Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

Nuclear Sciences 492.3 Atomic Physics2.3.1 Sub-shell Ionisation2.3.1.1 The effect of multiple ionization on L subshell ionization of Au and U by 5-10 MeV C and Si ionsC +q and Si +q (q = 3, 4) ions in the energy range 5 10 MeV obtained from the Pelletron Accelerator,IOP, Bhubaneswar, were used to bombard thin W, Au and U targets to excite L X-rays. A Si(Li)detector having an energy resolution of 160 eV at 5.9 keV were used to detect these X-rays. Tomeasure the efficiency of the Si(Li) detector and to calibrate the system very accurately, thintargets of KBr, Ni, Zn, Sr, Mo, Ag and Sn targets were bombarded with 3 MeV proton beam.Back scattered particles were measured with a Si surface barrier detector simultaneously with theX-rays so as to avoid the error in target thickness measurements. Energy resolved peaks of L α , L β, L γ etc. lines excited by C and Si ions can be easily observed. When these spectra are comparedwith those induced by protons, shifting of the peak position towards the higher energy side andwidening of the peaks are observed. This is a clear signature of the multiple ionization. Evaluationof the subshell ionization cross sections and the extent of multiple ionization are in progress.D Mitra, S Santra, AC Mandal, M Sarkar, D Bhattacharya, G LapickiNAP2.3.1.2 Measurements of the angular distribution of L X-rays of Au and U in photoionisationLast year, a set of data was taken on the angular distribution of L X-rays of Au and U excited by a109 Cd source. When these data were thoroughly analysed, it was observed that at some points thedata had to be re-measured. In order to have a fresh set of data, we decided to repeat the wholeexperiment. Before going into the main experiment, an 241 Am source of 1 µCi was placed on anAl frame fixed at the centre of the angular distribution Table. With a Si(Li) detector, the L lines (which are isotropic in nature) emitted from the source were detected over the angular range from40 o to 140 o . The anisotropy of these lines are found to be 2% due to the misalignment of the table.Au and U foils were held vertical to the table with the help of the Al frame. The 109 Cd sourcewith the graded collimator was placed near the centre of the table so that the emerging X-raysfrom the source make an angle of 60 o with the normal to the foils. Keeping the source and thetarget positions fixed, the detector was moved to scan the whole angular range. Data were thenanalysed. It was observed that for Au, the angular anisotropy of the emitted L lines are within5% while for U it is within the experimental error. Our observation contradict the results of thegroups of Patiala, India and that of Turkey but are in agreement with the findings of the groupsof Chandigarh and Japan.S Santra, D Mitra, M Sarkar, D Bhattacharya, PK DasNAP2.3.1.3 Numismatic StudyIn collaboration with the Centre for Archaeological Studies and Training (CAST) Kolkata, 15 silvercoins have been analysed with our EDXRF system. These coins were from the period of 1200 AD.