Evolution of Nuclear Structure with the Increase of Neutron Richness – Orbital Crossing in Potassium Isotopes W. Królas, R. Broda, B. Fornal, T. Pawłat, J. Wrzesiński Department of the Structure of Atomic Nucleus (NZ22/NO2)

Evolution of Nuclear Structure with the Increase of Neutron Richness Changes in shell structure – rearrangements of orbitals Vanishing of shell gaps, appearance of new „magic numbers” Experimental evidence needed Experimental challenge – nuclei not easily accessible

Shell structure in neutron-rich nuclei Shell quenching; new gaps Changes in (effective) interactions Structure of doubly magic nuclei

Evolution of Nuclear Structure for neutron-rich nuclei around 48 Ca f 7/2 p 1/2 f 5/2 p 3/2 πf 7/2 πd 3/2 s 1/2 Z=20 N=28 Changes of relative πs 1/2 –1, πd 3/2 –1 and πd 5/2 –1 single particle energies 4 T. Otsuka et al., PRL 95, (2005) 48 Ca

Neutron-rich nuclei produced in deep-inelastic processes Beams of heavy-ions at energies above the Coulomb barrier Transfer of nucleons – trend to equilize N/Z ratio Population of Yrast states in final fragments

Thick target experiments 4 R. Broda et al., JPG 32, 151 (2006) 4 W. Królas et al., NPA 724, 289 (2003) Fragments stopped in the target, no isotopic identification Aquisition of high statistics  -  coincidence data sets Level structure from coincidence analysis, ID from cross-coincidences and/or known transitions GAMMASPHERE

Recent results around 48 Ca f 7/2 p 1/2 p 3/2 πf 7/2 πd 3/2 s 1/2 Z=20 N=28 52,53,54,56 Ti: 4 B. Fornal et al., PRC 72, (2005), PRC 70, (2004) 4 S.N. Liddick et al., PRL 92, (2004) 4 R.V.F. Janssens et al., PLB 546, 55 (2002) 49,50 Ca and 51 Sc: 4 R. Broda at al., APPB 36, 1343 (2005), and to be published 47,48,49 K: 4 R. Broda et al., 4 W. Królas et al., to be published

New experimental opening Thick target data insufficient: difficult isotopic identification, fast gamma transitions unobserved PRISMA spectrometer designed for identification of deep-inelastic reaction fragments PRISMA

PRISMA spectrometer A magnetic heavy ion spectrometer designed to fully identify (A, Z) fragments deflected at large angles CLARA: an array of 24 Clover detectors 238 U MeV 48 Ca Complementary sets of data: PRISMA – (A,Z) identification, fast  transitions and GAMMASPHERE –  -  coincidence data

Shell model description of neutron-rich Potassium isotopes 48 Ca double closed-shell configuration For Potassium (Z=19): a proton-hole, nearest shells are  s 1/2,  d 3/2 and  d 5/2 For neutron-rich (N > 28): neutrons in p 3/2, p 1/2 and/or f 5/2 shells

Evidence of a 7/2 – isomer in 47 K 1660 M2 1/2 + 3/ keV line not in prompt gamma spectrum, assigned as an M2 isomeric transition: 7/2 –  3/2 + 7/2 – isomer, T 1/2 = 7 ns

Shell model configurations in 48 K 47 K 28 πs 1/2 –1 πd 3/2 –1 πf 7/2 + νp 3/2 1–1– 2–2– 2–2– 0–0– 1–1– 3–3– K 29 πf 7/2 υp 3/2 πs 1/2 –1 υp 3/2 πd 3/2 –1 υp 3/2

First experimental identification of excited states in 48 K PRISMA GAMMASPHERE Identification of 48 K gamma lines from PRISMA Level scheme established from GAMMASPHERE coincidence data New 6.5 ns isomer placed in 48 K

New excited states and their configuration assignment in 48 K (1 – ) (3 – ) (5 + ) 6.5ns πf 7/2 υp 3/2 πs 1/2 –1 υp 3/2 πd 3/2 –1 υp 3/2

First observation of excited states in 49 K Gamma lines identified from PRISMA Level scheme from coincidence analysis πf 7/2 πs 1/2 –1 πd 3/2 –1 PRISMA

Energies of lowest 1/2 +, 3/2 + and 7/2 – states in odd K isotopes /2 + MeV / /2 – 39 K K K K K K 30 excitation energy

Evolution of relative πs 1/2 –1 and πd 3/2 –1 proton single particle energies As neutrons occupy the f 7/2 orbital, proton orbitals are shifted – interaction f 7/2 ↔  d 3/2 is attractive, f 7/2 ↔  s 1/2 is repulsive πs 1/2 –1 πd 3/2 – 1 MeV N= This behaviour consistent with the predicted monopole effect of the tensor force

Summary Strong research program on spectroscopy of neutron-rich nuclei in the vicinity of 48 Ca is being pursued at IFJ PAN New possibilities are offered by complementary analysis of PRISMA spectrometer and  -  coincidence experiments Established evolution of proton single particle energies in Potassium isotopes shows rearrangement of single particle orbitals in neutron-rich nuclei

Kraków group and collaborators R. Broda, B. Fornal, W. Królas, T. Pawłat, J. Wrzesiński IFJ PAN Kraków S. Lunardi, A. Gadea, N. Marginean, L. Corradi, A.M. Stefanini, F. Scarlassara, G. Montagnoli, M. Trotta, D. Napoli, E. Farnea Laboratori Nazionali di Legnaro and INFN Padova R.V.F. Janssens, M.P. Carpenter, T. Lauritsen, D. Seweryniak, S. Zhu Argonne National Laboratory