Structure of the heavy Ca isotopes and effective interaction in the - PowerPoint PPT Presentation

Structure of the heavy Ca isotopes and effective interaction in the sd-fp shell F. Maréchal Institut de Recherches Subatomiques, Strasbourg (France) Physics and Motivations Experiment and Results Conclusions and Perspectives

Heavy calcium isotopes Z=20 closed shell for protons N very simple wave functions 28 40 Z 2p 3/2 2p 1/2 1f 5/2 Isotopes approaching the dripline Ni Ni 28 nuclei close to limit of existence information on strucutre of Z>20 1f 7/2 r process Astrophysical interest r process Ti Sc 20 Ca Nuclear structure K test of the effective interaction 2s, 1d n-n interaction in the fp shell A = 53 n-p interaction across the sd-fp shell neutron dripline (Möller & Nix, 1995) better description of heavier nuclei r process (O. Sorlin, K.L. Kratz, priv. com.) such as neutron-rich nickel isotopes

Effective interaction between orbitals f 5/2 p 1/2 fp shell p 3/2 Z=28 N=28 Evidence for a strong attractive interaction f 7/2 between proton and neutron spin-orbit partners Z=20 N=20 d 3/2 π j > (j=l+1/2) and ν j < (j=l-1/2) s 1/2 sd shell Otsuka et al., Phys. Rev. Lett. 82, 082502 (2001) d 5/2 Z=8 N=8 16 O core π ν typical case: N=29 isotones in fp shell 57 Ni ( π f 7/2 full) and 49 Ca ( π f 7/2 empty) E x (MeV) same behavior for N=16 isotones in sd shell: effective single particle energy of d 3/2 orbital 5/2- 4 much higher in 24 O ( π d 5/2 empty) than in 30 Si ( π d 5/2 full) 1/2- 2 1/2- mapping out the shell structure of nuclei can mapping out the shell structure of nuclei can mapping out the shell structure of nuclei can 5/2- bring information on the nucleon-nucleon bring information on the nucleon-nucleon bring information on the nucleon-nucleon 3/2- 3/2- 0 interaction matrix elements interaction matrix elements interaction matrix elements 57 Ni 29 49 Ca 29 28 20

Neutron number 20 22 24 26 28 30 32 Ca K Ar Cl S Shell Model Calculations P need single-particle energies Si and 2-body interactions Al key nuclei: (closed shell ± 1) ⊗ (closed shell) Mg 39 K (N=20 closed shell): single-particle energies in sd shell 41 Ca (Z=20 closed shell): single-particle energies in fp shell 35 Si and 47 K to help to fix the 2-body monopole interactions in the region

Ca isotopic lower part of fp shell relatively well known (spectroscopy of 39-47 K and 35 Si) chain How to get information on the upper part (f 5/2 orbital behavior) ? 2+ excited state in 54 Ca� ( ν p 1/2 ) 1 ⊗ ( ν f 5/2 ) 1 n-n interaction monopole terms 4+ excited state in 52 Ca� ( ν p 3/2 ) 3 ⊗ ( ν f 5/2 ) 1 6 6 Excitation Energy (MeV) Excitation Energy (MeV) 2+ KB3 KB3G 4+ 5 5 2+ 4+ 4 4 3 3 2 2 1 1 0 0 22 24 26 28 30 32 34 22 24 26 28 30 32 34 Neutron number Neutron number F. Nowacki and E. Caurier (Priv. Comm.) discrimination between interactions

β decay of neutron-rich nuclei S β large Q β -S n energy window GTR high P 1n and P 2n values competition between γ and neutron emission IAS need for efficient γ and neutron detection for β - γ , β -n and β -n- γ A Z coincidence measurements 2n β - A-2 (Z+1) 1n Q β A-1 (Z+1) S 2n direct knowledge of Q β , T 1/2 , I β , P x n and E x S n J π values and GT strength A (Z+1) distribution in Q β window P.G. Hansen and B. Jonson

RADIOACTIVE LABORATORY 1-1.4 GeV PROTONS ROBOT GPS CONTROL HRS ROOM REX-ISOLDE ( 2.3 MeV/A ) IS392 Experiment EXPERIMENTAL HALL ( 60 KeV )

UC 2 -C target (53 g/cm 2 ) Production: Yields (at/pulse) Experimental W surface ionization source 49 K ~ 1.5 10 6 HRS mass separator Setup 50 K ~ 8.0 10 4 (M/ ∆ M ~ 8000) 51 K ~ 1.2 10 4 52 K ~ 2.5 10 2 LA1 beamline 53 K ~ 1.0 10 1 transmission ~ 90 % TONNERRE array (x16) (LPC Caen - IFIN Bucharest) Low energy neutron detectors (x8) (IReS Strasbourg) En: 0.2-7 MeV En: 0.05-4 MeV ε ~ 11% at 1 MeV ε ~ 0.5% at 1 MeV Beam 4 π β counter (IReS Strasbourg) Ge Clusters (x2) start n-TOF (MINIBALL Collaboration) ε ~ 70% ε ~ 5% at 1.3 MeV

52 K decay: preliminary results (0-,2-) P 1n =67(10) % T 1/2 = 105(5) ms, P n =107(20) % 52 116(6) ms K Langevin et al., Phys. Lett. 130B, 251 (1983) P 2n =8(3) % 19 2+ state and 2563 keV transition in 52 Ca ~ 8 % Huck et al., Phys. Rev. C 31, 2226 (1985) Q β = 16310 (840) keV ~ 0.5 % ~ 7 . 5 2+ % ~ 20 % 1026 4493 0+ S 2n S n 9080 4390 50 3500 13.9(6) s Ca 3460 20 2934 log (f 1 t) I β (%) ~ 47 % 2378 1718 7.8(3) 1.9(1) 5950 (3/2-) S n 4690 51 10.0(8) s Ca 8.2(3) 2.8(3) 3990 20 2+ 7.7(2) 20.3(5) 2563 new T 1/2 , P 1n and P 2n values 3 new transitions in 52 Ca 7 new transitions in 51 Ca 0+ 1 new transition in 50 Ca < 4.0 52 1 transition (3150 keV) not attributed 4.6(3) s Ca 20

53 K decay: preliminary results (1/2+,3/2+) T 1/2 = 30(5) ms, P n =100(30) % 53 30(5) ms K Langevin et al., Phys. Lett. 130B, 251 (1983) 19 S 2n S n 8150 4690 Q β = 15900 (860) keV 2+ 2563 0+ S n 3460 52 4.6(3) s Ca (3/2-,5/2-) 2220 20 1 new transition in 53 Ca: 2220 keV (1/2-) 1 new transition in 52 Ca: 2563 keV 53 1 transition (3150 keV) not attributed 90(15) ms Ca 20

N=32 subshell closure reproduced 52 Ca by KB3 and KB3G interactions ν p 3/2 - ν p 1/2 gap relatively well known 1+ 5.95 5.77 J π of the 3.99 MeV state ? 4+ 2+ 5.49 5.44 natural parity state: info on f 5/2 0+ 0+ 1+ 4.43 4.28 4+ only if 52 K g.s. has J π =2- (0+,1+,4+) 4.23 4+2+ 3.99 3.94 3.90 2+ possible with same 1+ ( ν p 3/2 ) 3 ⊗ ( ν f 5/2 ) 1 configuration 3.24 1+ 3.08 but no E 2 transition to g.s. 2+ 2+ 2+ 2.56 2.43 2.35 first 2+ (p 3/2 ⊗ p 1/2 ) rules out a possible 1+ (p 3/2 ⊗ p 1/2 ) non-natural parity state ? 0+ 0+ 0+ GT strength function calculation 0.00 0.00 0.00 could assign the J π of the 3.99 MeV state KB3 Exp. KB3G strength must fit the feeding I β ~2%

Comparison Exp. vs. Theory for odd Ca isotopes 49 Ca: good agreement between 5/2- 4.07 experiment and theory (3/2-,5/2-) 3.50 3.59 5/2- (3/2-,5/2-) 2.93 lower part of fp shell well known (5/2-) (3/2-) 2.38 2.22 1/2- 2.02 (1/2-) 1.72 Exp. 51 Ca: preliminary results (1/2-) 3/2- 0.00 3/2- 0.00 0.00 good agreement for lowest states 49 51 53 Ca Ca Ca J π assignment depends on interaction above 2.5 MeV 5/2- 3.84 5/2- 3.80 3.79 5/2- 2.79 53 Ca: 3/2- 5/2- 2.28 2.16 KB3 1/2- 1.81 1/2- 1.57 β decay of the N=33 55 Ti nucleus (~GXPF1) consistent with a 5/2- g.s. 0.00 0.00 0.00 3/2- 3/2- 1/2- Mantica et al., Phys. Rev. C 68,044311 (2003) 49 51 53 Ca Ca Ca p 1/2 and f 5/2 orbitals very close 5/2- 5/2- state too high with KB3 3.89 3.44 5/2- 2.22 MeV state: J π =3/2- 5/2- 2.82 5/2- 3/2- 2.12 2.16 KB3G 1/2- better overlap with 53 K g.s. 1.82 1/2- 1.61 5/2- 1.03 configuration 1/2 + or 3/2 + 0.00 0.00 0.00 3/2- 3/2- 1/2- Results support KB3G with 49 51 53 Ca Ca Ca a more attractive p 3/2 -f 5/2

Conclusions we have measured the decays of 52 K, 52 K and 52 K at CERN using efficient n and γ detection decay of 52 K: new T 1/2 , P 1n and P 2n values for 52 K 11 new transitions identified new neutron transitions observed ~10 new n- γ coincidences (mainly to 1.72 and 2.38 MeV states) 2 new low energy neutron transitions to 51 Ca g.s. decay of 53 K: 3 new transitions identified new neutron transitions observed but statistics very low Perspectives refine neutron spectroscopy for 52 K decay (E x , feedings) experimental data: analysis of 53 K experiment (july 03) to complete decay scheme (n, γ ) calculations: GT strength calculation to locate non-natural parity states tuning of n-n interaction in fp shell: evolution of p 1/2 -f 5/2 orbitals tuning of p-n interaction in sd-fp shell: systematic of negative parity states look for possible developments of target and ion source to study 54 K� 54 Ca

Many thanks to all my colleagues from Geneva, Bucharest, Caen, Constantine and Strasbourg who have made this work possible F. Perrot J.C. Angélique G. Ban P. Baumann F. Benrachi C. Borcea J.C. Caspar A. Buta E. Caurier S. Courtin P. Dessagne D. Etasse C. Jollet S. Grévy G. Heitz F.R. Lecolley E. Liénard G. Le Scornet C. Miehé F. Negoita F. Nowacki N. Orr E. Poirier M. Ramdhane I. Stefan the IReS (Strasbourg) workshop and the ISOLDE collaboration.