Fluorescence Yields of theLIIandLIIIShells in Heavy Elements

Abstract

A method has been developed to measure the fluorescence yields of the $L_{\mathrm{III}}$ subshells in many heavy elements. This method is closely related to the $K$ to $L$ x-ray coincidence measurements used to determine ${\omega }_{\mathrm{KL}}$, the partial $L$ shell yield following $K$ x-ray emission. The fluorescence yield ${\omega }_{\mathrm{KL}}$ is a linear combination of ${\omega }_{L_{\mathrm{II}}}$ and ${\omega }_{L_{\mathrm{III}}}$, the fluorescence yields of the $L_{\mathrm{II}}$ and $L_{\mathrm{III}}$ subshells. The scintillation counters used to perform the coincidence experiments cannot separate the two components ($K_{\alpha 1}$ and $K_{\alpha 2}$) of the $K_{\alpha }$ x rays, and thus the experiment determines only the average fluorescence yield ${\omega }_{\mathrm{KL}}$. There are a number of elements possessing $K$ absorption edges between the $K_{\alpha 1}$ and $K_{\alpha 2}$ x rays of the target materials. By using one of these elements as a secondary radiator, it is possible to eliminate all pulses in the $K$ x-ray counter due to $K_{\alpha 2}$ x rays. The only target x rays contributing to the coincidence rate are the $K_{\alpha 1}$ x rays which are caused by $L_{\mathrm{III}}\to K$ transitions. The observed coincidence rate is therefore proportional to ${\omega }_{L_{\mathrm{III}}}$. Values of ${\omega }_{L_{\mathrm{II}}}$ can then be computed using previous measurements of ${\omega }_{\mathrm{KL}}$.