Low level gamma spectrometry by beta–gamma coincidence

A beta–gamma coincidence system consisting of a 2π plastic beta detector and a Ge(Li) detector, is described. Such a system allows for a drastic reduction of background (not, vert, similar70 times) as well as of Minimum Detectable Activity (not, vert, similar7 times). An integral background (50–1500 keV) of less than 0.1 cps is obtained. The difficulty of the method, otherwise simple and inexpensive, is the precise determination of beta detector efficiency.