, A. Obertelli, A. Corsi, A. Gillibert, N. Alamanos D.
Sohler, Zs. Dombradi, N. Keeley ................................................................................ 15
Mechanical properties and thermal stability of poly (L-lactic acid) treated by Co-60
gamma radiation
Tran Minh Quynh, Nguyen Van Binh, Pham Duy Duong, Pham Ngoc Lan, Hoang
Phuong Thao, Le Thi Mai Linh ...................................................................................21
Studying agents causing respiratory disease in the airborn at Institute for Nuclear
Science and Technology’s area, in Hanoi
Nguyen Thuy Binh, Vo Thi Anh, Nguyen Thu Ha, Ha Lan Anh, Nguyen Hong Thinh, Do
Thi To Uyen, Pham Quang Thang ....................................................................................29
The isomeric ratios in 107Ag(γ, n)106m,gAg photonuclear reaction induced in the giant
dipole resonance region
Tran Duc Thiep, Truong Thi An, Phan Viet Cuong, Nguyen The Vinh, Bui Minh Hue,
A. G. Belov, O. D. Maslov ...............................................................................................39
On the spectroscopy of bremsstrahlungs produced by an electron accelerator
Tran Duc Thiep, Nguyen Tuan Khai, Truong Thi An, Phan Viet Cuong, Nguyen The Vinh … 47

Nuclear Science and Technology

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