Thin NaI(Tl) crystals to enhance the detection sensitivity for molten 241Am sources

A thin 5-mm NaI(Tl) scintillator detector was tested with the goal of enhancing the detection efficiency of 241Am gamma and X rays for steelworks operations. The performance of a thin (5 mm) NaI(Tl) detector was compared with a standard 76.2-mm thick NaI(Tl) detector. The 5-mm thick detector crystal results in a 55% smaller background rate at 60 keV compared with the thicker detector, translating into the ability to detect 30% weaker 241Am sources. For a 5 mm thick and 76.2 mm diameter NaI detector in the ladle car tunnel at Outokumpu Tornio Works, the minimum activity of a molten 241Am source that can be detected in 5 s with 95% probability is 9 MBq.