Rainfall Investigation by Means of Marine In Situ Gamma-ray Spectrometry in Ligurian Sea, Mediterranean Sea, Italy

Marine in situ gamma-ray spectrometry was utilized for a rainfall study at the W1M3A observing system in Ligurian Sea, Mediterranean Sea, Italy. From 7 June to 10 October 2016, underwater total gamma-ray counting rate (TCR) and the activity concentration of radon daughters 214Pb, 214Bi and potassium 40K were continuously monitored along with ambient noise and meteorological parameters. TCR was proven as a good rainfall indicator as radon daughters’ fallout resulted in increased levels of marine radioactivity during and 2–3 h after the rainfall events. Cloud origin significantly affects TCR and radon progenies variations, as aerial mass trajectories, which extend upon terrestrial areas, result in higher increments. TCR and radon progenies concentrations revealed an increasing non-linear trend with rainfall height and intensity. 40K was proven to be an additional radio-tracer as its dilution was associated with rainfall height. 40K variations combined with 214Bi measurements can be used to investigate the mixing of rain- and seawater. In comparison with measurements in the atmosphere, the application of marine in situ gamma-ray spectrometry for precipitation investigation provided important advantages: allows quantitative measurement of the radionuclides; 40K can be used, along with radon daughters, as a radio-tracer; the mixing of rain- and seawater can be associated with meteorological parameters.

Response Function Test of Marine γ-Spectrometry with Different Detector Material

The marine radioactivity measurement is the low-level radiation measurement, whose accuracy mainly depends on the material and design of the detector. However, the currently research results mainly focus on the qualitative research. In this paper, a Monte Carlo code MCNP was utilized to simulate the comparation of the energy spectra of several relevant γ rays recorded by detectors immersed in seawater, The detection efficiency and the effective detection distance of these detectors to the radionuclides of 137Cs dispersed in seawater were calculated．The results of our experiment shown that the effective detection distance of these detctors to γ radionuclides depends on the detector material and γ-ray energy. The LaBr detector has the best price performance ratio, however, considering the balance between the low-cost and highly detection efficiency, the NaI detector is also a better choice.