Nuclear Seminar

Microsecond Isomer Spectroscopy & Shell Model Studies Using INGA & HIRA

Dr. Sandeep Ghugre
UGC-DAE CSR, Kolkata Centre, India

Thursday, May 11, 2006   4:00 p.m.   NSH 124
(Refreshments served prior to seminar in NSH 124)

 

The Indian National Gamma Array (INGA) is a multi-Clover detector array. A multi-detector array and a recoil separator form a formidable tool for detailed spectroscopic investigation of nuclear structure. This presentation discusses the recoil-tagging technique and its application to investigate the lifetimes of micro-second isomers in the vicinity of N~50 shell closure. The recoiling nuclei from fusion-evaporation reactions are selectively transported to the focal-plane of a recoil separator where the decay of the isomeric level is investigated in a relatively low-background environment. Since the prompt transitions are detected at the target position this method allows us to correlate the feeding and decay pattern of the isomeric level. The half-lives of isomers in ⁸⁸Zr, ^90,91Nb and ⁹⁰Mo were investigated using this technique. New levels were established upon the known 0.47ms isomer in ⁹⁰Nb. The results were compared with the predictions of the large basis shell model calculations. The effects of truncation of the valence space and the systematics of effective charges (e_p and e_n) were qualitatively understood within these calculations. Using the INGA in the standalone mode structure of nuclei around the N=20, 50 and 82 shell closures were studied using the Indian National Gamma Array, a multi-Clover detector array. Some of the interesting results for the neutron-rich N ~ 20 nuclei, have necessitated changes from the earlier reported results, would be discussed.