Description
Authors (affiliation): 1. Marcello Lunardon (Dept. of Physics and Astronomy, Padova University, Italy), 2. Paolo Sartori (Dept. of Physics and Astronomy, Padova University, Italy), 3. Luca Stevanato (Dept. of Physics and Astronomy, Padova University, Italy), 4. Pierino De Felice (ENEA-INMRI, Casaccia R.C., Rome, Italy)
We present 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.
This research is the follow-up of the EU-funded project TAWARA_RTM (FP7-SEC-2012-1, grant no. 312713), closed several years ago, where a high sensitivity monitoring system for radioactivity in water intended for human consumption was realized. Despite its notable results in terms of sensitivity and overall features for water radioactivity monitoring, which make it still a state-of-the-art instrument in this context, the characterization campaign showed several aspects that could be improved, the main one being the effects of surface contamination of the radiation detectors, in terms of both deterioration of the sensitivity and possibility to efficiently clean-up the system to recover the original performance.
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 protective window. 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 technical limitation for 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 detection performance for alpha and beta particles was first tested in air with standard sources, showing results very similar to commercially available detectors. Later a number of tests were carried out in the ENEA-INMRI laboratories to characterize the contamination and decontamination properties. Initial activity was checked by low background radioactivity measurements, then the detectors were immersed 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 carried out on small size samples, several large area detectors were realized and used to build a small concept 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.
