Standardization of 241 Am by means of coincidence system using 4π plastic scintillator detector

A 4π (α,β)-γ coincidence system using a plastic scintillator detector in 4π geometry has been developed and applied for the standardization of 241 Am. The scintillator shape and dimensions have been optimized for maximum charge particle detection efficiency, while keeping background low and a nearly constant gamma ray efficiency for different points at the radioactive source. The gamma ray events were measured with 3x3NaI(Tl) scintillation counter. The electronic system for processing pulses consisted of logic gates and delay modules feeding a Time to Amplitude Converter with output to a Multichannel Analyser. The alpha detection efficiency measured with 241 Am resulted around 95% and the beta detection efficiency measured with 60 Co was around 60%. Activity measurements of 241 Am were compared with a conventional system employing a 4π proportional counter and showed good agreement. (author)