Research

For the study of nuclear spectroscopy, the emphasis has mainly been on the study of high spin structure of vibrational nuclei and nuclei near shell closure. The systematics of high spin levels in nuclei in the mass region ~ 75, ~ 90, ~ 120, ~ 130 and ~ 160 have been carried out in the last few years to investigate the interplay of single particle, vibrational and rotational degrees of freedom and the co-existence of these structures.

A systematic study of nuclei near N=50 shell closure was carried out to understand the evolution of high spin structure in these nuclei. In contrast to nuclei near Z=50 shell closure, measurements in ^92,93,94,95Tc, ^95,96,97,98Ru and ⁹⁵Rh indicate that these nuclei do not develop any rotational behaviour at high spin. The low lying levels of these nuclei are well described in terms of large basis shell model calculations using the f-p-g valency nucleons. These calculations have been extended by incorporating proton and neutron core excitation in a truncated model space. Calculations indicate that the levels up to J ~ 22 ħ and E^* ~ 10 MeV can be attributed to the breaking of the N=50 core. Similar effects of core breaking for N=82 shell has been observed for the nucleus ¹⁴⁹Dy. In contrast to N ~ 50 nuclei where the high spin structure is single particle in nature, the Z=50 nucleus ¹¹¹Sn shows a rotational band at high spin. The transitional nuclei ⁹⁹Rh and ¹⁰⁰Pd have been observed to have a well-defined rotational behaviour.

An extensive measurement of the transitional nuclei near A ~ 120 has been carried out using the GDA facility. High spin structures of the nuclei ¹²⁰X, ^{116,118,119,121}Te and ^118,120I have been established. A systematic study of Te isotopes indicated the fully aligned P[(g_9/2)²]6⁺N[(h_11/2)²]10⁺ non-collective oblate configuration in ^116,118Te.

The high spin structures of odd-odd Lu nuclei have been extensively studied. The energy levels of ¹⁶⁴Lu through γ-spectroscopy have been established for the first time. Two strongly coupled bands were identified and tentatively assigned the configurations Ph_11/2 [523]7/2^- Ni_13/2 [642]5/2⁺ and Ph_11/2 [523]7/2^- Nh_9/2 [521]3/2^-. The above assignments are consistent with the observed crossing frequencies, alignments and B(M1)/B(E2) ratios as compared to the neighbouring odd A nuclei. Measurements were also carried out for other odd-odd isotopes of Lu (^162,168,170Lu) which show a gradual reduction of signature splitting with increasing neutron number.

Life time measurements in the γ-soft region (A ~ 70-80) have indicated a rapid change of nuclear shape with rotation and the shape polarisation effect of the occupied g_9/2 proton and neutron orbitals. Identical bands have been observed in the nuclei ⁷⁸Kr and ⁸⁰Rb. The unravelling of the low spin structure, particularly the -ve parity sidebands, was facilitated by the use of the recoil mass separator.

A new high spin isomer (35/2^-) with a life time of 8.6 ± 1.3 ns has been identified in ¹⁵³Eu. Measurement of quadrupole moments of several nuclei have been carried out using the DSAM, RDM and hyperfine interaction studies. The current emphasis is on complete nuclear spectroscopy using information from γ-γ, e-γ and life time measurements.