Multigamma-ray calibration sources

Abstract

We have calibrated a self-consistent set of multigamma-ray standards using the automated multi-spectrometer γ-ray counting facility at LLNL's Nuclear Chemistry Division. Pure sources of long-lived activity were produced by mass separation and,or, chemical purification. The sources were counted individually and in combination on several different calibrated spectrometer systems. These systems utilize various detectors ranging from small (x-ray) detectors to large volume high-purity Ge detectors. This has allowed the use of the most ideal individual detector-efficiency characteristics for the determination of the relative γ-ray intensities. Precise energy measurements, reported earlier (Meyer, 1976) have been performed by an independent method. Both the energy and γ-ray-emission probabilities we determine compare well with independently established values such as the recent ICRM intercomparison of 152Eu. We discuss our investigations aimed at resolving the shape of the efficiency response function up to 10 MeV for large volume Ge(Li) and high-purity Ge detectors. Recent results on the γ-ray-emission probabilities per decay for 149Gd and 168Tm multigamma-ray sources are discussed. For 168Tm, we deduce a 0.01% β − branch to the 87.73-keV level in 168Yb rather than the previous value which was a factor of 200 greater. In addition, we describe current cooperative efforts aimed at establishing a consistent set of data for short-lived fission products. Included are recent measurements on the bromine fission products with γ rays up to 7 MeV.