Determination of minimum detectable activity for underwater radiation detection system

Abstract

An underwater Cs-137 (662 keV) and I-131 (364 keV) radioisotopes monitoring system has been developed using a 3 '' x 3 '' NaI(Tl) detector. To estimate the minimum detectable activity and Bq/L conversion factor, an experiment was first conducted with Ga-68 (511 keV) in a water tank. For energy spectrum comparison, Monte Carlo simulations were performed for Ga-68, Cs-137, and I-131 to determine the conversion factor. The minimum detectable Cs-137 and I-131 activities for the system are 0.77 and 0.89 Bq/L, respectively.