Structure and Reactions of Exotic Nuclei, February 2005 Francesco Cappuzzello N*  + 3n light nuclei via the ( 7 Li, 7 Be) reaction

N = 1 7 He N = 2 11 Be N = 3 15 C N = 4 19 O N = 5 23 Ne N = 6 27 Mg … BSEC (Bound States Embedded in the Continuum) DCP (Dynamical Core Polarization)Core Polarization Systematic study via the ( 7 Li, 7 Be) reaction What exactly? Hard core Softer core An important part of the phase space is represented by

( 7 Li, 7 Be) reaction over 7 Li, 11 B, 15 N, 19 F, 23 Na, 27 Al Study of single particle isovector excitations Problem of the core polarisation Systematic study of the ( 7 Li, 7 Be) reaction at low incident energy as function of charge asymmetry and mass References: F.Cappuzzello et al., Excited states of 11 Be, Phys.Lett B516 (2001) 21 F.Cappuzzello et al., Analysis of the 11 B( 7 Li, 7 Be) 11 Be reaction at 57 MeV in a Microscopic Approach, Nucl. Phys. A739 (2004) 30. F.Cappuzzello et al., Excited states of 15 C, EuroPhys.Lett. 65 (2004) 766 C.Nociforo et al. Investigation of light neutron-rich nuclei via the ( 7 Li, 7 Be) reaction, Acta Physica Polonica, B34 (2003) S.E.A. Orrigo et al. On the line shape of 15 C submitted to Phis. Lett. B 2004

Examples: 11 B( 7 Li, 7 Be) 11 Be at 57 MeV 15 N( 7 Li, 7 Be) 15 C at 55 MeV Counts  l = 14 , 55 keV/ch.  l = 9 , 14 keV/ch. 15 C excitation energy (MeV) Single particle regime DCP regime 7 Be detected with the IPN-Orsay Split Pole Counts 11 Be excitation energy (MeV)

Target LiF+C  riv = 0° 7 He and 19 O spectra via ( 7 Li, 7 Be) at 56 MeV 19 F( 7 Li, 7 Be) 19 O

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 The observed fragmentation beyond 2 MeV is not reproduced Single particle

Results of microscopic DWBA calculations 11 Be GS 11 Be* 1.77 No scaling factors Angular distributions reproduced without any scaling factor or parameter tuning Direct one step mechanism

Nuclear structure model Quasiparticle-RPA approach: eff. Hamiltonian of the odd-mass system by Bogolyubov-Valatin transformation 3qp where is the g.s. correlated of the even-mass core and with s.p. mixing 1qp Quasiparticle-core coupling model (QPC) (Bohr & Mottelson) V 13 couples state-dependent mass operator Odd-mass system w. f. : H. Lenske, Progr. in Part. and Nucl. Phys. A693(2001)616

15 C response function s 1/2 and d 5/2 strength functions of 15 C calculated with J c  3 Strong fragmentation of the strength for 9<E x <15 MeV g.s. configuration: MeV [ C. Nociforo, H.Lenske, in preparation excited configuration: dominance of core excitations (1 -,2 +,3 - )

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

The MAGNEX opportunity Maximum magnetic rigidity1.8 T m Solid angle 51 msr E max /E min 1.5 Total energy resolution (target 1 mm 2 ) (90% of full acceptance)  1000 Mass resolution 250 A.Cunsolo et al., NIMA 481 (2002) 48 A.Cunsolo et al., NIMA 484 (2002) 56 A.Cunsolo et al., NIMA 495 (2002) 216 Large solid angle and high energy resolution

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 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

15 N( 7 Li, 7 Be) 15 C reaction at 55 MeV 15 C excitation energy (MeV)  = 14  (55 keV/ch) DCP regime single particle regime Counts 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)

g.s C Excitation Energy (MeV) counts  lab =10° 136 keV/ch  lab =9° 140 keV/ch 11 Be Excitation Energy (MeV) C and 11 Be spectra via ( 7 Li, 7 Be) at 57 MeV 11 Be state at 6.05 MeV (FWHM 320±40 keV) F.Cappuzzello et al., Phys.Lett.B516(2001)21 counts C state at 8.49 MeV (FWHM 270±50 keV)

Core excitations For large A/Z ( A-1 ) core soft Evidence of 2 + core excitation in 11 Be g.s. 1 H( 11 Be, 10 Be) at 35.3 MeV/u J.S.Winfield et al., Nucl.Phys. A683(2001) Apparence of low energy (vibrational) states ( 2 +, 3 - )

CEX transitions 19 F gs 19 O  CEX- QRPA Projection over isospin τ + subspace Average treatment of the configurations ortogonal to 2QP ones (i.e. 4QP...) Bogoliubov-Valatin transformation From HFB calculations

Green function approach to QRPA Dyson Equation CEX-QRPA (Charge EXchange Quasi-particle Random Phase Approximation) F.T.Baker et al. Phys. Rep. 289, 235 (1997) Response function Need to describe effect due to the proximity of the continuum