New measurement techniques of environmental radioactivity. Methods of surveying marine radioactivity

Measurements of radioactivity have been carried out in solution or suspension in sea-water, bottom sediments and specific marine organisms. The general approach to radionuclide measurement in seawater and bottom sediments has been concentration by coprecipitation, adsorption, ion exchange or solvent extraction. These methods employed are based primarily on shipboard collection of samples followed by land-based laboratory analyses and are too time-consuming. For rapid measurement, in situ measurement of seawater or seabed gamma-ray has developed. A gamma-ray detecting probe containing the NaI(Tl) scintillation or germanium detector is enclosed in a sealed cylinder. The measurements are made by suspending the probe in a 200-300 liter tank and passing seawater through the tank by means of ship deck pumping system, towing the probe across the seafloor, hanging down the probe to the seabed, or loading the probe on a remotely operated undersea vehicle. In situ measurement of gamma-ray in the marine environment has some application to a mineral exploration and to monitoring of sea areas which may become contaminated as the result of accidents or contamination incidents. This article reviews several gamma-ray detecting probes and describes the recent studies at JAERI on the development of a small electric-cooled Ge gamma-ray detector and a marine environmental radioactivity investigation system for in situ measurement of gamma-ray. (J.P.N.)