The Gamma and Neutron Sensor System for Rapid Dose Rate Mapping in the CLEANDEM Project.

The decommissioning of nuclear installations, as well as the possible necessary accident remediations, requires the physical presence of human operators in potentially radiologically hostile environments. The number of active nuclear reactors worldwide is greater than 400, and most of them are 40 to 50 years old, thus implying that soon they will have to be dismantled. In the framework of the H2020 CLEANDEM project, a small robotic vehicle is being developed that is equipped with a series of different sensors for areas that are significantly contaminated by radiation. In this work, we describe the MiniRadMeter system, a compact low-cost sensor capable of being used to perform quick gamma and neutron radiation field mapping of environments prior to the possible start of human operations. The miniature gamma sensor is a 1 cm3 scintillator counter with moderate spectroscopic features read out by means of a 6 × 6 mm2 SiPM, whereas neutrons are detected by means of a silicon diode coupled to a layer of 6LiF and placed inside a 6 × 6 × 6 cm3 polyethylene box. The front-end and data acquisition electronics were developed based on a Raspberry Pi4 microcomputer. In this paper, the system performance and the preliminary test results are described.

Exposure to metal nanoparticles changes zeta potentials of Rhodococcus cells.

Nanoparticles (NPs) of transition metals and their oxides are widely used in industries and exhibit diverse biological activities - from antimicrobial to growth promoting and regulating biofilms. In this study, the concentration-dependent effects of negatively charged metal and metal oxide NPs on the viability and net surface charge of Rhodococcus cells were revealed. Our hypothesis that zeta potential values of bacterial cells approach the zeta potential of NPs with an increase in the concentration of nanoparticles was statistically validated, thus suggesting the accumulation of nanoparticles on the cell surface. Thus, based on the dynamics of zeta potential, it would be possible to predict the accumulation of metal NPs on the cell surface of particular Rhodococcus species. It seemed that more toxic nanometals (e.g. CuO) accumulate more intensively on the bacterial cell wall than less toxic nanometals (Bi, Ni and Co). Physical properties of NPs, such as shape, size, dispersity and zeta potential, were characterized at different nanoparticle concentrations, in order to explain their diverse effects on bacterial viability, cellular charge and adhesion to hydrocarbons. Interestingly, an increase in Rhodococcus adhesion to n-hexadecane was observed in the presence of Cu and CuO NPs, while treatment with Fe3O4 NPs resulted in a decrease in the adhesive activity. The obtained data help to clarify the mechanisms of nano-bio interaction and make it possible to select metal and metal oxide nanoparticles to modify the surface of bacterial cells without toxic effects.