Structure and Reactions of Exotic Nuclei, 2426 February 2005

1
N? 3n light nuclei via the (7Li,7Be) reaction
Francesco Cappuzzello
Structure and Reactions of Exotic Nuclei, 24-26
February 2005
2
What exactly?
Hard core
An important part of the phase space is
represented by

• BSEC
• (Bound States Embedded
• in the Continuum)

• N 1 7He
• N 2 11Be
• N 3 15C
• N 4 19O
• N 5 23Ne
• N 6 27Mg

DCP (Dynamical Core Polarization)
Systematic study via the (7Li,7Be) reaction
3
(7Li,7Be) reaction over 7Li, 11B, 15N, 19F, 23Na,
27Al

• Study of single particle isovector excitations
• Problem of the core polarisation
• Systematic study of the (7Li,7Be) reaction at low
  incident energy as function of charge asymmetry
  and mass

References F.Cappuzzello et al., Excited states
of 11Be, Phys.Lett B516 (2001) 21 F.Cappuzzello
et al., Analysis of the 11B(7Li,7Be)11Be reaction
at 57 MeV in a Microscopic Approach, Nucl. Phys.
A739 (2004) 30. F.Cappuzzello et al., Excited
states of 15C, EuroPhys.Lett. 65 (2004) 766
C.Nociforo et al. Investigation of light
neutron-rich nuclei via the (7Li,7Be) reaction,
Acta Physica Polonica, B34 (2003) 2387. S.E.A.
Orrigo et al. On the line shape of 15C submitted
to Phis. Lett. B 2004
4
Examples
7Be detected with the IPN-Orsay Split Pole
Counts
DCP regime
Single particle regime
?l 9?, 14 keV/ch.
11B(7Li,7Be)11Be at 57 MeV
11Be excitation energy (MeV)
Counts
Single particle regime
?l 14?, 55 keV/ch.
15N(7Li,7Be)15C at 55 MeV
DCP regime
15C excitation energy (MeV)
5
7 He and 19O spectra via (7Li,7Be) at 56 MeV
19F(7Li,7Be)19O
Target LiFC ?riv 0
6
Results of microscopic QRPA calculations
The strength is well reproduced for single
particle transitions, namely ½ gs, ½- excited
state at 0.32 MeV and 5/2 state at 1.77 MeV
Single particle
The observed fragmentation beyond 2 MeV is not
reproduced
7
Results of microscopic DWBA calculations
11Be1.77
Direct one step mechanism
No scaling factors
Angular distributions reproduced without any
scaling factor or parameter tuning
11BeGS
No scaling factors
8
Nuclear structure model
Quasiparticle-core coupling model (QPC) (Bohr
Mottelson)
eff. Hamiltonian of the odd-mass system
Odd-mass system w. f.
Quasiparticle-RPA approach
3qp
s.p. mixing 1qp
V13 couples
where is the g.s. correlated of the
even-mass core and
by Bogolyubov-Valatin transformation
state-dependent mass operator
with
H. Lenske, Progr. in Part. and Nucl. Phys.
A693(2001)616
9
15C response function
s1/2 and d5/2 strength functions of 15C
calculated with Jc?3

g.s. configuration
0.110 MeV
excited configuration dominance of core
excitations (1-,2,3-)
Strong fragmentation of the strength for
9ltExlt15 MeV
C. Nociforo, H.Lenske, in preparation
10
Some experimental consideration
Experiments need high energy resolution
(?1/1000), forward angles (around 0?) exploration
and large momentum byte (10?20)
Magnetic spectrographs
IPN-Orsay Split-Pole
Energy resolution ? 1/1000 Momentum byte ? 36
Solid angle ? 1.8 msr
The small solid angle limits the possibility to
study weak narrow states above neutron emission
threshold
11
The MAGNEX opportunity
Large solid angle and high energy resolution
A.Cunsolo et al., NIMA 481 (2002) 48 A.Cunsolo et
al., NIMA 484 (2002) 56 A.Cunsolo et al., NIMA
495 (2002) 216
12
Conclusions and outlooks

• Exploration of excited states of light neutron
  rich nuclei is a rich source of information about
  nuclear structure
• High energy resolution is crucial to that
  purpose
• Use of refined microscopic theories is also
  fundamental
• Challanges
• Use of the MAGNEX spectrometer (starting from
  next weeks)
• Full development of the microscopic DCP theory
  (on the run)

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The Charge Exchange collaboration
 A.Cunsolo, F.C., A.Foti, A.Khouaja,
C.Nociforo, S.E.A.Orrigo, J.S.Winfield,
M.Cavallaro  INFN-LNS, Catania, Italy INFN,
Sez. Catania, Catania, Italy Dipartimento di
Fisica, Università di Catania, Catania, Italy D.
Beaumel, S. Fortier, Institut de Physique
Nucléaire, IN2P3-CNRS, Orsay, France
H.Lenske Universitatat Giessen, Giessen,
Germany
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15N(7Li,7Be)15C reaction at 55 MeV
Counts
single particle regime
? 14? (55 keV/ch)
DCP regime
15C excitation energy (MeV)
F. Cappuzzello et al., Phys. Lett. B516, 21
(2001) C. Nociforo et al., Acta Phys. Polonica
B34 ,2387 (2003) F. Cappuzzello et al., Europhys.
Lett. 65, 766 (2004) F. Cappuzzello et al., Nucl.
Phys. A739, 30 (2004)
15
15C and 11Be spectra via (7Li,7Be) at 57 MeV
qlab10 136 keV/ch
0.74
counts
8.5
10.3
g.s.
15C Excitation Energy (MeV)
100 80 60 40 20 0
6.0
15C state at 8.49 MeV (FWHM 27050 keV)
qlab9 140 keV/ch
counts
9.5
11Be state at 6.05 MeV (FWHM 32040 keV)
0 2 4
6 8 10 12
14 16
11Be Excitation Energy (MeV)
F.Cappuzzello et al., Phys.Lett.B516(2001)21
16
Core excitations
For large A/Z (
A-1 ) core soft
Apparence of low energy (vibrational) states ( 2
, 3- )
Evidence of 2 core excitation in 11Beg.s.
1H(11Be,10Be) at 35.3 MeV/u
2
J.S.Winfield et al., Nucl.Phys. A683(2001)48
17

• CEX-QRPA

Bogoliubov-Valatin transformation
From HFB calculations
Projection over isospin t subspace
Average treatment of the configurations ortogonal
to 2QP ones (i.e. 4QP...)
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• CEX-QRPA
• (Charge EXchange Quasi-particle Random Phase
  Approximation)

Need to describe effect due to the proximity of
the continuum

• Green function approach to QRPA

F.T.Baker et al. Phys. Rep. 289, 235 (1997)
Response function
Dyson Equation