Multiple particle break-up studies in neutron rich Li isotopes

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Multiple particle break-up studies in neutron rich Li isotopes
Multiple particle break-up studies
in neutron rich Li isotopes
M. Madurga
MAGISOL collaboration meeting, January 18-19, 2007
MMF13
β-delayed break-up of 11Li
Qβ=20.4 MeV
T1/2=8.5 ms
3/2-
20.4
11Be
10Be+n
d energy distribution
γ & n →The
0.50 MeV
1974
17.9
11Li
β
may depend on the halo wave
97% function.
9Be+2n
7.31 MeV
1979
Charged
particles
(and n)
→β -strength distribution:
core6He+α+n
and halo components?
7.90 MeV
K Riisager, NPA 616(1997)169
∼0.3%
15.72 MeV
d spectrum
17.91 MeV
n
1996
8.9
2α+3n
7.9
1980
1983
9Li+d
8Li+t
6He+α+n
n
2α+3n
8.98 MeV
‰Better knowledge of BGT of 1980
∼3%9
Li and 11Li is needed
8Li+t
Charged
‰Obtain the
particles
9Li+d
15.7
γ
0
9Be
γ
1/2+
11Be
0.5
3/2-
7.3
0+
10Be
Diapositiva 2
MMF13
El nucleo que estudiamos el 11Li se encuentra junto a la linea de goteo de neutrones, cuyas dos caracteristicas mas notables es la presencia de
un halo dineutronico y la variedad de canales de desintegracíon que presenta. El alto valor de Qbeta hace que todos (mostrar) estos canales
sean energeticamente posibles, con lo que desde el descubrimiento del 11Li se espero obervarlos. Las fechas muestran el año de primera
observacion del canal. Primeos canales, desintegracion beta seguida de gammas y emision de neutron seguida de gammas. Este modo de
desintegracion ha sido muy umportante para estudiar el 10Be. En el segundo grupo tenemos la ruptura de los niveles, tanto secuencial, en
10be como directa
EL ultmo grupo es el de lso 2 canales que no eiten neutrones. Desintegracion del nivekl a 18 MeV de 11Be. El espectro de deuterones es
especialmente interesante para detereminar si la desinegracion es traves de 11be (beta en el core) o directa (beta del halo).
Miguel Madurga Flores; 11/05/2006
MMF14
Experimental set-up
•Charged particle
detection:
•4 DSSSD’s + thick
silicon pads
•Compact cubic
geometry: 4x 4% 4π
•Neutron detection:
•TONERRE time of
flight. 20% 4π
Diapositiva 3
MMF14
Miguel Madurga Flores; 06/02/2006
Break-up of the 2.43 MeV state
Eα (coincidences)
Eα Eα En vs Esum
ƒ7% branch to 8Be(gs)
E(9Be)=1.57+Esum
D.R. Tilley et al., NPA 745(2004)155
ƒProposed decay through 8Be(2+)
Y.S. Chen et al., NPA 146(1970)136
Y. Prezado et al., PLB 618(2005)43
Monte-Carlo simulations
R-matrix formalism
Γ ( e' ) / 2
2 low energies
P (e − e' ) / at
Detector efficiency
2
2
) − ( Γaccount
/ 2) (e0 '− Δ − e' ) 2 − ( Γ( e' ) / 2) 2
has to be(etaken
0 − Δ − einto
w( e, e' ) = f β (Qβ − e)
O.V. Bockarev et al., NPA(505)(1989)215
Hyper-spherical
harmonics
L=3
DSSSD2
Neutron TOF spectrum
PRELIMINARY
8Be(2+)
200
5He(gs)
1000
β
600
n
400
10
4
10
3
10
2
Low gate
Direct
DSSSD2 gated
n(tof)-spectrum
800
180
160
140
120
100
80
60
40
20
0
Zone 1: 200Æ350 keV
Zone 2: 760Æ5650 keV
0
100
200
300
400
500
140
120
High gate
100
10
80
200
60
1
0
1000
2000
3000
4000
5000
6000
40
20
0
0
100
200
300
400
500
0
0
100
200
300
400
500
Core+Halo decay
•Obtain the 11Li BGT distribution
at energies above 10.6 MeV.
?
H.O.U. Fynbo, NPA 736(2004)37
M.J.G. Borge et al. NPA 613 (1997) 119
BGT known from
•Comparison
withβ-γ-n
the 9Li
experiments
distribution.
MMF3
β-delayed charged particle emission
11Li
Coincidence spectra
M. Langevin et al.,
NPA 366(1981) 449
EvsE plot
Sum spectrum
Diapositiva 8
MMF3
In the plot is show the data in the back to back geometry.
It is clearly seen between the two black lines the three body decay through an intermediate state.
If we take now all data and project the sum energy of the two charged particles we get an spectrum similar to the one obtained 25 years ago,
expected as langevin had two detectors in close geometry as we have in our set-up.
The two main peaks, coincide with the following regions (show) in the e vs e spectrum.
Miguel Madurga Flores; 06/02/2006
α-α & α-6He resonance states
¾No evidence of feeding the 8Be(gs)
or 8Be(2+).
α-α
¾The high energy peak corresponds
to the 9.5 MeV state in 10Be
E(10Be)= E(α-6He)+7.4
α-6He (MeV)
α-6He
α-α in 9Be
700
600
500
400
300
gs
2+
200
100
α-α (MeV)
0
0
1
2
3
4
5
6
MMF1
11Be
break-up: Charged particle
coincidence spectrum
-M. Langevin et al.,
NPA 366(1981) 449
-M.J.G. Borge et al.
NPA 613 (1997) 119
Diapositiva 10
MMF1
En el esquema de niveles se muestra en rojo los niveles que Langevin propone para explicar el esspectro suma. Los dos picos corresponden a
la desintegracion de un nivel estrecho a 9.4 MeV en 10Be, canal a 3 particulas y canal a 5 pariticulas, mientras que el fondo suave
correspondera a la desinegracion directa a 5 particulas del nivel a 18 MeV en 11Be. Nuestro objetivo es corroborar esta afirmacion, pero
incluyendo una descripcion mas precisa mediate simulaciones.
Miguel Madurga ; 07/12/2006
Break-up of 11Be(18.5)
10
3
10
2
10
SIMULATION
DATA
α+6He+ n
2α+3n
¾Breitt-Wigner shape (fermi
function included): Γ=200 keV
¾Excellent agreement with the
sum spectrum
1
0
2
4
6
8
10
12
¾EvsE scatter plot poorly
reproduced
The 7He channel
9The shape hints mass-7/mass-4
involvement
P2 m2 P2 m2
E1 =
=
= E2
2m1 m1 2m2 m1
M. Meister et al. PRL 88(2002)102501
7/4
4/7
α-6He-n Break-up through 7He(gs)
R-matrix formalism
7/4
10
3
9Scatter plot shape
4/7
9High energy end of
sum energy spectrum
10
2
10
1
0
2
4
6
8
10
12
7He
and 11Be spectra analysis
14
6HeÅÆα
12
10
8
→The 6He-α relative energy indicates
low (if any) presence of the first two
states in 7He decaying into 6He+α
6
E(11Be) MeV
4
2
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
→The
exctitation spectrum
implies that the 18.5 MeV
state do not
11Be
decay through low-lying states in 7He
11Be
E 11 Be = Eoffset
⎛ m + m2 ⎞ 2
⎟⎟ P
+ ⎜⎜ 1
⎝ 2m1m2 ⎠
⎛ m2 ⎞
⎟⎟ E1
E 11 Be = Eoffset + ⎜⎜
⎝ m1 + m2 ⎠
20
17.5
15
12.5
10
7.5
Eoffset=8Æ9.28 MeV
5
2.5
α-6He
0
13
14
15
16
17
18
19
2α3n Break-up through 7He
¾Test of different
mechanisms
2α3n
break-up
¾The EvsE scatter plot shape do not
match the experimental data
Summary and conclusions on the
break-up of the 18.5 MeV state
• Pure phase-space decay cannot explain
the EvsE scatter plot
• The shape of the EvsE scatter plot hints
possible role of 7He intermediate states
– The E(11Be) rules out the 7He channel in the
6He-α-n decay of the 18.5 MeV state.
– Possible decay of lower energy states?
– R-Matrix formalism not appropriate?
MMF9
Break-up of 11Be(10.5)
10
3
Simulated channels (red=sum)
11Be*(10.56)Æ10Be*(9.48)+nÆ6He+α+n
10
11Be*(10.56)Æ10Be*(9.48)+nÆ2α+3n
2
10
1
0
2
4
6
8
10
12
Diapositiva 17
MMF9
with this data we performed a simulation with the known alpha-alpha and 6he and alpha channels.
in ths data we can see the contribution through the 9.5 meV level into 6he+alpha, and the decay of this level into 4 particles.
on the contrary the break-up into 5 particles of the 18.15 level in 11be is this broad (show) distribution.
Miguel Madurga Flores; 06/02/2006
Energy reconstruction problems
40000
E(6He) E(α)
20000
35000
17500
30000
15000
25000
12500
20000
10000
15000
7500
10000
5000
5000
2500
0
0
200
400
600
800
1000
1200
1400
1600
0
1800
E(6He) E(α)
¾Particle identification based
on energy discrimination.
E(6He)<E(α)
0
500
1000
7000
1500
2000
2500
1400
E(11Be)
6000
1200
5000
1000
4000
800
3000
600
2000
400
1000
200
0
9.4
9.6
9.8
10
E(11Be)
10.2
10.4
10.6
10.8
11
11.2
0
Low energy tail!
10.5
11
11.5
12
12.5
MMF19
The 6He+α+n channel
Non-interfering Multiple-level
single-channel R-matrix
formalism
w(e, e' ) = f β (Qβ − e)
P (e − e' ) / 2
Γ (e' ) / 2
(e0 − Δ − e) 2 − (Γ / 2) 2 (e0 '−Δ − e' ) 2 − (Γ(e' ) / 2) 2
11Be excitation energy
10Be excitation energy
Parameters:
ln=11
Γ(e)=2P(e)γ2
γ2(10.56) = 0.210 MeV2
γ2(9.48) = 0.045 MeV3
45
140
40
120
35
100
30
80
25
20
60
15
40
10
20
0
1 Y. Hirayama et al., PLB 611(2005)239
2. F. Ajzenberg-Selove et al., PRC 17(1978)1283
3. D.R.Tilley et al., NPA 745 (2004) 458
5
9
9.2
9.4
9.6
9.8
0
10
11
12
13
14
Diapositiva 19
MMF19
using two resonances in the single-channel aproximation of R-matrix theory
The transition probablity depends on the
The fitting for the 9.5 MeV sate in 10Be is good, and if we implement the neutron energy to reconstruct the 11be energy the fit is not as good
and we can see a contribution at high energies that must be due to feeding from levels at energies above the 10.6 considered in this analysis.
Miguel Madurga Flores; 06/02/2006
New decay simulations
45
45
45
120
What can we do?
E(11Be)
40
4040
1. Increase the level’s width.
¾ reasonable agreement
2. Add new levels.
¾ Ratio adjusted to
reproduce the shape
100
35
3535
30
3030
80
2525
25
60
2020
20
1515
15
40
11.4
1010
10
5
0
20
55
000
9.5
10.6
10
10.5
11
10 10
11
10
11
11
11.5
12
12
12
12.5
13
1313
13
13.5
141414
14
15
85%
1.4 MeV
More levels?
15%
1.4 MeV
11Be
n
9.5
10Be
Summary
•
Objectives:
•
9Li
– Complete the knowledge about the 9Li and 11Li β-decay.
– Study the β-delayed 11Li d spectrum.
β-decay
– The simulated alpha coincidence and singles spectra favor the
democratic break-up described by hyper-spherical harmonics (L=3) of
the 2.43 MeV levl in 9Be.
– The preliminary analysis of the neutron tof spectrum favors the
sequential decay through the tail of the first excited state in 8Be
•
11Li
β-decay
– Decay of the 18.5 MeV state in 11Be: The pure phase-space break-up
cannot explain the EvsE scatter plot. The shape hints the role of 7He
resonances, although no direct evidence of 6He-α-n break-up is found
– Decay through the 10Be 9.5 MeV resonance: The simulations indicate
the role of a 11.4 MeV level in 11Be.
β-delayed break-up of 9Li
Y. Prezado et al., PLB 618(2005)43
9LiÆ9BeÆ2α+n
•Successfully determined
spin and parity of levels y
9Be.
•New level at 5 MeV
determined
•Break- up of the 2.43 MeV
not thoroughly studied
ƒ7% branch to 8Be(gs)
D.R. Tilley et al., NPA 745(2004)155
ƒProposed decay through 8Be(2+)
Y.S. Chen et al., NPA 146(1970)136
Astrophysical interest: α(αn,γ)9Be
and 9Be(α,n)12C
5/2-
11.2 MeV
1/2-
8.9 MeV
3/2-
8.4 MeV
α
7He+α
n
7.9 MeV
6He+α+n
5/2-
11.2 MeV
3n
α
9.7 MeV
2+
1/2-
8.9 MeV
3/2-
8.4 MeV
7He+α
2n
3n
8.9 MeV
α+3n
n
7.9 MeV
6He+α+n
11.4
1.4 MeV
10.4
n
11Be
9.5
10Be

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