Primary activity measurements with a 4πβ–4πγ coincidence counting system

The radioactive concentrations of 166mHo, 134Cs and 133Ba solutions have been standardised using a 4πβ–4πγ coincidence counting system we have recently set up. The detection in the beta channel is performed using various geometries of a UPS-89 plastic scintillator optically coupled to a selected low-noise 1 in. diameter photomultiplier tube. The light-tight thin capsule that encloses this beta detector is housed within the well of a 5 in.×5 in. NaI(Tl) monocrystal detector. The beta detection efficiency can be varied either by optical filtering or electronic discrimination when the electrons loose all their energy in the plastic scintillator. This 4πβ−4πγ coincidence system improves on our 4πβ(PC)–γ system in that its sample preparation is less labour intensive, it yields larger beta- and gamma-counting efficiencies thus enabling the standardisation of low activity sources with good statistics in reasonable time, and it makes standardising short-lived radionuclides easier. The resulting radioactive concentrations of 166mHo, 134Cs and 133Ba are found to agree with those measured with other primary measurement methods thus validating our 4πβ−4πγ coincidence counting system.

► A 4πβ(PS)–4πγ coincidence system was developed. ► This system was successfully used to standardise 166mHo, 134Cs and 133Ba solutions. ► Unlike 4πβ(PC)–γ set-ups, its source preparation is cheap and it yields larger efficiencies. ► It also makes standardising short-lived radionuclides easier.