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Structure and Reactions of Exotic Nuclei, 24-26 February 2005 PowerPoint PPT Presentation


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N*  + 3n light nuclei via the ( 7 Li, 7 Be) reaction. Francesco Cappuzzello. Structure and Reactions of Exotic Nuclei, 24-26 February 2005. N = 1 7 He N = 2 11 Be N = 3 15 C N = 4 19 O N = 5 23 Ne

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Structure and Reactions of Exotic Nuclei, 24-26 February 2005

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Structure and reactions of exotic nuclei 24 26 february 2005

N* + 3n light nuclei via the (7Li,7Be) reaction

Francesco Cappuzzello

Structure and Reactions of Exotic Nuclei, 24-26 February 2005


Structure and reactions of exotic nuclei 24 26 february 2005

N = 1 7He

N = 2 11Be

N = 3 15C

N = 4 19O

N = 5 23Ne

N = 6 27Mg

BSEC

(Bound States Embedded

in the Continuum)

Softer core

What exactly?

Hard core

An important part of the phase space is represented by

DCP

(Dynamical Core Polarization)

Systematic study via the (7Li,7Be) reaction


7 li 7 be reaction over 7 li 11 b 15 n 19 f 23 na 27 al

(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 15Csubmitted to Phis. Lett. B 2004


Examples

7Be detected with the IPN-Orsay Split Pole

Examples:

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)


7 he and 1 9 o spectra via 7 li 7 be at 5 6 mev

7 He and19O spectra via (7Li,7Be)at 56 MeV

19F(7Li,7Be)19O

Target LiF+C

riv = 0°


Structure and reactions of exotic nuclei 24 26 february 2005

Results of microscopic QRPA calculations

Single particle

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

The observed fragmentation beyond 2 MeV is not reproduced


Structure and reactions of exotic nuclei 24 26 february 2005

Results of microscopic DWBA calculations

11Be*1.77

Direct one step mechanism

No scaling factors

Angular distributions reproduced withoutany scaling factor or parameter tuning

11BeGS

No scaling factors


Nuclear structure model

Nuclear structure model

Quasiparticle-core coupling model (QPC)(Bohr & Mottelson)

eff. Hamiltonian of the odd-masssystem

Odd-mass system w. f. :

Quasiparticle-RPA approach:

s.p. mixing1qp

3qp

V13couples

where is the g.s. correlated of the even-mass coreand

byBogolyubov-Valatin transformation

state-dependent mass operator

with

H. Lenske, Progr.in Part. and Nucl.Phys. A693(2001)616


15 c response function

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 9<Ex<15 MeV

C. Nociforo, H.Lenske, in preparation


Structure and reactions of exotic nuclei 24 26 february 2005

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


Structure and reactions of exotic nuclei 24 26 february 2005

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


Structure and reactions of exotic nuclei 24 26 february 2005

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)


The charge exchange collaboration

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


Structure and reactions of exotic nuclei 24 26 february 2005

15N(7Li,7Be)15C reaction at 55 MeV

Counts

single particleregime

= 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 c and 11 be spectra via 7 li 7 be at 57 mev

15C and 11Be spectra via (7Li,7Be) at 57 MeV

qlab=10° 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 270±50 keV)

qlab=9° 140 keV/ch

counts

9.5

11Be state at

6.05 MeV

(FWHM 320±40 keV)

0 2 4 6 8 10 12 14 16

11Be Excitation Energy (MeV)

F.Cappuzzello et al., Phys.Lett.B516(2001)21


Core excitations

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


Structure and reactions of exotic nuclei 24 26 february 2005

CEXtransitions19Fgs 19O

  • CEX-QRPA

Bogoliubov-Valatin transformation

From HFB calculations

Projection over isospin τ+ subspace

Average treatment of the configurations ortogonal to 2QP ones (i.e. 4QP...)


Structure and reactions of exotic nuclei 24 26 february 2005

CEX-QRPA

(Charge EXchange Quasi-particle Random Phase Approximation)

Green function approach to QRPA

Need to describe effect due to the proximity of the continuum

F.T.Baker et al. Phys. Rep. 289, 235 (1997)

Response function

Dyson Equation


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