Choi, Y.; Ji, Y.-Y., and Joung, S., 2023. Experimental counting efficiency calibration of in situ marine radioactivity monitoring systems in Busan (Korea) based on seawater salinity. Journal of Coastal Research, 39(2), 377–383. Charlotte (North Carolina), ISSN 0749-0208.

In situ underwater gamma-ray spectrometry is an effective method for monitoring marine radioactivity. With in situ measurement, however, it is difficult to calibrate counting efficiency experimentally, and a simulation is thus generally used to calculate the theoretical efficiency without experimental verification. This paper proposes a method to establish experimental counting efficiency by estimating the radioactivity concentration of ⁴⁰K, which is a natural radionuclide emitting a 1,461 keV gamma ray, based on the salinity of seawater. The measurement was performed in a marine monitoring system in Busan equipped with a 3″φ × 3″ NaI(Tl) detector in a tank filled with sampled seawater. The results were compared with the theoretical counting efficiency calculated by simulation to verify the validity of the simulation. The results confirmed the experimental efficiency and theoretical efficiency were in very good agreement. In addition, using the validated simulation, a theoretical efficiency curve according to the gamma-ray energy was obtained. For simpler application, the concept of radioactivity conversion factor in units of s^–1 · Bq^–1 · kg for each peak was proposed. If the ratio of the conversion factor of each peak to the factor of ⁴⁰K is obtained, the conversion factors for artificial radionuclides, which are difficult to measure practically, can be estimated by multiplying these ratios by the ⁴⁰K conversion factor.