N. Govinda Nayak

K fluorescence yield measurements in rare earth and heavy elements

K fluorescence yields were measured for 16 elements Cu, Mo, Ag, Cd, Sn, Pr, Sm, Gd, Dy, Ho, Yb, Ta, W, Pb, Th and U using a HPGe low energy photon detector employing the reflection geometry set-up. The target atoms were excited using 59.5 keV and 279.2 keV gamma rays from Am-241 and Hg-203 radioactive sources of strengths 20 mCi and 40 mCi respectively. An effective shielding arrangement was used to minimize the background and multiple scattering. Elemental foils of uniform aerial density and purity better than 99.9% were used as targets. The data were recorded in a 4K multichannel analyser. Among the K fluorescence yields measured in this work nine cases constitute the first measurement. The results are compared with the literature experimental values for available cases and also with the semiempirical fits and theoretical predictions.

Effective atomic numbers of some polymers and other materials for photoelectric process at 59.54 keV

Effective atomic numbers (Zeff) of three polymers, an alloy, a compound and an element have been determined for photoelectric process at 59.54 keV from the accurately measured total attenuation coefficients, for γ ray attenuation. Possible conclusions are drawn on electron binding effects and K-edge effects.

AFM studies of swift heavy ion and electron irradiated mixed barium strontium borate nonlinear optical crystal

Abstract Single crystals of novel nonlinear optical material of mixed barium strontium borate is grown in our laboratory by employing the low-temperature solution technique. Equal proportion (1:1 molar ratio) of AR grade barium borate and strontium borate are mixed together in double distilled water to prepare a supersaturated solution. The solution is allowed to evaporate at constant temperature (30°C) in a Petri dish for about a week which resulted in the formation of seed crystals. These seed crystals are used to grow larger crystals by suspending them using fine silk thread in the supersaturated mother solution. The solution is allowed to evaporate at constant temperature. This resulted in the growth of good transparent crystals of dimension 15 mm ×10 mm ×1 mm after about one month. These crystals show good second harmonic generation (SHG) efficiency. The mixed barium strontium borate crystal is found to be a promising nonlinear optical crystal, which possibly can be used for fabrication of photonic devices. The single crystals of mixed barium strontium borate are irradiated by 120 MeV Ag +13 swift heavy ions (SHI) of fluence 5×10 11 ions / cm 2 at Nuclear Science Centre, New Delhi and also by electrons of 8 MeV energy with a fluence 5.7×109/cm2 using Microtron accelerator at Mangalore University. Surface morphology studies of these crystals are carried out using atomic force microscope. The AFM topographical images of these SHI/electron irradiated single crystals of mixed barium strontium borate are obtained from different frames of the sample taken at different magnifications using atomic force microscope. An attempt is made to explain the surface damage caused due to SHI/electron irradiation using the observed AFM images.

Verification of incoherent scattering functions at intermediate photon momentum transfer

Experimental whole atom differential incoherent scattering cross sections were measured for Cu, Mo, Ag, Cd, Sn, Pr, Sm, Gd, Dy, Ho, Yb, Ta, W, Th and U for the 90 degrees scattering of 145.4 and 84.3 keV gamma rays. The scattering experiments were conducted in a reflection geometry set up with a graded shielding arrangement. A 133 cm3 HpGe detector was used to detect the scattered gamma rays. The cross sections were measured using Al as standard. From the measured cross sections the incoherent scattering functions were extracted. The results are compared with theory and with the experimental values reported in literature for available cases. The electron binding effects and the validity of the incoherent scattering functions at intermediate momentum transfer are discussed.