1. a Department of Physics , Calcutta University , 92, Acharya Prafulla Chandra Road, Calcutta, 700 009, India
2. b Scottish Church College , Calcutta, 700 006, India
3. c R. K. Mission Vidyamandira , Belur, W. B., India
4. d Saha Institute of Nuclear Physics , Calcutta, 700 009, India