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 Isotopes approaching the dripline Nuclear structure Astrophysical interest r process closed shell for protons very simple wave functions nuclei close to limit of existence information on strucutre of Z>20 test of the effective interaction n-n interaction in the fp shell n-p interaction across the sd-fp shell better description of heavier nuclei such as neutron-rich nickel isotopes

Ni Ni

A = 53

Sc Ti

1f7/2

r process

N Z

neutron dripline (Möller & Nix, 1995) r process (O. Sorlin, K.L. Kratz, priv. com.)

Ca K

2p3/2 1f5/2 2p1/2 2s, 1d

28 20 28 40

d5/2 s1/2 d3/2 f7/2 p3/2 p1/2 f5/2 Z=28 Z=20 N=28 N=20 Z=8 N=8 fp shell sd shell

ν π

16O core

Otsuka et al., Phys. Rev. Lett. 82, 082502 (2001)

Evidence for a strong attractive interaction between proton and neutron spin-orbit partners πj> (j=l+1/2) and νj< (j=l-1/2)

57Ni (πf7/2 full) and 49Ca (πf7/2 empty)

same behavior for N=16 isotones in sd shell: effective single particle energy of d3/2 orbital much higher in 24O (πd5/2 empty) than in

30Si (πd5/2 full)

Ex (MeV) 2 4

57Ni29 28 49Ca29 20

5/2- 5/2- 1/2- 1/2- 3/2- 3/2-

typical case: N=29 isotones in fp shell mapping out the shell structure of nuclei can bring information on the nucleon-nucleon interaction matrix elements mapping out the shell structure of nuclei can bring information on the nucleon-nucleon interaction matrix elements mapping out the shell structure of nuclei can bring information on the nucleon-nucleon interaction matrix elements

Effective interaction between orbitals

Ca K Ar Cl S P Si 20 22 24 26 28 30 32 Al Mg

need single-particle energies and 2-body interactions

key nuclei: (closed shell ± 1)⊗(closed shell)

39K (N=20 closed shell): single-particle energies in sd shell 41Ca (Z=20 closed shell): single-particle energies in fp shell 35Si and 47K to help to fix the 2-body monopole interactions in the region

Shell Model Calculations

Neutron number

22 24 26 28 30 32 34 1 2 3 4 5 6

Excitation Energy (MeV) KB3G Neutron number

2+ 4+ 2+ 4+ 22 24 26 28 30 32 34 1 2 3 4 5 6

Excitation Energy (MeV) KB3 Neutron number

discrimination between interactions

How to get information on the upper part (f5/2 orbital behavior) ? lower part of fp shell relatively well known (spectroscopy of 39-47K and 35Si) n-n interaction monopole terms 2+ excited state in 54Ca (νp1/2)1⊗(νf5/2)1 4+ excited state in 52Ca (νp3/2)3⊗(νf5/2)1

Ca isotopic chain

• F. Nowacki and E. Caurier (Priv. Comm.)

β decay of neutron-rich nuclei

large Qβ-Sn energy window high P1n and P2n values

competition between γ and neutron emission

need for efficient γ and neutron detection for β-γ, β-n and β-n-γ coincidence measurements direct knowledge of Qβ, T1/2, Iβ, Pxn and Ex Jπ values and GT strength distribution in Qβ window

IAS GTR 2n 1n

A-2(Z+1) AZ A-1(Z+1) A(Z+1)

Sβ Qβ Sn S2n β- P.G. Hansen and B. Jonson

ROBOT RADIOACTIVE LABORATORY

GPS HRS

REX-ISOLDE

( 2.3 MeV/A )

CONTROL ROOM 1-1.4 GeV PROTONS EXPERIMENTAL HALL

( 60 KeV )

IS392 Experiment

Beam Ge Clusters (x2) ε ~ 5% at 1.3 MeV 4π β counter ε ~ 70% start n-TOF TONNERRE array (x16) ε ~ 11% at 1 MeV En: 0.2-7 MeV Low energy neutron detectors (x8) ε ~ 0.5% at 1 MeV En: 0.05-4 MeV

Experimental Setup

49K ~ 1.5 106 50K ~ 8.0 104 51K ~ 1.2 104 52K ~ 2.5 102 53K ~ 1.0 101

Yields (at/pulse)

Production: UC2-C target (53 g/cm2) W surface ionization source HRS mass separator (M/∆M ~ 8000) LA1 beamline transmission ~ 90 %

(LPC Caen - IFIN Bucharest) (IReS Strasbourg) (MINIBALL Collaboration) (IReS Strasbourg)

Ca

52 20

K

52 19

Ca

51 20

Ca

50 20

1026 1718 2378 2934 3460 3500 4493 4390 2563 3990 4690 5950 9080

52K decay: preliminary results

Sn Sn S2n P2n=8(3) % P1n=67(10) %

(0-,2-) 0+ 2+ 0+ 2+ (3/2-) 4.6(3) s 10.0(8) s 13.9(6) s

~ 8 % ~ 0.5 % ~ 7 . 5 % ~ 20 % ~ 47 %

116(6) ms 1.9(1) 2.8(3) 20.3(5) < 4.0 7.8(3) 8.2(3) 7.7(2) log (f1t) Iβ (%) Qβ = 16310 (840) keV 3 new transitions in 52Ca 7 new transitions in 51Ca 1 new transition in 50Ca 1 transition (3150 keV) not attributed new T1/2, P1n and P2n values

Langevin et al., Phys. Lett. 130B, 251 (1983) Huck et al., Phys. Rev. C 31, 2226 (1985)

T1/2 = 105(5) ms, Pn=107(20) % 2+ state and 2563 keV transition in 52Ca

Ca

53 20

K

53 19

Ca

52 20

2563 4690 2220 3460 8150

53K decay: preliminary results

Sn Sn S2n

(1/2+,3/2+) 0+ 2+ (1/2-) (3/2-,5/2-) 90(15) ms 4.6(3) s 30(5) ms Qβ = 15900 (860) keV 1 new transition in 53Ca: 2220 keV 1 new transition in 52Ca: 2563 keV 1 transition (3150 keV) not attributed

Langevin et al., Phys. Lett. 130B, 251 (1983)

T1/2 = 30(5) ms, Pn=100(30) %

0.00 2.56 3.99 5.95 0.00 2.35 3.08 3.90 3.94 4.23 4.28 0.00 2.43 3.24 4.43 5.44 5.49 5.77 1+ 4+ 2+ 4+2+ 0+ 1+ 0+ (0+,1+,4+) 1+ 1+ 2+ 2+ 2+ 0+ 0+ 0+

KB3 KB3G Exp.

GT strength function calculation could assign the Jπ of the 3.99 MeV state Jπ of the 3.99 MeV state ? νp3/2-νp1/2 gap relatively well known N=32 subshell closure reproduced by KB3 and KB3G interactions 4+ only if 52K g.s. has Jπ=2- non-natural parity state ? strength must fit the feeding Iβ~2% natural parity state: info on f5/2 2+ possible with same (νp3/2)3⊗(νf5/2)1 configuration first 2+ (p3/2⊗p1/2) rules out a possible 1+ (p3/2⊗p1/2) but no E2 transition to g.s.

52Ca

1/2-

Ca

49

Ca

51

Ca

53 5/2- 5/2- 3/2- (5/2-) (1/2-) (3/2-) (3/2-,5/2-) (3/2-,5/2-) (1/2-) 5/2- 5/2- 5/2- 5/2- 1/2- 1/2- 1/2- 3/2- 3/2- 3/2-

Ca

49

Ca

53

Ca

51

Ca

49

Ca

51

Ca

53 5/2- 5/2- 5/2- 5/2- 3/2- 3/2- 3/2- 1/2- 1/2- 1/2- 5/2-

3.50 2.93 2.38 1.72 2.02 3.59 4.07

3/2-

3.80 2.16 1.57 3.84 3.79 1.81 2.79 2.28 2.22 3.89 3.44 1.82 2.82 2.12 1.61 1.03 2.16 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

KB3G Exp. KB3 (~GXPF1)

Comparison Exp. vs. Theory for odd Ca isotopes

β decay of the N=33 55Ti nucleus consistent with a 5/2- g.s. Jπ assignment depends on interaction above 2.5 MeV Results support KB3G with a more attractive p3/2-f5/2 lower part of fp shell well known

49Ca: good agreement between

experiment and theory

51Ca: preliminary results 53Ca:

good agreement for lowest states 2.22 MeV state: Jπ=3/2- better overlap with 53K g.s. configuration 1/2+ or 3/2+

Mantica et al., Phys. Rev. C 68,044311 (2003)

p1/2 and f5/2 orbitals very close 5/2- state too high with KB3

analysis of 53K experiment (july 03) to complete decay scheme (n,γ) new neutron transitions observed but statistics very low

Conclusions Perspectives

new neutron transitions observed decay of 53K: we have measured the decays of 52K, 52K and 52K at CERN using efficient n and γ detection experimental data: decay of 52K: new T1/2, P1n and P2n values for 52K GT strength calculation to locate non-natural parity states calculations: tuning of n-n interaction in fp shell: evolution of p1/2-f5/2 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 54K 54Ca refine neutron spectroscopy for 52K decay (Ex, feedings) 11 new transitions identified 3 new transitions identified 2 new low energy neutron transitions to 51Ca g.s. ~10 new n-γ coincidences (mainly to 1.72 and 2.38 MeV states)

Many thanks to all my colleagues from Geneva, Bucharest, Caen, Constantine and Strasbourg who have made this work possible

• P. Dessagne
• A. Buta
• G. Heitz
• F. Benrachi
• S. Courtin
• S. Grévy
• C. Borcea

J.C. Caspar J.C. Angélique

• F. Perrot
• F. Negoita
• P. Baumann
• M. Ramdhane
• N. Orr
• G. Ban

F.R. Lecolley

• I. Stefan
• C. Jollet
• D. Etasse
• F. Nowacki
• E. Caurier
• G. Le Scornet
• E. Poirier
• C. Miehé
• E. Liénard

the IReS (Strasbourg) workshop and the ISOLDE collaboration.