Development of HPGe detector based in-vivo monitoring system for workers handling actinides

Actinides are α emitters followed by low yield, low energy γ/x-rays, therefore measurement of internally deposited actinides is difficult in workers at desired detection level. At present 25 cm dia. x1.2 cm thin NaI (Tl) inside steel room is used for in-vivo monitoring of workers at H.P. Lab. Tarapur. In the case of intake of mixture of radionuclides, due to limitation in its energy resolution and higher background, identification and quantification of radionuclides become difficult.Therefore, a twin HP Ge detector-based actinide-monitoring system is developed for the in-vivo monitoring of workers handling low energy photon emitters (LEPs, Eγ < 200keV) like Pu/Am, nat. U etc. HPGe detectors (p-type) of crystal dimension 91.3 mm dia. x 31.3 mm thick inverted U-type low background cryostat with preamplifiers and 13 L LN2 Dewar were procured from M/s Baltic Scientific Instruments. Both the detectors have 45% relative efficiency and 0.8 mm thick low background carbon epoxy entrance window to allow maximum transmission of photons above 10 keV. These detectors are provided with individual electronics components like preamplifiers and 16 k digital multi-channel analyzers for signal processing