Kelp contains naturally occurring radioisotopes. Edible kelp flakes were used to fabricate a disk-shaped radiation source by a method involving compression and formation. This method is suitable for fabricating kelp radiation sources and does not require any special skills or techniques. The kelp radiation sources were used in an educational course on radiation and their suitability for use in the classroom was assessed by performing two tests on the dependence of the radiation count rate on distance and shielding. The distance dependence test demonstrated that the relationship between distance and radiation count rate could be explained by the inverse-square law, while the shielding dependence test showed that the shielding effectiveness increased with mass density and that the radiation count rate decreased exponentially with shielding thickness. It was concluded that the compression and formation method was suitable for fabricating kelp radiation sources that are effective educational tools for illustrating the existence of naturally occurring radioisotopes and demonstrating the principles of radiation protection.

抄録全体を表示

  New-type radiophotoluminescence (RPL) glass dosimeters, which had thin sensitive layers near their surface, were made for the examination of their response to low energy (15-25 keV) X-rays necessary for mammography. We constructed a laser scanning microscope system for the effective measurement of RPL photons from an X-ray irradiated glass dosimeter. The X-ray sensitive region of the new-type glass dosimeter was near its surface, and moreover a thin X-ray absorption glass filter, whose photon attenuation coefficient was almost the same as the glass dosimeter, was put on the new-type glass dosimeter. These new-type glass dosimeters were irradiated with low energy X-rays and measured results of absorbed dose around their surface layers agreed on the whole with results from photon transport calculations. It was confirmed that RPL glass dosimeters could make a reliable service to the low energy X-ray dosimetry for mammography.

抄録全体を表示

  A flexible hose made of plasticized polyvinyl chloride was introduced into underground radioactive wastewater drainpipes as preventative maintenance. We completed a seamless connection spanning the longest interval between the last confluence point and the wastewater tank. Although the flexible hose is not a construction material but rather a consumable article, it is robust against the effects of temperature change and erosion by chemical substances. Moreover, it is placed in an underground steel pipe where it is protected from UV irradiation and friction. Therefore, increased hose durability is expected. In addition, the risk of damage from earthquakes or ground subsidence is negligible due to the flexibility of the hose. Compared with a full renovation of the plumbing, the economic cost is much cheaper and the construction period is much shorter. We propose the use of flexible hoses as one of the most convenient methods to prevent leakage accidents at radioisotope facilities with underground plumbing for wastewater.

抄録全体を表示

  Precise ¹⁵²Eu gamma-ray measurements in the granite samples exposed to the Hiroshima atomic bomb require concentrating the europium (Eu) and excluding natural radioisotopes. In this study, an ion exchange method was applied for isolating Eu ions from granite samples at 56 m, 502 m and 818 m distances from the hypocenter. Although the Eu samples included ²³²Th atoms, the ¹⁵²Eu 344 keV gamma-ray full energy peaks were scarcely affected by the gamma rays from the radioisotopes of the thorium series. Almost all of the radioisotopes in the uranium and actinium series were removed. The Eu contents were determined by atomic absorption spectrometry. The ¹⁵²Eu specific radioactivities in the samples at 56 m and 502 m were higher than those inferred from the DS02 calculations. In the sample at 818 m, the measured value was in agreement with the calculated value based on the DS02. Estimations of the atomic bomb radiation doses are necessary for many investigations which attempt to decide the acceptable levels of radiation risk to the public and workers. The results in the present study will be useful for studying the uncertainties of the estimated atomic bomb radiation doses.

抄録全体を表示