Nuclear Seminar

Studies on nuclear structure on and away from the stability line

Dr. Maitreyee Saha Sarkar
Saha Institute of Nuclear Physics

Monday, August 18, 2008   4:00 p.m.   NSH 124
(Refreshments served prior to seminar in NSH 124)

The seminar will be aimed to discuss some of our recent work. We have performed experimental and theoretical investigations in two regions of the nuclear chart: stable nuclei with N ≈ Z near ⁴⁰Ca and highly neutron-rich ones above ¹³²Sn. In the recent times, India has acquired quite a few Clover detectors to build an Indian National Gamma Array  (INGA). We have used earlier campaigns of this array for gamma spectroscopic studies. Characterisation of Clover detector also forms a part of our study.  Apart from discussing our different work in brief, I shall highlight our new results on neutron-rich isotopes of semi-magic Sn and discuss the experimental characterisation of Clover detectors.

I shall start with our theoretical work in neutron-rich ¹³²Sn region.  Large basis un-truncated shell model (SM) calculations have been done for the A = 138 neutron-rich nuclei above the ¹³²Sn core using two (1+2) - body nuclear Hamiltonians, viz., realistic CWG and empirical SMPN. Calculated binding energies (with SMPN only), excitation spectra, and B(E2) values  are nicely reproduced by both the interactions for even-even A = 138 isobars for which experimental data are available. But the two theoretical results differ dramatically for ¹³⁸Sn, a nucleus on the r-process path. CWG predicts nearly constant energies of the first 2⁺ states for the even-even Sn isotopes above the ¹³²Sn core, normally expected for semi-magic nuclei. But SMPN predicts a remarkable new feature: decreasing first E (2⁺), E(4⁺) energies with increasing neutron number. The predicted energies for the Sn isotopes fit in the systematics for the E (2⁺) energies of their isotones with Z > 50.  This observation provides very useful ingredients for reviewing the problems related to the nuclear astrophysics in general.

The second part of my talk deals with the high-energy (till 11 MeV) characterisation of the Compton suppressed Clover detector. This work has been done as a prelude to our experimental study of mass 40 region using a Clover array. Typical characteristics of a Clover detector like addback factor, hit pattern distribution have been determined. Relative efficiency and the ratios of escape peaks to the full energy peak of Clover in add and addback modes have been compared with those of a standard HPGe detector. In this connection I shall also discuss our preliminary work on the improvement of the background characteristics of normal HPGe and Clover detectors at the low energies.