Development of a prototype of monitor for alpha and beta radiation in water using new silicone-based contamination-safe detectors

Abstract

We present here the main results of an experimental activity aimed at the realization of a prototype of monitor for alpha and beta radioactivity in water exploiting a novel type of contamination-safe scintillation detector developed by our research group. Due to the short path-length of alpha and beta particles in water and the low detection limits needed to be compliant with the international legislations in matter of radiation safety for water, the detectors to be used for such a kind of instruments should have in general large area, very low intrinsic background and avoid any kind of window between the monitored water and the active volume of the detector. Even an extremely low contamination of the surface can therefore destroy the detector performance, while protecting the detector with a layer of passive material will reduce the detection efficiency, in particular for alpha particles, and the passive layer can get contaminated itself, making necessary its substitution and representing an important limitation to the realization of a radioactivity monitor that should work continuously for years. The novel detectors are large-area silicone-based scintillators developed and produced in our laboratories. The technology we propose is a significant step forward in the direction of the realization of radioactivity monitors for water with high sensitivity and reasonable costs, to be used to improve security and quality of the water distributed to European and worldwide citizens. The detection performance for alpha and beta particles was first tested in air with standard sources, showing results very close to similar detectors commercially available. Later a number of tests were carried out in the ENEA-INMRI laboratories with the aim to characterize the contamination and decontamination properties. Initial activity of each detector foil was checked by low background radioactivity measurements, then the detectors were immersed for fixed times and constant procedure in a variety of radioactive reference liquid solutions with different radionuclides in different chemical forms. After rinsing with distilled water the detector foils were again measured for residual radioactivity adsorbed on the foils surface. After this preliminary campaign of contamination measurements carried out on small size samples, several large area detectors were realized and used to build a small demonstrator device for continuous monitoring of the radioactivity in water. The monitor was tested with distilled water (blank) and radioactive aqueous solutions, demonstrating the possibility to realize a new generation of radiation monitors for water with high sensitivity and with the possibility to easily manage the contamination issues.