Underground nuclear astrophysics

Transcription

Helmholtz International Summer School
"NUCLEAR THEORY AND ASTROPHYSICAL APPLICATIONS"
Dubna, July 21 - August 1, 2014
Tamás Szücs for the LUNA collaboration
Dr. Tamás Szücs | Institut for Radiation Physics | [email protected] | www.hzdr.de


Nuclear reactions building up the material of our universe
Charged particle induced reaction
 Thermal movement
 Coulomb barrier
 Typical energy region

Signals in a typical measurement
 Peak area determination
 Confidence limits

Background
 Sources
 Reduction techniques

Importance of the underground measurements
 Typical background underground
 Push the limits

Page 2
Planned upgrade of LUNA and other sites
Member of the Helmholtz Association
Tamás Szücs | [email protected] | NTAA Summer School, Dubna, 21.07.-01.08.2014


 Coulomb barrier


Background
 Sources

 Push the limits

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Origin of the chemical elements
C+Si
burning
r-, s-, pprocesses
H+He
burning
Big Bang
2
3
4
5
20
30
40
50
Charged particle induced reactions
Page 4
Rate
Hydrogen burning in stars: pp-chain, normal and hot CNO-cycle
Page 5
An age of precision for solar neutrinos from the pp-chain
BPS 2008 solar model
Borexino, SNO+
SNO, SuperK
Nuclear data must match the
precision of -astronomy:
Water-Cherenkov detectors, assuming large neutrino mixing angle:
4% precision
5% precision
Page 6
for solar 8B neutrino flux (SNO, SuperK) [B. Aharmim et al., PRC 87, 025501 (2013)]
for solar 7Be neutrino flux (Borexino) [G. Bellini et al., PRD 89, 112007 (2014)]
The proton-proton chain
Impact of cross section on neutrino
flux Be and B from model:
Borexino, SNO+
BeBe
BB
3He(3He,2p)4He
2.2%
2.1%
3He(,)7Be
4.6%
4.3%
--
7.7%
Reaction
SuperK, SNO
7Be(p,)8B
Before LUNA it was 7.5%
A. Serenelli et al., Phys. Rev. D 87, 043001 (2013)
Page 7


 Coulomb barrier


Background
 Sources

 Push the limits

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Nuclear reaction cross section (s) for charged particles
• Typical Coulomb barrier height : ~ MeV
• Typical temperature kB * T ~ keV
 The energy dependence of the cross
section is dominated by the tunneling
probability.
Tunneling probability
(for relative angular momentum l=0):


 exp  Z1Z 2 

E


Thermal neutron capture: ~1 barn
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Charged-particle capture at
astrophysical energies: s ~ 1 nanobarn!!
“NANO - ASTROPHYSICS”
How much is the astrophysically relevant energy?
The Gamow peak
Maxwell-Boltzmann
velocity distribution
Tunneling probability
(for zero relative angular
momentum):
Page 10


 exp  Z1Z 2 

E


The Gamow peak, some examples
Scenario
Reaction
EG[keV]
s [barn]
Detected
events/hour
Sun (16 MK)
3He(,)7Be
23
10-17
10-9
14N(p,)15O
28
10-19
10-11
AGB stars (80 MK)
14N(p,)15O
81
10-12
10-4
Big bang (300 MK)
3He(,)7Be
160
10-9
10-1
2H(,)6Li
96
10-11
10-3
1 barn= 10-24 cm2; assume 1016 s-1 beam, 1018 at/cm2 target, 10-2 detection efficiency
Extrapolations seem to be necessary.
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Extrapolation and the astrophysical S-factor
3
He,   Be
7
1  2
sE   e
SE 
E
Geometrical
cross section
s-wave Coulomb
Barrier transmission

2  Z1Z 2 
E
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 Coulomb barrier
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Background
 Sources
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 Push the limits
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Typical signal
Relative error of the peak area:
S
S
B
Page 14
S
1

S
S
S  2B
1 2B

 2
S
S S
Confidence limits
Critical limit:
L C  k 2B
Detection limit:
L D  k  2k 2B
2
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 Coulomb barrier
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Background
 Sources

 Push the limits

Page 16
What contributes to the laboratory background?
Energetic muons
Radioisotopes in
the laboratory:
238U - daughters
232Th - daughters
40K
Passive shield
Detector
Neutrons created in the
passive shield or
laboratory walls by
muons (,n)
Red:
Radioisotopes in
detector and shield:
238U - daughters
232Th - daughters
60Co
Neutrons from outside:
- cosmic ray
- (,n) in rock
E < 3 MeV
Green: E < 3 MeV and E > 3 MeV
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Laboratory background at the Earth’s surface
Natural radioisotopes
Page 18
Cosmic-rays, mainly muons
Laboratory background at the Earth’s surface using passive shield
HPGe spectra recorded at the
surface of the Earth:
Black, no shield
Red, commercial lead shield
Typically ~1 count/hour laboratory background in HPGe spectra at E> 3 MeV
Lead does not do much at E> 3 MeV. Help!!!
Page 19
Laboratory background at the Earth’s surface using active shielding
Factor of 10 – 100 reduction at E> 3 MeV
Is it not enough?
Page 20
Why to go underground, an example
Scenario
Reaction
EG[keV]
s [barn]
Detected
events/hour
AGB stars (80 MK)
14N(p,)15O
81
10-12
10-4
1 barn= 10-24 cm2; assume 1016 s-1 beam, 1018 at/cm2 target, 10-2 detection efficiency
Without background, for 10% precision one need 100 counts. With this count rare it
would take 115 years. This is practically impossible.
BUT approach as close as possible: Consider 100 times higher rate. (10-2 event/h)
Background
count rate
(event / hour)
Without background
Time needed to
reach 10% precision
(years)
0
1.1
Typical overground settings with active shield
2*10-2
3.4
Deep underground
4*10-4
1.2
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Attenuation of the laboratory background underground
Surface
Felsenkeller/DE
Gran Sasso/IT
The issues are:

Energy loss of passing muons
in the detector
 Active shield
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Interaction of cosmic-ray
nucleons in the detector
 10m rock

(,n) neutrons from natural
radioactivity in the walls
 Passive shield

Neutrons generated by muons
 500m rock
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
 Coulomb barrier


Background
 Sources

 Push the limits /The 3He(,)7Be reaction/

Page 23
Laboratory background for E > 3 MeV
Deep underground the background count rate is 3 order of magnitude lower at E> 3 MeV
What about the lower energies?
Page 24
Laboratory background for E < 3 MeV
E = 1.5 MeV
Earth’s surface:
4 counts/hour
Shallow, ~110 mwe:
0.13 counts/hour
Gran Sasso, ~3800 mwe:
0.007 counts/hour
Page 25
LUNA 0.05 MV accelerator, 1992-2001
•
•
50 kV accelerator deep underground
Direct experimental data ruled out a possible
nuclear solution for the solar neutrino problem
Solar Gamow peak covered with data
•
3He(3He,2p)4He
cross section
Claus Rolfs
LUNA 50 kV
accelerator
Page 26
LUNA laboratory at Gran Sasso / Italy
LUNA-MV,
under
preparation
~140 km from Rome
1000 m above sea level
1992-2001
Easy access (motorway)
2000-2014+
Italian national
laboratory
~100 local staff
~1400 m rock
Page 27
106 µ-reduction
103 n-reduction
~600 external users
The LUNA 0.4 MV accelerator
LUNA approach:
Measure at or near Gamow peak, using
• high beam intensity
• low background
• great patience
Page 28
The LUNA beam lines
Page 29
Underground -counting
facilities
In-beam -spectroscopy
underground
Rock
Closed passive shield
Activated
sample
Detector
Open passive shield
Rock overburden
attenuates cosmics: n, µ,
Target
(µ,n)
Beam
Passive
shield
attenuates
Passive
shield
radionuclides in the
laboratory
Detector
Anti-radon flushing with
“old” air/nitrogen
Activation at an accelerator
e.g. at the surface of the Earth,
-counting underground
Page 30
The proton-proton chain
Impact of cross section on neutrino
flux Be and B from model:
Borexino, SNO+
BeBe
BB
3He(3He,2p)4He
2.2%
2.1%
3He(,)7Be
4.6%
4.3%
--
7.7%
Reaction
SuperK, SNO
7Be(p,)8B
Before LUNA it was 7.5%
A. Serenelli et al., Phys. Rev. D 87, 043001 (2013)
Page 31
3He(,)7Be:
How does it work?
Measuring the promptly emitted -rays,
so-called prompt- approach:
S(0) = 0.507±0.016
(Adelberger et al., Rev. Mod. Phys. 1998)
Measuring the created 7Be activity,
so-called activation approach:
S(0) = 0.572±0.026
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3He(,)7Be
at LUNA (activation and prompt- technique)
Windowless 3He gas target,
with 3He recirculation
Page 33
3He(,)7Be
Page 34
at LUNA, in-beam -spectra
3He(,)7Be
at LUNA, 7Be activation spectra
Detected 7Be activities: 0.8 - 600 mBq
Page 35
3He(,)7Be
Page 36
at LUNA, systematic uncertainty
-efficiency
1.8%
Beam intensity
1.5%
Target density
1.5%
7Be
0.7%
losses
Systematic uncertainty, activation
3.0%
Systematic uncertainty, prompt-
3.6%
3He(,)7Be
at LUNA, S-factor results
Sun, 16 MK
Big Bang, 300-900 MK
Page 37
Impact of the 3He(,)7Be data:
More precise inputs for solar 7Be, 8B neutrinos
Impact of cross section s on
neutrino flux Be from model:
Reaction
BeBe
3He(3He,2p)4He
2.2%
3He(,)7Be
4.6%
7.5%
was
before
BUT now
2.5%
needed
Borexino, SNO+
SuperK, SNO
Page 38
Solar neutrino fluxes: Data and model predictions
Neutrino fluxes:
Standard Solar Model;
Antonelli et al., 1208.1356
GS98 = Old, high CNO
elemental abundances
AGSS09 = New, low CNO
elemental abundances

7Be, 8B:

13N, 15O:

Need smaller error bars for the models!
Data more precise than the models
No data yet, but models are not very precise
Slide 39
Daniel Bemmerer | HK 49.1: Underground nuclear astrophysics in Europe | DPG, 20.03.2014 | http://www.hzdr.de
Impact of the 3He(,)7Be data:
No solution for lithium puzzle of Big Bang nucleosynthesis
7Li,
big bang
Big bang production
3He(,)7Be*
 7Li
2H(,)6Li
Observations:
Asplund et al. 2006
Big bang abundances: Serpico et al. 2004
6Li,
Page 40
big bang
LUNA 0.05 MV + 0.4 MV science program for astrophysics
Machine
Reaction
Astrophysics
50 kV (1991-2000)
3He(3He,2p)4He
pp-chain
2H(p,)3He
pp-chain
3He(,)7Be
pp-chain, big bang
14N(p,)15O
CNO cycle
15N(p,)16O
CNO cycle II
25Mg(p,)26Al
MgAl cycle
23Na(p,)24Mg
NeNa cycle
2H(,)6Li
big bang
17O(p,)18F
CNO cycle III
17O(p,)18F
CNO cycle III
18O(p,)19F
CNO cycle IV
18O(p,)19F
CNO cycle IV
22Ne(p,)23Na
NeNa cycle
400 kV (2001-2014)
Page 41
complete
running
LUNA 0.4 MV science program for astrophysics until 2018
Reaction
Astrophysics
12C(p,)13N
CNO cycle
13C(p,)14N
Page 42
2H(p,)3He
big bang
6Li(p,)7Be
big bang
22Ne(,)26Mg
s-process
13C(,n)16O
s-process
Complemented and
extended by the MV machine
LUNA collaboration
Italy
Genova
F. Cavanna, P. Corvisiero, F. Ferraro, P. Prati
Gran Sasso
A. Best, A. Formicola, S. Gazzana, M. Junker, L. Leonzi, A. Razeto
Milano
A. Guglielmetti (LUNA spokeswoman), D. Trezzi
Napoli
G. Imbriani, A Di Leva
Padova
C. Broggini, A. Caciolli, R. Depalo, R.Menegazzo
Roma
C. Gustavino
Teramo
O. Straniero
Torino
G. Gervino
Hungary
Debrecen
Z. Elekes, Zs.Fülöp, Gy. Gyürky, E. Somorjai
Germany
Bochum
C. Rolfs, F. Strieder, H.-P. Trautvetter
Dresden
D. Bemmerer, T. Szücs, M. Takács
Edinburgh
M. Aliotta, C. Bruno, T. Davinson, D. Scott
UK
Page 43
Further reading (incomplete list)
•
Textbooks:
–
–
•
Review articles:
–
–
•
C. Rolfs and W. Rodney: Cauldrons in the Cosmos. University of Chicago Press 1988.
C. Iliadis: Nuclear Physics of Stars. Wiley-VCH 2007.
C. Broggini, D. Bemmerer, A. Guglielmetti, and R. Menegazzo:
LUNA: Nuclear Astrophysics Deep Underground.
Annual Review of Nuclear and Particle Science 60, 53-73 (2010)
H. Costantini, A. Formicola, G. Imbriani, M. Junker, C. Rolfs, and F. Strieder:
LUNA: a laboratory for underground nuclear astrophysics.
Reports on Progress in Physics 72, 086301 (2009)
Paper series about the background:
–
D. Bemmerer et al. (LUNA collaboration):
Feasibility of low-energy radioactive capture experiments at the LUNA underground accelerator facility.
European Physical Journal A 24, 313-319 (2005)
– A. Caciolli et al. (LUNA collaboration):
Ultra-sensitive in-beam -spectroscopy for nuclear astrophysics at LUNA.
– T. Szücs et al. (LUNA collaboration):
An actively vetoed Clover -detector for nuclear astrophysics at LUNA.
– T. Szücs et al.:
Shallow-underground accelerator sites for nuclear astrophysics: Is the background low enough?
European Physical Journal A 48, 8 (2012)
Page 44
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
 Coulomb barrier


Background
 Sources

 Push the limits
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Page 45
The European perspective

1st Workshop on “Underground nuclear-reaction experiments for astrophysics and applications”,
Dresden/Germany April 2010: 30 participants from 8 countries, all projects represented
http://www.hzdr.de/felsenkeller
”Due to the extensive science programme, the long running time per experiment, and the number of
researchers involved (...), most participants see it necessary to call for at least two European
underground facilities to be realized. (...) A consensus emerged that all facilities should be as open as
possible to the community (...). The observational and computational astrophysicists should be included
at the earliest stage, helping drive and define the science agenda and creating the added value of
multidisciplinarity (...)”.

NuPECC Long Range Plan 2010, released on 8 December 2010:
http://www.nupecc.org
“An immediate, pressing issue is to select and construct the next generation of underground accelerator
facilities. Europe was a pioneer in this field, but risks a loss of leadership to new initiatives in the USA. Providing
an underground multi-MV accelerator facility is a high priority. There are a number of proposals being developed
in Europe and it is vital that construction of one or more facilities starts as soon as possible.”

“Round Table LUNA-Megavolt at Gran Sasso”, Gran Sasso/Italy 10.-11.02.2011

3rd workshop on “Underground nuclear-reaction experiments for astrophysics and applications”
Canfranc/Spain, April 2012

„Starting-up the LUNA MV collaboration”, Gran Sasso/Italy 06.-08.02.2013
Page 46
Science case for a higher-energy accelerator underground (1)
Reactions providing the
neutrons for the
astrophysical s-process
•
•
13C(,n)16O
Stellar helium burning
• 12C(,)16O
• 14N(,)18F
• 15N(,)19F
• 18O(,)22Ne
22Ne(,n)25Mg
Carbon burning
• 12C(12C,)20Ne
Heil et al. 2008
Page 47
Science case for a higher-energy accelerator underground (2)
Solar composition problem
• 3He(,)7Be, E>0.4 MeV
• 14N(p,)15O, E>0.4 MeV
Radionuclides seen in space
• 26Al, 44Ti, 60Fe
Applied physics
• 1H(15N,)12C, hydrogen depth profiling
• Proton-induced -emission (PIGE)
Page 48
Gran Sasso / Italy: LUNA-upgrade 3.5 MV accelerator, site identified
Idea: 3.5 MV single-ended
accelerator, with ECR ion
source.
LUNA
0.4 MV
LUNA
3.5 MV
Courtesy A. Guglielmetti
Page 49
Canfranc / Spain
600 m2 (40x15x12)
150 m2 (15x10x7)
Depth:
800 m
Muons: 0.2 to 0.4 x 10-2 m-2 s-1
Ventilation:
11.000 m3/h
Courtesy L. Fraile
Page 50
Facility outside Europe: CASPAR @ Homestake / USA
Aggressive
time line:
Installation
complete by
mid-2015
•
•
•
•
•
Relocation of Notre Dame 1 MV accelerator
Effective energy range ~ 150 keV – 1 MeV
Beam production in range of 100 – 150 µA
protons and alphas
Current plan for refurbishment and upgrade
Recirculating windowless gas target
Courtesy D. Robertson, M. Wiescher (Notre Dame)
Page 51
Surface
Felsenkeller/DE
Gran Sasso/IT
The issues are:

in the detector
 Active shield
Page 52

 10m rock

 Passive shield

 500m rock
Using an active shielded detector underground
Surface
Felsenkeller/DE
One and the same Clover type
HPGe detector with BGO veto
Gran Sasso/IT
Page 53
Felsenkeller / Germany, 47 m deep underground laboratory
•
•
•
ice cellar of former Felsenkeller brewery,
5 km from Dresden city center
-counting facility founded in 1982
Activation studies for nuclear astrophysics
14N(p,)15O, 12C(,)16O
Factor of 2.3
difference
T. Szücs et al, EPJA 48, 8 (2012)
Page 54
Surface
Felsenkeller/DE
Gran Sasso/IT
Freiberg/DE
Page 55
The issues are:

in the detector
 Active shield

 10m rock

 Passive shield

 1000m rock
Freiberg mine / Germany
90m
150m
Klimakammer
230m
Freiberg
Page 56
• Silver mine founded in 1168
• Recently a Teaching, Research and
Visitor Mine
• TU Bergakademie Freiberg
Freiberg mine / Germany
Page 57
High energy background comparison with the Clover detector
Free running spectra
Page 58
High energy background comparison with the Clover detector
Escape suppressed spectra
Page 59
Why not place a used accelerator in Felsenkeller?
Access from outside
Tu
n
nel
IX
n
Tu
ne
lV
III
I
II
lV
ne
V
el
nn
Tu
n
Tu
d new
lab
5MV
Plann
e
N EC
el V
l IV
n
Tun
ne
Tun
Tunnel III
Tunnel II
Tunnel I
Ion
source
i
ist
Ex
ng
u
co
γin g
nt
la b
20 m
Page 60

Industrial area (former Felsenkeller brewery)

Additional space available underground
Felsenkeller, muon flux measurement

Rock overburden 130 m.w.e., slightly
higher than in the nearby existing lowactivity lab (110 m.w.e.)
Courtesy László Oláh
Page 61
Felsenkeller shallow-underground accelerator laboratory
for nuclear astrophysics
12 year old 5MV Pelletron
system from York/UK
MC-SNICS 134 sputter ion
source



12 July 2012: Still assembled, in York
Proposed location underground
100 µA C- beam
100 µA H- beam
No useful He- beam
Home made RF ion source
to be mounted to the
terminal


100 µA H+ beam
100 µA He+ beam
24 July 2012: Loading of components in York
30 July 2012: Unloading of last component in Dresden
Page 62
Carbon-nitrogen-oxygen (Bethe-Weizsäcker) cycle: 14N(p,)15O
Bottleneck
Postulated in 1938
•
Slowest reaction: 14N(p,)15O
•
Some of the oldest observed
stars burn mainly by CNO
•
~0.8% contribution in our Sun
CNO neutrinos as a probe of the
concentration of carbon and
nitrogen in the solar core
Page 63
14N(p,)15O,
how does it work?
Some possible experimental approaches:
(755)%
1.
Study capture to each level separately with
HPGe detector (~1% efficiency), then
extrapolate in the R-matrix framework
2.
Study the total cross section with a summing
crystal (~70% efficiency) directly at relevant
energies
3.
Concentrate on the most uncertain
component (ground state capture) with
precision data and R-matrix fit
4.
Complete the data base over a wide energy
range
5.
Study ground state capture with indirect
methods
(51)%
(51)%
(1515)%
Page 64
14N(p,)15O,
experiment with a summing detector
4 BGO summing crystal
Page 65
14N(p,)15O,
total S-factor from three LUNA experimental campaigns
Schröder et al. 1987
LUNA 2004-2006-2008
TUNL 2005
total
only 15O(GS)
Page 66
LUNA divided the 14N(p,)15O cross section by 2!
Capture to...
NACRE compilation
1999
LUNA, phase 1
2004
TUNL
2005
LUNA, phase 3
2008+2011
...ground state in 15O
1.55  0.34
0.25  0.06
0.49  0.08
0.27  0.05
...excited states in 15O
1.65  0.05
1.36  0.05
1.27  0.05
(1.39  0.05)
3.2  0.5 (tot)
1.6  0.2 (tot)
1.8  0.2 (tot)
1.66  0.12 (tot)
S(0) in keV barn
Adelberger et al.
2011
recommended
precision 7%...
M. Marta et al.,
Phys. Rev. C 83, 045804 (2011)
...but it should be
further improved!
Slide 67
Daniel Bemmerer | Underground accelerators | ATHENA final workshop, 15.05.2014 | http://www.hzdr.de
Astrophysical implications of the LUNA 14N(p,)15O data
14N(p,)15O
cross section cut in half!
S(0) = 3.2 keV barn (1998)
 1.66±0.12 keV barn (2011)
1.
Independent lower limit on the age of the universe, through turnoff luminosity of main
sequence stars in the oldest globular clusters: 14±2 billion years.
2.
CNO contribution to solar burning reduced by a factor 2, now 0.8% of energy production.
3.
More efficient dredge-up of carbon to the surface of asymptotic giant branch stars.
4.
A chance to now measure carbon+nitrogen content of solar core with neutrinos.
Page 68
Age determination of very old stars (in globular clusters)
 Hertzsprung-Russel diagram, turnoff of globular cluster stars from the main sequence
 Lower CNO rate leads to higher derived age for a given globular cluster
How to measure the age of a star cluster:
https://www.e-education.psu.edu/astro801/content/l7_p6.html
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Study of 14N(p,)15O over a wide energy range
Solar Gamow peak
Important levels in 15O
•
E = -0.504 MeV, 15O*(6.79)
•
E = 0.259 MeV
•
E = 0.987 MeV
•
E = 2.187 MeV
•
“background pole”
Curves:
R-matrix
extrapolations
Münster 1987
LUNA 2004
TUNL 2005
Page 70
HZDR 2008-
Experimental setups at the HZDR Tandetron, Dresden
Page 71
High-energy data on the 14N(p,)15O reaction
•
•
Preliminary data from the Dresden 3 MV Tandetron
Also high-energy data influence the R-matrix extrapolation to low energy
Page 72
Doppler shift study of the lifetime of the 6.792 MeV level in
E  (6792) 
0.9 eV =
15O
 (6792)
0.7fs

•
•
Page 73
Subthreshold level populated in d(14N,n)15O reaction
Difficult analysis, expected lifetime ~1 fs
Nuclear Resonance Fluorescence study of the level widths in
15N
15N)
Page 74
15N
SE
15N
15N
16O 11B
SE
SE SESE
11B
16O
SE
15N 15N
11B
SE SE SE
SE
SE
15
15N N
SE
SE
15N
15N
SE
SE
Page 75
15N
15N
15N
Page 76
15N
Summary
Page 77

Underground nuclear astrophysics

Transcription

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