Absolute radioactivity measurements by the use of a 4pibeta-4pigamma detector configuration.

The radioactivity of 60Co and 134Cs sources were measured using a 4πβ–4πγ detector configuration with a well-type NaI(Tl) crystal and a sandwich type 4πβ detector composed of two sheets of NE102A plastic scintillator coupled to a slender photomultiplier tube. The β-detector was inserted into the well of the γ-detector. Since counting efficiencies in both the β- and γ-channels can be kept high, excellent counting statistics were attainable even when weak sources were measured. This configuration can also be used for radioactivity measurements based upon the direct integral counting of 4πβ+4πγ logic sum signals, and two independent results can be obtained for every measurement. This technique is especially useful for the standardization of complex decaying nuclides.