Double internal conversion in ^137𝑚Ba

Full text: Following on from recent work on double gamma emission in ^137𝑚Ba, interest was raised in investigating the double internal conversion process in the decay of ^137𝑚Ba. There is some controversy over the expected rates of double conversion with respect to the double gamma emission rates in the literature. Work at the ANU has be undertaken to measure the double internal conversion rate and to compare with the theoretical predictions in order to resolve these controversies. Electron-electron coincidences from a ¹³⁷Cs source have been measured using the Superconducting Electron Spectrometer (Super-e) with an array of Si detectors (i.e. in the pair spectrometer mode) to determine the double internal conversion rate. In addition to an experimental determination of the double internal conversion rate, the theoretical description of double internal conversion has been advanced. Building on the work of Grechukhin, the double differential cross section for double internal conversion has been derived. The total rate and the double differential cross section have been calculated. Results of the experiment will be the reported along with the theoretical predictions. (author)