Feb 12 – 14, 2007
Europe/Zurich timezone

Evolution of nuclear shell structure with neutron excess in the fp-shell

Feb 13, 2007, 11:00 AM
Council Chamber, 503/1-001 (CERN)

Council Chamber, 503/1-001



Prof. Bogdan Fornal


The evolution of properties of atomic nuclei with respect to increase in neutron richness is one of the crucial issues in the modern nuclear structure studies. In particular, neutron-rich nuclei above the doubly magic 48Ca have recently attracted a lot of interest due to an N=32 subshell closure that was evidenced in 52Ca, 54Ti and 56Cr. This phenomenon was attributed to the strong proton f7/2 - neutron f5/2 monopole interaction, which causes an increase in energy of the f5/2 single particle orbital with respect to the p3/2 and p1/2 levels as protons are subtracted from the f7/2 shell. However, the magnitude of this increase, particularly in Ca isotopes, is difficult to detect as the states involving the neutron f5/2 orbital in such nuclei like 51-53Ca are very hard to reach. In our recent experiments we studied neutron-rich species close to Z=20 using deep inelastic processes occurring in heavy ion collisions of a 48Ca beam on a 238U target. In one measurement, a thick target technique was applied and the gamma coincidence data were collected with GAMMASPHERE at Argonne NL. In the second experiment, the same reaction was studied employing the PRISMA+CLARA detection system at LNL in Legnaro. With A and Z reaction fragment identifications obtained from PRISMA, we were able to assign the observed (with CLARA) gamma transitions to a given product. These transitions were subsequently used as “starting points” in the analysis of thick target gamma coincidence data. Among many findings, yrast structures in the N=31 isotones, 52Sc and 51Ca were located - these structures include excitations involving f5/2 neutrons. The presentation will discuss new results in light of shell model calculations and theoretical predictions for the f7/2 – f5/2 monopole interaction strength arising from the tensor component of the nucleon-nucleon interaction.

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