Transcript Document 7435658

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CSIC
Grupo de Física
Nuclear Experimental
Decay Studies @ EURISOL
María José García Borge
Instituto de Estructura de la Materia, CSIC
Florence, 13-18 January 2008
M.J.G. Borge, IEM, CSIC, Madrid (Spain)
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Grupo de Física
Nuclear Experimental
Overview
Desintegration +-EC
Desintegration Desintegration 
Fission
Halo structure
Disappearance of magic
numbers
Exotic decays
Near the drip lines
Florence, 13-18 January 2008
 Asymmtries
Order to Chaos
M.J.G. Borge, IEM, CSIC, Madrid (Spain)
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Grupo de Física
Nuclear Experimental
 Global
Decay properties of exotic nuclei
properties
• Short half-lives (ms)
1916
Rutherford & Wood  [Philos. Mag. 31 (1916) 379]
1963
Barton & Bell identified 25Si as p
• High Q values
• Low Sp/n values
-delayed particle emission
 +
(C.E.) emission
• Selection rules:
• Fermi:
DT=0 ; DJ=0 ; pf = pi
• Gamow-Teller: DT=0±1; DJ=0±1 ; pf = pi
• Reduced transition probability:
T1 / 2
K
C
ft  f *


2
2 2
2
B.R .
B(F)  B(GT)
G V   GA 
Florence, 13-18 January 2008
M.J.G. Borge, IEM, CSIC, Madrid (Spain)
E, 
Level density
Spin, Isospin
-decay properties
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Nuclear Experimental
Production Methods
Short separation times
(identification of very short T1/2
species)
 Direct determination of B.R.
 High detection efficiency
(implantation of the source)
Simultaneous measurement
of many nuclei
Pure beam
High magnetic resolving
power
Full isotopic chain
Very good beam quality
 Low energy
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 Point like sources
M.J.G. Borge, IEM, CSIC, Madrid (Spain)
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State-of Art p spectrum ( = 4 keV) @ ISOL-Facilities
CSIC
Grupo de Física
Nuclear Experimental
Super-conducting solenoid
B=3.5 Tesla
p-spectrum free
of -summing
0
2
33Ar
Ep (MeV) 3
4
32Ar
Study of the proton line shape
 Physics beyond the SM (Björn’s Talk)
 Isospin mixing in Fermi decays
 Configuration mixing
 Level interferences
 Spin assignment
 Excitation energies
0
Adelberger & García, Hyp. Int 129 (2000) 237
2.5
Ep (MeV)
Florence, 13-18 January 2008
3.5
Bhattacharya & García in preparation
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Grupo de Física
Nuclear Experimental
Development of Targets
Studies possible due to the development of the right target
32Ar
VC-target
CaO-target
Equivalent setup
And beam time
¡ Gain of a factor of
2400 in yield!
Florence, 13-18 January 2008
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Fragmentation Facility /Two solutions
Grupo de Física
Nuclear Experimental
Bhattacharya & García in preparation
32Ar
MSU
JC Thomas et al., Eur Phys J A 21 (2004) 419
Counts
GANIL
Energy (keV)
Strong beta summing
Florence, 13-18 January 2008
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First Measurement of p-p correlation in 2p-radioactivity
MSU
Grupo de Física
Nuclear Experimental
2002
T1/2 and E2p
compatible with
Sequential &
direct decay
PRC76 (2007)
041304R
Miernik, Pfützner et al.
PRL99 (2007) 192501
70 % of the decay
Direct
decay
PRC72 (2005) 054315
Florence, 13-18 January 2008
M.J.G. Borge, IEM, CSIC, Madrid (Spain)
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Nuclear Experimental
Transition from order to Chaos
Middle Z  High Density Narrow States
Fluctuations  Porter Thomas Distribution
Low Z  Narrow States
Direct structure information
Very low Z  Broad States
R-Matrix description: E, 
Florence, 13-18 January 2008
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Nuclear Experimental
Beta delayed particle emitters
Neutron Rich Nuclei
Halo structure
Disappearance
of magic numbers
B.Jonson & K. Riisager, NPA693 (2001) 77
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Nuclear Experimental
The Survival of Magic Numbers
The shell structure and the
associated gaps are different
far from stability.
Number of Protons
Existence/survival of Magic Numbers
depends on
1.
The size of the gap
2.
Structure of mean field near
Fermi level (correlations np-nh
The disappearance of Magic Numbers
was first observed in 31,32Mg.
In N=8, 11Li the gain in correlation is
due to Pairing
New Magic Number
No Magic
In discussion
Number of Neutrons
Florence, 13-18 January 2008
In N=20 and N= 28 the gain in
correlations 2p-2h is due to
cuadrupole interaction.
The play of correlations can be so
subtle that if one adds 2p to
32Mg we have the double magic
nucleus 34Si.
M.J.G. Borge, IEM, CSIC, Madrid (Spain)
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-decay of halo nuclei
 Halo can affect beta decay in different ways; the
spatial extension of the halo state reduces the overlap
with the daughter states.
 Affect one transition or globally the BGT
i.e. in the case of 11Li T1/2 and -B.R.  (P1/2)2 < 50 %
 The halo nucleons decay almost independently from the core,
i.e. decay to the continuum: i. e. d
 Assuming halo state can be factorised
(Nilsson et al, Hyp. Int 129 (2000) 67)
βhalo state> = β(halo> core>) = (βhalo> ) core> + halo>(βcore>)
 Similar decay pattern of the 2n-halo nucleus and its core
Florence, 13-18 January 2008
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Beta decay of an exotic nuclei
Grupo de Física
Nuclear Experimental
3/2-
20.6
11
3
Even a neutron rich- nuclei
emit charged particles
-
Li8
1996
17.916
T1/2 = 8 ms
1983
1966
9Li+d
15.721
9Li
8Li+t
10.59
1980
8.82
1979
7.315
d
8.982
2+3n
9Be+2n
0.320
1974
Energías
(MeV)
0.320
11Be
Florence, 13-18 January 2008
0.504
10Be+n
½-

11Be
½+
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βd- spectrum of 6He
Grupo de Física
Nuclear Experimental
Qd(Z,A) = 3.007 – S2n(MeV);
Anthony et al.,
6He, 8He, 11Li, 14Be, 17B..etc
M.J.G. Borge et al., Nucl. Phys. A560 (1993)
664
+d
6Li
Zhukov et al., PRC47
(1993) 2937
Intensity (decay-1 MeV-1)
6He
-
PRC 65 (2002) 034310
βd-6He
10-4
F.C. Baker, Phys. Lett.
B 322 (1994) 17
10-5
11Li
D. Baye et al.,
Prog. Th. Phys.
91 (1994) 271
10-6
Exploring w.f.  10 fm
00
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Ed (keV)
500
M.J.G. Borge, IEM, CSIC, Madrid (Spain)
1000
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Nuclear Experimental
βd- spectrum of
11Li
• Implantation in a thin, highly segmented
silicon detector
@ TRIUMF
Raabe et al, PRL submitted
• ISOL beams: intense, pure,
good energy definition
 control on the implantation
• Full energy of ions is measured
• High efficiency
• Precise normalisation
• Identification of channels through
implantation-decay-decay correlations
in each pixel
βd-11Li
Zhukov
PRC 52
(95)2461
Baye
PRC79(06)064302
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Polarized radioactive beams: 11Li @ TRIUMF
Grupo de Física
Nuclear Experimental
11Li
3/2
3/2
8.8
8
11Be
7
6.179
5
5.958
2.6 MeV
3.4 MeV
10Be
oSpin polarized 11Li beam
o , n, n coincidences
oSpin and parities of 7 levels in 11Be
assigned.
Florence, 13-18 January 2008
Hirayama, Phys. Lett. B 611 (2005)239
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¿ Similar decay pattern of halo nuclei & core ?
Grupo de Física
Nuclear Experimental
Factorisation holds for the 2n-halo
14Be
and its core
14Be
12Be
< 4 % to bound states
Pn = 101  4 %
Feeding to 1+ > 38 %; logft 3.5-4
P2n + 3P3n = 0.8  = 8 %
Dufour et al., PLB206 (1988) 195
Belbot et al.,PRC56 (1997) 3038
Bergmann et al NPA658 (1999) 129
Can the halo state wave function of
 Study of the decay of
highly excited states
Florence, 13-18 January 2008
11Li
11Li
be factorised?
and 9Li with emphasis in the
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A = 9 isobar
CSIC
Grupo de Física
Nuclear Experimental
≈3
 = δ3.4(7)
5/2-
3/2-
5/2-
13.257
=0.45
(1/2,5/2)-
(1/2)3/2
-
δ=1.2±0.5
54.1(15)%
3/2-
δ ≈= 00.032(3)
Nyman et al., NPA 510 (1990) 189
PLB576 (2003)55
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Mikolas et al., PRC 37 (1988) 766
F. Ajzenberg-Selove, NPA 490 (1988) 1
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NP A692(2001)427
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Charged particle emission in the 11Li-decay
Current knowledge:
?
Four decay channels
Two states in
18.3 MeV.
11Be:
10.6 and
Theory: SM predicts
B(GT) strength distribution
peaks between 15 and 20
MeV. T. Suzuki and T. Otsuka, PRC 56(1997)847
Experiment:  doppler
broadening suggests significant
(6%) feeding of states in this
region. H.O.U. Fynbo et al., NPA736 (2004)39
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11Li
Beam
Analysis techniques
Energy & momentum
conservation
6He++n
60 g/cm2
 

p1  p2  pn  0
Momentum
reconstruction
Excitation energy of
the 1-2 system:

 
 
P1- 2 
p1 p2
•Deadlayer
m1 andmcarbon-foil
2
energy losses corrected
•-background subtraction:
Florence, 13-18 January 2008
Efront- Eback  40 keV
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Nuclear Experimental
Charged Particle Coincidences
127º - 180º
D2
Florence, 13-18 January 2008
M. Langevin et al.,
NPA 366(1981) 449
D4
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Nuclear Experimental
Evidence of decay through the 7He resonance
E11Be
Q1
8.33
7He(gs)
E’
d  10 cm
2005
127º - 180º
2007
d  8.5 cm
E 11 Be  E '
m 11 Be
m'
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Q2
7.91
6He++n
Contribution of a new
decay channel .
Contribution of a state at
16.3 MeV ( 1 MeV) ). In
agreement with theoretical
expectations and previous
-experiment
E1
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Universal set-up for spectroscopy studies
Grupo de Física
Nuclear Experimental
Set up:
Cube of DSSSD
7 x BC501
Liquid scintillator
15 cm x 30 cm
4-6 Segmented HPGe
Ge
1.2m
TAS
Good scheme for Neutron
detection
2m

3m
Gamma
detection
Fast Scintillators for T1/2
• 3 Glover (4xHPGe)
Neutron Detection
Need to be improved!!
Florence, 13-18 January 2008
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Outlook @ EURISOL
Shell structure @ drip lines
 Changes in the (effective) interaction
Proton drip line and N=Z nuclei
•Spectroscopy beyond the
 New “islands” of inversion
drip line
•Proton-neutron pairing
•Isospin Symmetry
•Isospin Mixing
•GT and Fermi -decays
• Order to chaos
•p / ratios
Production of new isotopes
 New s.p. energies at large N/Z
 T1/2 and Pn-values of new isotopes
Florence, 13-18 January 2008
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12C
from the -decays of 12N and
0+, 1+, 2+ levels selected
15.11
1+
12.71
1+
10.3
7.285
7.6542
4.4389
12B
1+
Florence, 13-18 January 2008
0
Decay
mechanism
12B
?
0,2+Spin ?
0+
2+
0+
M.J.G. Borge, IEM, CSIC, Madrid (Spain)
+
12N
1+
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IGISOL
12C/11B
CSIC
12N/12B+X
Grupo de Física
Nuclear Experimental
p/d
Magnet
12N/12B
 
All 3  events
0+, 2+
1+
3’s, Channel
8Be(0+) excluded
Fynbo et al., PRL 91 (2003) 82502
Fynbo et al., NPA738 (2004) 59
Diget et al, NPA760 (2005) 3
Florence, 13-18 January 2008
Fynbo et al., Nature 433 (2005) 136
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Charged Particle Identification: monolithic Si telescope
Grupo de Física
Nuclear Experimental
DE
E
To distinguish low
energy charged
256 detector
elements á 9 mm2
6
particle: p, d, 32
t, ,
He channels
readout
64 telescopes á 7 mm2
128 readout channels multiplexed
to 1 ADC.
DE stage
1 µm
E stage 400 ± 15 µm
Florence, 13-18 January 2008
64 ch: PA + TFA + CFD +
A + trigger
The Solid Angle is 20% of the DSSSD
but needs 4 times more electronic-channels!
M.J.G. Borge, IEM, CSIC, Madrid (Spain)
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Nuclear Experimental
Determination of beta half-lives in complex background conditions
only pause
Produced
Implanted
Monte Carlo Simulations
 The time sequence of fragment implantation and β
detection are simulated according to the experimental
conditions leaving two free parameters: the lifetimes and
the efficiency
 The code produces time-correlation spectra in forwardand backward-time direction.
 Half-life determination of several new 194-196Re, 199,200Os
and
199,202Ir
isotopes relevant for the r-process.
 With some modifications the method can be used for
continuous beams. T. Kurtukian et al, NIM, submmitted.
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Mirror Asymmetry & Systematics
+ : p → n + e+ + 
- : n → p + e - + 
E.C. : p + e- → n + 
ft+
ftn
p
n
 Allowed Gamow-Teller transitions

ft
ft
-
-1
 = nuc + SCC
p
Thomas et al., AIP Conf. Proc 681, p. 235
 = 4.8 (4) %
(log(ft)<6)
17 couples of nuclei
46 mirror transitions
Average asymmetry  :
11 (1) % in the 1p shell (A<17)
0 (1) % in the (2s,1d) shell (17<A<40)
Florence, 13-18 January 2008
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Beta feeding to the 11-12 MeV region in 9Be
Fit of the high energy peak gating on
the 5He(3/2-) channel
11.81 MeV state  91±10%
11.28 MeV state  9 %
(e,p)-scattering on 9Be assumed J = 7/2
Only the participation of the
11.81 MeV state in 9Be
for the beta feeding is considered
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-decay of
11Li
3/2-
20.4
11Li
Q=20.4 MeV
T1/2=8.5 ms

11Be
17.9
&n
10Be+n
0.50 MeV
1974
97%
9Be+2n
7.31 MeV
1979
6He++n
7.90 MeV
2+3n
8.98 MeV
Charged
particles
(and n)
3%
Charged
particles
0.3%
8Li+t
9Li+d
15.72 MeV
17.91 MeV
15.7
8Li+t
8.9
n
1980
7.9
n
3/2-
7.3
9Be

1983
1/2-
0
 1/2+
0.5
11Be
Florence, 13-18 January 2008
2+3n
6He++n
1980
1996
9Li+d
M.J.G. Borge, IEM, CSIC, Madrid (Spain)
0+
10Be
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11Li,
Grupo de Física
Nuclear Experimental
320 keV
gamma rays
½-

11Be
½+
M.J.G. Borge et al., PRC55 (97) R8
N. Aoi et al., NPA616 (97) 181c
D. Morrisey et al., NPA627 (97) 222
Q = 20.62 MeV, T 1/2= 8.2 ms
b(320) = 6.3(6) %
log ft = 5.73
(1s1/2)2/(0p1/2)2 ~1
Florence, 13-18 January 2008
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Nuclear Experimental
Exotic Radioactivities
1p-radioactivity
(Z,N)  p + (Z-1,N)
2p-radioactivity
(Z,N)  2p + (Z-2,N)
Zn
Ni
Fe
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Nuclear Experimental
Tanihata,
1985
Halo nuclei
Energy threshold
effect
Highlight by nuclear
reactions
6Li
7Li
8Li
9Li
11Li
Florence, 13-18 January 2008
Effects in beta
decay
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