Radiation Hardness of 4H-SiC P-N Junction UV Photo-Detector

4H-SiC based p-n junction UV photo-detectors were irradiated with 600 keV He+ in the fluence range of 5 × 1011 ÷ 5 × 1014 ion/cm2 in order to investigate their radiation hardness. The effects of irradiation on the electro-optical performance were monitored in dark condition and in the UV (200 ÷ 400 nm) range, as well as in the visible region confirming the typical visible blindness of unirradiated and irradiated SiC photo-sensors. A decrease of UV optical responsivity occurred after irradiation and two fluence regimes were identified. At low fluence (<1013 ions/cm2), a considerable reduction of optical responsivity (of about 50%) was measured despite the absence of relevant dark current changes. The presence of irradiation induced point defects and then the reduction of photo-generated charge lifetime are responsible for a reduction of the charge collection efficiency and then of the relevant optical response reduction: point defects act as recombination centers for the photo-generated charges, which recombine during the drift/diffusion toward the electrodes. At higher irradiation fluence, the optical responsivity is strongly reduced due to the formation of complex defects. The threshold between low and high fluence is about 100 kGy, confirming the radiation hardness of SiC photo-sensors.

Increased Biting Rate and Decreased Wolbachia Density in Irradiated Aedes Mosquitoes

Background: Releasing considerable numbers of radiation-sterilized males is a promising strategy to suppress mosquito vectors. However, releases may also include small percentages of biting females which translate to large numbers when releases are large.Currently, the effects of irradiation on the host-seeking and host-biting behaviors have not been exhaustively investigated. Information is also lacking regarding the effects of sterilizing treatment on the endosymbiotic bacterium Wolbachia, which is known to affect the vector competence of infected mosquitos.Methods: To ascertain the effects of irradiation on females, the pupae of two Aedes albopictus strains, differing in their natural or artificial Wolbachia infection type, and Ae. aegypti—which is not infected by Wolbachia—were treated with various doses of X-rays and monitored for key fitness parameters and biting behavior over a period of two weeks. The effect of radiation on Wolbachia was investigated by qPCR and FISH analysis.Results: Partial Ae. albopictus female sterility was achieved at 28 Gy but the number of weekly bites more than doubled compared to that of the controls. Radiation doses of 35 and 45 Gy completely inhibited progeny production but did not significantly affect the survival or flight ability of Ae. albopictus females and caused a tripling of the number of bites per female per week (compared to untreated controls). These results were also confirmed in Ae. aegypti after treatment at 50 Gy. Wolbachia density decreased significantly in 45-Gray-irradiated females, with the greatest decreases in the early irradiation group (26±2-hour-old pupae). Wolbachia density also decreased as adults aged. This trend was confirmed in ovaries but not in extra-ovarian tissues. FISH analysis showed a strongly reduced Wolbachia-specific fluorescence in the ovaries of 13±1-day-old females.Conclusions: These results suggest that, under SIT programs, the vector capacity of a target population could increase with the frequency of the irradiated females co-released with the sterile males due to an increased biting rate. In the context of a successful suppression, the related safety issues could be generally negligible, but they should be conservatively evaluated when large scale programs relying on imperfect sexing and high overflooding release ratios are run for long time in areas endemic for arboviral diseases. Also, the effects of irradiation on the vector competence deserve further investigation.

Investigation of the Tribological Performances of Graphene and WS2 Nanosheets as Additives for Perfluoroalkylpolyethers Under Simulated Space Environment

The tribological performances of perfluoroalkylpolyethers (PFPE) with graphene (Gr), WS2, and the mixture of Gr and WS2 (Gr + WS2) before and after ultraviolet (UV), atomic oxygen (AO), and proton (Pr) irradiations were investigated. The composition and structure of PFPE, Gr, WS2, and Gr + WS2 were also analyzed to understand the effects of irradiation on the tribological behaviors of PFPE with additives. The results indicated that serious deterioration and degradation of PFPE took place and Gr was transformed to amorphous carbon after Pr irradiation, and surface oxidation of WS2 occurred under the irradiations of AO and Pr. Moreover, compared to PFPE and PFPE additized with Gr and WS2, PFPE with the addition of Gr + WS2 exhibited excellent friction and wear reduction before and after UV and AO irradiations. Graphical Abstract