L x-ray production cross sections in Th and U at 17.8, 25.8 and 46.9 keV photon energies

The L x-ray production (XRP) differential cross sections in Th and U have b een measured at the 17.8 keV incident photon energy (E-L3 < E-inc < E-L2, E -Li is the Li subshell ionization threshold) in an angular range 90 degrees -160 degrees, and at the 25.8 and 46.9 keV incident photon energies (E-L1 < E-inc < E-K) at an angle of 130 degrees. The measurements were performed using the energy dispersive x-ray fluorescence set-up in secondary excitati on mode. In contrast to the findings of an earlier experiment (Sharma and A llawadhi 1999 J. Phys. B: At. Mel. Opt. Phys, 32 2343), the present measure ments rule out the possibility of a strong angular dependence of differenti al cross sections for various L-3 subshell x-rays following selective photo ionization of the L-3 subshell. Integral L XRP cross sections at the 17.8, 25.8 and 46.9 keV photon energies, deduced assuming isotropic emission of t he L x-rays, are found to be in good agreement with those evaluated using t he most reliable theoretical values of L-i (i = 1, 2, 3) subshell photoioni zation cross sections, fluorescence yields, x-ray emission rates and Coster -Kronig transition probabilities.