Shatendra K. Sharma

WORK ON PHOTON –INDUCED ATOMIC INNER-SHELL X-RAYS
The experimental measurements on the photon induced atomic-inner-shell vacancies and emitted fluorescent X-rays have been made. The parameters like differential and total X-ray production cross-sections, relative x-ray peak intensities; sub-shell radiative decay rates; fluorescence yields of LIII sub-shell /M-shell are measured .The angular distribution of fluorescent X-rays to investigate their anisotropy have also been measured. The measurements of above parameters are of great importance on account of their numerous applications in the fields of radiation physics, atomic physics, nuclear physics, solid state physics, plasma physics, astrophysics and non-destructive testing of samples of biological, geological, archaeological and technological interests. The topic wise description of above work are as under.

X-RAY PRODUCTION CROSS-SECTIONS
The partial L shell x-ray production cross-sections with 59.57 keV photon excitation are measured in elements with atomic number 73  Z  92. The measurements have been made in a 90 reflection geometry with 241Am as source of 59.57 keV gamma rays. The measured cross-sections are also compared with the theoretical calculations in the form of relative intensities I(L )/I(L), I(L )/I(L ) and I(L )/I(L ). The results have been interpreted in terms of photo-ionisation cross-sections, fluorescence yields, Coster-Kronig transition probabilities and radiative decay rates.

ENERGY DEPENDENCE OF L-SHELL X-RAY RELATIVE INTENSITIES
The energy dependence of L shell x-ray relative intensities of some high 'Z' elements has also been investigated in the photon energy region of 14  E  44 keV. The external conversion K x-rays of elements in the region 37 Z  64 induced by 60 keV photons from 1 curie 241Am source in a double reflection geometry. The results of such measurements are compared with the calculated values using the sub-shell photo-ionisation cross-sections, fluorescence yield and radiative and non-radiative decay rates. It has been established from above results that unlike K shell, the L shell relative intensities are not independent of photon energy.

THE LIII SUB-SHELL DECAY RATES
The LIII sub-shell relative radiative decay rates in Pb Th and U by selective ionisation of LIII sub-shell are also measured. The technique of selective ionisation using radioactive sources has been used for the first time to determine above decay rates. As no other experimental data for LIII sub-shell radiative decay rates are available, the measured values are only compared with the theoretical values and found to show a good agreement.

ANISOTROPY OF PHOTON INDUCED X-RAYS
The experiments are carried out to investigate the theoretical prediction of Flugge et al (1972)about the anisotropic emission of radiation from the states with J1/2 .The measurements of sub-shell relative intensities of resolved peaks are made at emission angle varying from 60o to 150o at 10o intervals. The above measurements have revealed for the first time that x-rays originating from the states J1/2 (e.g.LIII sub-shell J=3/2) and falling under L and L peaks show an anisotropic angular distribution. However, the peak L and L do not show any measurable anisotropy. These results, though in conformity with the predictions of Flugge et al (1972) cannot be compared with other results as no other experimental or theoretical data are available.

M –SHELL FLOURESCENT YIELDS
The average M shell fluorescence yields have also been measured for some high 'Z' elements. The M-Shell vacancies are produced by photo ionisation with 5.597 keV Mn X-rays emitted from 55Fe radioactive source. The values of measured M-shell x-ray production cross-sections are used to determine using the theoretical values of M-shell photo ionisation cross-sections from Scofield (1973). The results are compared with other data wherever available and in some cases the calculations for are made from the available theoretical data. It is also observed that the average fluorescence yields are independent of initial vacancy distribution among its sub-shells.