Production of M x-rays on decay of L3 subshell vacancies to M shell in Pb, Th and U

M shell x-ray production cross sections in thick targets of Pb, Th and U by K x-rays of Rb, Nb and Mo respectively have been measured. As the incident K x-ray energies are above the L3 edge but below L2 edge energies of the respective target elements under reference, the M x-rays are produced not only due to direct interaction of incident photons with M shell electrons but also due to the decay of L3 subshell vacancies to M shell. The measured values have been compared with those calculated using known values of M and L3 subshell photionization cross sections and fluorescence yields etc, wherever possible. (author)