Badania struktury jąder neutrono-nadmiarowych produkowanych w głęboko nieelastycznych reakcjach ciężkich jonów na wiązkach stabilnych i radioaktywnych

Abstract

A novel experimental method exploiting the production of neutron-rich fragments in deepinelastic heavy ion collisions was used to extend the in-beam γ-ray spectroscopic studies towards previously inaccessible neutron-rich nuclei. The γ-γ coincidence analysis of reaction products was used to obtain new information on the mechanism of deep-inelastic collisions, in particular on the neutron-to-proton ratio equilibration process. These results were compared to theoretical predictions based on a liquid-drop energy minimization model and a heavy ion phase space exploration model. Neutron-rich potassium isotopes were studied in the bombardments of thick 238U and 208Pb targets with the 48Ca beam. Excited states in the 48K and 49K isotopes were identified for the first time in experiments with the PRISMA-CLARA spectrometer. Based on those identifications the level schemes of predominantly yrast excited states were established from the analysis of GAMMASPHERE γ coincidence data collected for the same reactions. A new 5+ isomer was identified in 48K, the analog of the 7/2– isomer in 47K. Important information on the coupling of the proton-hole and neutron-particle states in the neutron-rich 48K and 49K isotopes was obtained. Systematics of lowest 1/2+, 3/2+, and 7/2– states in odd-odd potassium isotopes were extended beyond the N = 28 line. These results confirm a reordering of the s1/2 and d3/2 proton-hole orbitals for neutronrich potassium isotopes which was interpreted in terms of the evolution of single-particle energies caused by the monopole effect of the tensor force. Experimental efforts aimed at the establishing of the yrast excitations in the series of even neutron-rich nickel isotopes reaching toward the double closed-shell 78Ni isotope are described including the search for the missing 8+ isomeric state in 72Ni. In the analysis of the GAMMASPHERE γ coincidence data from experiments with the 76Ge beam the ground-state band in 72Ni was extended to the 8+ state concluding that this level has a half-life not longer than 20 ns. Based on the established level scheme a large enhancement of the B(E2) transition probability for the 8+ → 6+ transition in 72Ni compared to 70Ni was calculated. This effect is compatible with the predictions of the van Isacker model suggesting a significant lowering of the 6+ seniority υ = 4 level which is calculated to be near the 6+ υ = 2 state. Recent spectroscopic results for less exotic even-even nickel isotopes 64, 66, 68Ni are presented including new spin and parity assignments based on the analysis of angular correlations of γ rays emitted from fragments produced in deep-inelastic collisions with the 64Ni beam. Prospects of new studies of neutron-rich nuclei produced in deep-inelastic collisions using radioactive ion beams of fission fragments are also discussed. Basic technical aspects of the production of such beams are described based on the Holifield Radioactive Ion Beam Facility RIB project. The design and construction details of the Isomer-scope detection setup for the identification and spectroscopy of the isomeric decays in fragments produced in deep-inelastic collisions are presented. Results of the test experiment with a stable 71Ga beam performed at HRIBF are shown. Plans for an upgrade of the Isomer-scope device and its future application for experiment at Oak Ridge and elsewhere are discussed.