Registration of gamma radiation from the 133Ba and 134Cs decay by detectors of the Pripjat system

Three NaI(Tl) detectors of 10 cm x 15 cm, in pairs and the three-detector system, were used to acquire spectra of 133Ba and 134Cs, and to consider registration of gamma radiation from de-excitation of their daughters (133Cs and 134Ba, respectively). The sources were measured for 7200 seconds real time (detector pairs) and 10 000 seconds real time (three-detector system) in the non-coincident mode of counting, as well as in the modes of double and triple gamma coincidences. Based on the photopeak detection efficiencies, minimum detectable activity and ratios of counting rates in the source and background spectra for individual detectors, the non-coincident mode is found to be optimal for 133Ba detection via the 356 keV gamma peak, whereas the mode of double coincidences is found to be optimal for 134Cs detection via the 605 keV and 796 keV gamma peaks.