Investigation of Nuclei Near N = 82 and Z = 64 via Radioactive Decay of High-Spin Isomers

摘要

An island of very high spin isomers was found recently in neutron-deficient Gd-Lu nuclei near the N = 82 closed shell in (H.I.,xn) measurements. This exciting discovery has led to a large number of experiments trying to identify the structures of these isomers and the nuclei in which they occur. These attempts have been helped in many instances by available spectroscopic information at low excitation energies. A systematic investigation of the low-lying structure of nuclei near N = 82 and Z greater than or equal to 64 was carried out. Heavy-ion beams were used to produce proton-rich isotopes which were then transported, with the use of gas-jet systems, to shielded areas where singles and coincidence gamma -ray measurements could be made. Earlier investigations dealt with the decay of terbium ( exp 146-149 Tb) and dysprosium ( exp 147-152 Dy) nuclei. During the past two years the research program was extended to holmium nuclides (A less than or equal to 152) produced in exp 10 B bombardments of samarium. Two new isotopes, exp 149 Ho and exp 148 Ho, were identified. The decay data of 21-s exp 149 Ho supplement in-beam results and locate the hg/ sub 2 neutron state in exp 149 Dy to be at 1091 keV. The most intense gamma -ray associated with 9-s exp 148 Ho has an energy of 1688 keV. It is possibly the first-excited to ground-state transition in exp 148 Dy. Recent in-beam measurements have shown that the first-excited state in exp 146 Gd is, unexpectedly, 3 exp - in contrast to doubly even N = 82 nuclei below gadolinium where it is 2 exp + . It would be interesting to determine whether the 1688-keV level in exp 148 Dy, the next nucleus in this isotonic series, is 2 reverse arrow or 3 exp - in character. 12 references. (ERA citation 04:037708)