Evolution of nuclear spectroscopy at Saha Institute of Nuclear Physics

Experimental studies of nuclear excitations have been an important subject from the earliest days when the institute was established. The construction of 4 MeV proton cyclotron was mainly aimed to achieve this goal. Early exp eriments in nuclear spectroscopy were done with radioactive nuclei with the help of beta and gamma ray spectrometers. Small NaI(TI) detectors were use d for gamma-gamma coincidence, angular correlation and life time measuremen ts. The excited states nuclear magnetic moments were measured in perturbed gamma-gamma angular correlation experiments. A high transmission magnetic b eta ray spectrometer was used to measure internal conversion coefficients a nd beta-gamma coincidence studies. A large number of significant contributi ons were made during 1950-59 using these facilities. Proton beam in the cyc lotron was made available in the late 1950's and together with 14 MeV neutr ons obtained from a C-W generator a large number of short-lived nuclei were investigated during 1960's and 1970's. The introduction of high resolution Ge gamma detectors and the improved electronics helped to extend the spect roscopic work which include on-line (p, p '-gamma) and (p, n gamma) reactio n studies. Nuclear spectroscopic studies entered a new phase in the 1980's with the availability of 40-80 MeV alpha beam from the variable energy cycl otron at VECC, Calcutta. A number of experimental groups were formed in the institute to study nuclear level schemes with (alpha, xn gamma) reactions. Initially only two unsuppressed Ge detectors were used for coincidence stu dies. Later in 1989 five Ge detectors with a large six segmented NaI(TI) mu ltiplicity-sum detector system were successfully used to select various cha nnels in (alpha, xn gamma) reactions. From 1990 to date a variety of medium energy heavy ions were made available from the BARC-TIFR Pelletron and the Nuclear Science Centre Pelletron. The state of the art gamma detector arra ys in these centres enabled the Saba Institute groups to undertake more sop histicated experiments. Front line nuclear spectroscopy works are now being done and new informations are obtained for a large number of nuclei over a wide mass range. Currently Saha Institute is building a multi-element gamm a heavy ion neutron array detector (MEGHNAD), which will have six high effi ciency clover Ge detector together with charged particle ball and other acc essories. The system is expected to be usable in 2002 and will be used in e xperiments using high energy heavy ions from VECC.