Research on minimum detectable activity (MDA) of underwater gamma spectrometer for radioactivity measurement in the marine environment.

To improve the capability of underwater gamma spectrometer to quantify radiation levels slightly above the background radiation in the seawater, the minimum detection activity (MDA) and factors including the background count, detection efficiency and acquisition time were studied using Monte Carlo simulation and field experiments. The simulation results show that the crystal type selected in the spectrometer and its volume, enclosure materials of the spectrometer and its thickness all affect the marine detection efficiency in in-situ measurement, and thus determine MDA of the underwater gamma spectrometer. The acquisition time and the placement depth of the spectrometer in the seawater also affect the MDA in the in-situ measurement. Some research data and suggestions on design and use of underwater gamma spectrometer were presented, which are of guiding significance for the in-situ radioactivity measurement in the marine environment.