We present the results of a series of radioactivity contamination tests on a novel contamination-safe scintillation detector to be used for alpha and beta radiation detection in water. 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 intended for human consumption, this kind of detectors must have large area, very low intrinsic background and avoid, possibly, any kind of window between the monitored water and the detector active volume. When water is in direct contact with the detector surface even an extremely low contamination can therefore destroy the 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 with functionalized surface, developed and produced by our research group 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.
A number of tests were carried out at the ENEA-INMRI laboratories with the aim to characterize the contamination and decontamination properties of the newly developed detector. Basically the initial activity of each detector foil was checked by low background radioactivity measurements. Further, detectors were immersed for fixed times and constant procedure in a variety of radioactive reference liquid solutions with different radionuclides in different chemical forms. To this purpose an automatic devise for controlling the immersion cycle was developed and used. After rinsing with distilled water the detector foils were again measured for residual radioactivity adsorbed on the foils surface.
Radioactivity measurements were based on HPGe gamma spectrometry and low-background alpha/beta counters. Characteristic limits were determined following the ISO-11929 standard.
Results are presented and discussed with reference to the various detector and functionalized surfaces developed.