The spreading use of organic insulating materials in environments such as space and nuclear power stations is increases the concern about the reliability of electrical insulation in these environments due to radiation and atmospheric pressure effects on the surface breakdown of polymers. This paper describes the effects of atmospheric pressure and gamma-ray irradiation on the discharge characteristics. The experiment was carried out by do impulse voltage under decreased pressure. Polybutylene terephthalate which was irradiated in air up to 100 kGy and 1 MGy with dose rate of 10 kGy/h using a60Co gamma-source has been used as the test sample. The total dose of gamma-ray irradiation effects on the discharge quantity have been studied. The changes of discharge quantity is discussed with decreasing the atmospheric pressure in the range from 100 kPa to 1 kPa and the frequency of applied impulse voltage in the range from 100 Hz to 250 Hz. The discharge quantity increased with increasing the total dose of gamma-ray irradiation, and decreased with decreasing the atmospheric pressure. The discharge quantity increased with increasing the frequency of applied impulse voltage.
It is necessary to evaluate combined effects of ionizing radiation and other toxic agents on ecosystems, because ecosystems are exposed to these various factors. The authors studied combined effects of γ-rays and acidification on an experimental model ecosystem (microcosm) mimicking aquatic microbial communities. Microcosms, consisted of flagellate algae Euglena gracilis Z as a producer, ciliate protozoa Tetrahymena thermophila B as a consumer and bacteria Escherichia coli DH5α as a decomposer, were loaded by the following treatments : (1) Irradiation with 100 Gy 60Co γ-rays ; (2) Acidification of culture medium to pH 4.0 with the mixture of 0.1 N HNO3and 0.1 N H2SO4 (1: 1, v/v), which mimicked acid rain; and (3) Irradiation with 100 Gy γ-rays followed by the acidification of the culture medium (pH 4.0) . The γ-irradiation induced a temporary decrease in cell densities of E. coh, but did not affect cell densities of the other species. The concentrations of chlorophyll a and ATP in the microcosm were not affected by the γ-irradiation, and chlorophyll a concentrations in a Eu. gracilis cell were not affected, either. The acidification significantly decreased cell densities of T. thermophila, slightly decreased cell densities of E. coli, and slightly increased cell densities of Eu. gracilis. The concentrations of chlorophyll a and ATP in the microcosm were increased by the acidification, although chlorophyll a concentrations in a Eu. gracilis cell were decreased The combined exposure to γ-rays and acids temporarily decreased cell densities of E. coli, significantly decreased cell densities of T. thermophila, and slightly increased cell densities of Eu. gracilis. The concentrations of chlorophyll a and ATP in the microcosm were increased by the combined exposure, although chlorophyll a concentrations in a Eu. gracilis cell were decreased The authors therefore conclude that combined exposure to γ-rays and acids had additive effects on cell densities, chlorophyll a and ATP concentrations in the microcosm, and chlorophyll a concentrations in a Eu. gracilis cell.
For the practical use of radicidation, we studied on the effects of γ-ray and electron beam on functional properties of beet red colorant, natural colors with low heat stability and high possibility of microbe contamination. Neither γ-ray or electron beam had any significant influence on color contents and color tone of red beet products at less than 10 kGy of irradiation for the practical use. Influence of moisture content at level of less than 20% in powdered product was not observed. The results suggest that both γ-ray and electron beam irradiation is significantly effective in decontamination of powdered beet red products.