Sum-Up and Pile-Up Contribution to Cross-Over Peaks in Coincidence gamma Spectroscopy

High-efficiency arrays for γ spectroscopy, now available in several Laboratories, make possible the measurement of very weak cross-over transitions of high potential interest. A limit to the measurement possibilities comes, however, from the simultaneous detection of two γ-rays of a stop-over cascade (or “sum-up”), which cannot be distinguished from the true detection of the cross-over transition. We propose a new method to measure (and correct for) the sum-up effect, which can be used with symmetric γ detector arrays (like GASP and GAMMASPHERE), and discuss the possible techniques for identifying and estimating quantitatively the contribution of random pile-up, which can be sizeable at high counting rate. These ideas have been experimented at GASP in a dedicated measurement with a radioactive source of View the MathML source. The results of this measurement are presented and discussed. Moreover, as a significant example, the method is applied to deduce the intensity of the E3 cross-over transition from the lowest 3− state of View the MathML source.