Prem Singh

Li (i=1,2,3) subshell X-ray production cross-sections and fluorescence yields for Ir, Pt, Pb and Bi

Abstract The L i ( i =1,2,3) subshell X-ray production (XRP) cross-sections were measured for 77 Ir, 78 Pt, 82 Pb and 83 Bi following direct ionization in the L i ( i =1,2,3) subshells by the 59.54 keV γ-rays and the L 3 subshell by the Br/Rb/Sr/Y K X-rays. The photon sources consisting of an 241 Am source in (i) the direct excitation mode and (ii) the secondary excitation mode together with the KBr/RbNO 3 /SrCO 3 /Y secondary exciter and an Si(Li) detector were used. The L i ( i =1,2,3) subshell fluorescence yields ( ω i ) for these elements were deduced using the measured XRP cross-sections and the L i subshell photoionization cross-sections based on the Hartree–Fock–Slater model. The measured ω 1 values are found to be higher upto 50% than those based on the relativistic Dirac–Hartree–Slater (RDHS) calculations, while the ω 2 and ω 3 values exhibit good agreement. The predicted jump in the RDHS based ω 1 values from 77 Ir to 78 Pt due to onset of intense L 1 –L 3 M 4 CK transition is not observed.

L1–L3 Coster–Kronig yield for Ir, Pt and Bi

The L1–L3 Coster–Kronig yield, f13, for 77Ir, 78Pt and 83Bi was determined using measured intensities of the Lα X-rays following photoionisation in the Li (i=1,2,3) subshells in different proportions by the 59.5 keV γ-rays and the characteristic K X-rays of the Br/Sr/Y elements. The measurements involved an Si(Li) detector and photon sources consisting of an 241Am source used in (i) the direct excitation mode and (ii) the secondary excitation mode together with the KBr, SrCO3 and Y secondary exciters. The measured values of the f13 yield are 0.467±0.025, 0.527±0.027 and 0.620±0.025 for 77Ir, 78Pt and 83Bi, respectively. These values are found to be substantially smaller than those based on the relativistic Dirac–Hartree–Slater calculations.