Abstract
An extension of 4πe·X-γ coincidence technique is described to measure the absolute disintegration rate of85Sr.This nuclide shows electron capture-gamma decay, and 514 keV level of85Rb is a meta-stable state with half life of 0.958μsee. Therefore, the conventional 4πe⋅X-γ coincidence technique with about 1μsec of resolution time can not be applied to this nuclide. To measure the absolute disintegration rate of this, the delayed 4πe⋅X-γ coincidence technique with two different resolution times has been used. The disintegration rate was determined from four counting rates of electron-X ray, gamma ray and two coincidences, and the true disintegration rate could be obtained by extra poration of the electron-X ray detection efficiency to 1. Two resolution times appearing in the calculation formulas were determined from the chance coincidence between electron-X ray and delayed gamma ray signals. When the coincidence countings with three different erent resolution time were carried out by one coincidence circuit, the results calculated from all combinations did not agree each other. However, when the two coincidence circuits of the same type were used to fix the resolution time, a good coincidence absorption function was obtained and the disintegration rate was determined with accuracy of±0.5%. To evaluate the validity of the results the disintegration rates were measured by twoNaI (Tl) scintillation detectors whose gamma-ray detection efficiency was previously determined and both results were agreed within accuracy of±0.5%. This method can be applied with nearly same accuracy for the beta-gamma decay nuclide possessing a meta-stable state of the half life below about 10 μsec.
