Semi-insulating GaAs detectors degraded by 8 MeV electrons up to 1500 kGy

Radiation degradation of semi-insulating GaAs detectors by 8 MeV electrons up to doses of 1500 kGy is studied in this paper. The influence of irradiation on GaAs material parameters and on spectrometric and electrical properties of fabricated detectors is evaluated. The detector material was degraded before contact preparation, which ensured separation of radiation degradation solely to the bulk material, excluding the contact degradation. The positron annihilation lifetime spectroscopy (PALS) was involved to characterize the substrate material together with galvanometric measurements. Radiation-induced mono-vacancies were clearly identified by PALS in the irradiated materials with increasing concentration up to 2.8 × 1016 cm−3 at maximal applied dose. In correlation with defect concentration the electron Hall mobility decreased with dose down to 3270 cm2 V−1 s−1 and resistivity increased up to 5.22 × 108 Ω cm at 1500 kGy. The bulk material properties influenced the parameters of fabricated detectors. The detectors lost their current blocking behaviour at 1000 kGy according to current-voltage measurements. The charge collection efficiency during alpha-particle and gamma ray measurements almost exponentially decreased with applied dose from initial 40% down to 5% at 1500 kGy in the case of alpha spectrometry and from 48% to 12% at 500 kGy for gamma spectrometry.

GC investigation of post-irradiation oxidation phenomena on polypropylene

The paper summarizes the results of research on gas products of polypropylene (PP) radiolysis. Particular attention was paid to the phenomena of post-radiation degradation of PP. The protective effect of selected aromatic compounds was investigated. The research was carried out both from the point of view of obtaining radiation-resistant PP varieties and the possibility of accelerating biodegradation phenomena, e.g., PP/cellulose composition. The phenomena of post-radiation chain oxidation of PP were investigated by gas chromatography (GC). The GC in the system used (packed column, thermal conductivity detector, argon – carrier gas) enables the determination of H2, O2, CO, and CH4 in one measurement. The samples were irradiated with electron beams (EBs) accelerated in accelerators: Elektronika 10/10 with a power of 10 kW and energy of 10 MeV and LAE 13/9 with a power of 9 kW and energy up to 13 MeV. In the tests, PP without stabilizing additives (obtained directly from the production line) and non-stabilized styrene were used. Radiolytic efficiency of hydrogen evolution allowed us to estimate the number of originally formed free radicals. The maintenance of the secondary oxidation processes was the loss of oxygen and the formation of oxidation products (CO, CH4). Attention is paid to the protective effect of aromatic compounds (polystyrene (PS), polyethylene terephthalate (PET), anthracene, fluoranthene, acenaphthene, pyrene, naphthalene) both at the stage of hydrogen atom separation and the secondary oxidation process. The examples of post-radiation oxidation of PP irradiated in cryogenic conditions (–196°C) are presented. All used aromatic compounds showed a protective effect in PP radiolysis. We suppose that this phenomenon is responsible for the charge transfer along the polymer chain from the ionization spurs to the aromatic compound. The protective ranges of PS in PP radiolysis were estimated for the variously prepared PP/PS type compositions from 6 mers to 28 mers.

Prediction of radiation degradation of Si detectors irradiated by relativistic ions of different masses

The presented paper is focused around radiation damage of silicon material under the different ions irradiation. The ion total energy range is 0.7 GeV for 7Li to 208 GeV for 208Pb. The results of TRIM modeling for the set of six ions are presented. The extracted information about vacancy production allows making first assumptions of the Si degradation dependence on mass and energy of the incident ion.

Impact of electron beam irradiation in potato starch films containing hibiscus aquous extract

The development of starch films containing natural antioxidants is one alternative of active packaging. Starch is a well-studied natural biopolymer that can be used for the development of biodegradable films because it presents a low cost, is easy to obtain and presents good ability to form films. Hibiscus sabdariffa, commonly known as hibiscus, roselle or red sorrel, is an annual herbaceous sub shrub that contains many types of biocompounds, including organic and phenolic acids. The aim of the present work was to determine the influence of electron beam irradiation on potato starch film containing hibiscus extract. The aqueous hibiscus solution was prepared by boiling for 3 min 1% w/ml dehydrated hibiscus flowers in 500 ml deionized water. The film forming solution was prepared by casting (5% potato starch, 3% glycerol as plasticizer and the hibiscus solution) and irradiated in a 1.5 MeV electron beam accelerator Dynamitron II (Radiation Dynamics Inc.), with doses of 0, 20, 40 and 60 kGy. After drying some mechanical properties were measured. The tensile strength of the control films and the irradiated ones was established. There were no significant differences among them. It looks like hibiscus antioxidants were able to prevent the expected starch radiation degradation process caused by radiation generated free radicals.