By means of the annular collimator camera, we newly proposed an inspection technique to identify the source origins of leaked X-rays. In order to demonstrate the availability of our technique, an experiment using the test model of an X-ray inspection apparatus was presented. In this experiment, a leak point at the collimator of an incident X-ray could be identified. Because this leak point was located in the inside of the equipment, it was difficult to apply a conventional testing method using handy-type radiation detectors. We concluded that our method was valuable for implementers to create safer inspection systems.
1–cm dose equivalent rates at the surface of blocks made of ordinary concrete, iron, stainless steel and aluminum, which were irradiated by secondary particles produced by 30–MeV protons, and 10–MeV, 30–MeV and 1 to 10 GeV electrons, were calculated by the EGS4 code. The results showed that the induced radioactivity of the “clearance concentration” can be easily detected by an NaI(Tl) scintillation survey meter. Conversion factors of surface dose rate to radioactivity were also calculated.
In the Japan Atomic Energy Agency (JAEA), exposures doses to fingertips can be significant in radiological decontamination at the facilities with mixture fields of beta and gamma (X) rays. The radiation doses to fingertips have been measured by ring type dosemeters equipped with thermoluminescence dosemeters (TLD) in JAEA. We applied small Optically Stimulated Luminescence (OSL) elements to the ring type dosemeter, which has the advantages in the use for long term and repeating in dose measurements comparing to the TLDs. The dose evaluation method with the new ring type dosemeters was established with studies on the characteristic of the OSL dosemeters by irradiation examinations and Monte Carlo simulations. In this report, we introduce the outline and the dose evaluation method of the new ring type dosemeter which we applied.
From October to December 2010, just before the radiological accident at the Tokyo Electric Power Company Fukushima Daiichi nuclear power plant, 71 radiation professionals belonging to the radiation facilities in Japan were asked what they consider as a “safe” dose of radiation for themselves, their spouse, parents, children, brothers and friends. Although the “safe” dose varied widely from less than 1 mSv/y to higher than 100 mSv/y, the average dose was 35.6 mSv/y that was around the middle point between the exposure dose limits for annual average (20 mSv/y) and for any single year (50 mSv/y). Similar results were obtained from another surveys for the members of Japan Radioisotope Association (36.9 mSv/y) and for the Oita Prefectural Hospital (36.8 mSv/y). Among the family members and friends, the minimum average “safe” dose was 8.5 mSv/y for children, to whom 50% of responders claimed the “safe” dose less than 1 mSv. Gender, age and specialty of the responder also affected the “safe” dose. These findings suggest that the perception of radiation risk varies widely and that the legal exposure dose limit derived from the regulatory science may act as an anchor of safety even in radiation professionals. The different level of risk perception for different target groups in radiation professionals appears similar to those in non-professional whole population. The gap between these characteristics of real radiation professionals and the generally accepted picture of radiation professionals might take a part in a state of confusion after the radiological accident.
Pollutant on the leaves and pinecones of Pinus thunbergii contaminated by radiocesium in Fukushima City were measured, the safe use of the leaves and pinecones as children's toys and craft materials was prospected after the accident at the TEPCO's Fukushima Daiichi nuclear power plant. The radiocesium concentration on Pinus thunbergii leaves on February 22, 2013 was 1/5.7 of the concentration on May 2, 2012. The radiocesium concentration on pinecones was high (16,300 Bq/kg). Radiocesium attached to the latex glove worn when collecting polluted pinecones, and this level fell by 1/5.2 when the polluted glove was washed. Negligible amount of radiocesium was detected in the used glove for collecting of dirty pinecones after painting. It is reasonable to assume that the use of pinecones as craft materials will be possible in the near future because the radiocesium concentration levels are expected to decrease after 2014.
Sumida and Ohta wards in Tokyo and Shobara City in Hiroshima are approximately 220 km, 238 km and 775 km away from the Fukushima Daiichi Nuclear Power Plant (FDNPP), respectively. Drinking water (DW) samples were obtained from the taps at these three locations during the period from late March 2011 until early March 2013. The concentrations of the 131I, 134Cs and 137Cs activities in the DW samples have been measured. The radioactive cesium (Cs) concentration at Sumida ward had decreased until the end of 2011, and showed a repeated trend of increase and decrease afterward. During the early period after the Great East Japan Earthquake, the 131I concentration had more acutely decreased at Sumida ward. On 3 April 2011, the 131I concentrations in the DW samples at Sumida and Ohta wards agreed with each other within uncertainty. The radioactive Cs concentration at Ohta ward has tended to be less than that at Sumida ward during the two-year period. In Shobara, the 131I concentration in a DW sample on 7 April 2011 was possibly greater than 0.01 Bq/kg. This implies that the 131I activities included in air dusts and rain might have entered into the river water in Shobara in early April 2011. The radioactive Cs concentrations in the six DW samples at Shobara City during the period from 24 March 2011 to3 March 2013 were regarded as zero within uncertainty ranging from 0.001 Bq/kg to 0.007 Bq/kg.