The tritium survey meter consisting of gass flow counter with a large area thin window is developed. The large window (30mm×150mm) with extremely thin film made of alkyl benzene polymer (0.15mg/cm2) is installed at the counter. Argon including 10% methane was used for counting gas. A tritium check source was prepared to examine the characteristics of the survey meter. The source was made of a multi-layer film of [9, 10-3H] stearic acid on a metal plate. This film is thin enough to neglect the self-absorption of β-rays. Plateau characteristics and detection efficiency of the tritium survey meter are described. The sensitivity of this survey meter can be evaluated less than 1/20 of the maximum permissible surface contamination with tritium (10-3μCi/cm2) in Japan.
Concentration of NaCl aerosol released from a fume hood to the work place was measured at face velocities of fume hood up to 0.5m/sec. Influence on the release rate of aerosol was investigated, i. e. the movement of a worker in front of the fume hood and the flow rate of room air supply. Release of the aerosol was detected in work place when fume hood face velocity was lower than 0.4m/sec. The concentration of aerosol released to the work place increased with a decrease in the face velocity. On the other hand, the release was not detected at face velocity 0.5m/sec in any working condition, where the concentration in the air was less than 8×10-12μg/cm3 per dispersion rate (μg/min), as the detection limit. This value was 1/4, 000 of the concentration which was estimated assuming that 1/10 of the aerosol quantity in the fume hood was released.
This simple calibration equipment consists of two or more 137Cs line radiation sources having equal activities and a lead-shield vessel. The sources are placed symmetrically within the vessel. The purpose is to have uniform exposure rate in the center of vessel where a GM probe is inserted. Its features are efficient calibration and reduction of personal exposure for workers.
The surface dose rate of the vermiculite column was measured during about two years with TLD to predict the migration of 137Cs in the adsorbent layer. The vertical distribution of the surface dose rate was obtained from the data measured at intervals of five centimeter in vertical direction. From this dose rate distribution we estimated the length of the 137Cs adsorbed layer and calculated Kf value and distribution coefficient Kd of 137Cs using Inoue's method. And we calculated the surface dose rate of the vermiculite column considering the 137Cs adsorbed layer as a volume source of a uniform activity distribution. For this calculation, we simplified the shape of the vermiculite column to triple layer cylinder. The core of this cylinder is vermiculite which is surrounded with rubber and mild steel shells. Broder's equation is used to calculate a build-up factor for multi-layer materials. The result of this calculation shows good agreement with the measured values with TLD, thus we can estimate the migration of 137Cs in a vermiculite column by measuring the surface dose rate with TLD.
A graphite pile was constructed for routine calibration of radiation protection instruments. An isotropic thermal neutron irradiation field can be set up at the cavity in the pile. Also a collimated thermal neutron beam irradiation field can be set up at the outside facing the rectangular hole of pile. The sizes of irradiation fields are 200×276×170mm3 and 160×160mm2 respectively. Thermal neutron fluences are measured by the gold foil activation method. The over all error of fluence measurements is less than±2%. Intercomparison between ETL and JAERI on thermal neutron fluence rate measurements was done and the results have agreed within experimental errors. Distribution of fluence rate in the irradiation field are uniform with ±3%.
The number concentration and size distribution of aerosol particles are the most important factors determining their behaviour. The number concentration and the size distribution of particles were measured with a condensation nuclei counter (CNC) and a light scattering particle counter (PC) or an electrical aerosol size analyzer (EAA), respectively, under the various ventilation conditions. The measurements were done in the Kyoto University Reactor (KUR), the Kyoto University Critical Assembly (KUCA) and the Institute of Atomic Energy, Kyoto University (KUTAE). The particle number concentration in the room increased by ventilation air introduced from outside of the building. The size distribution in the room was very close to the Junge distribution having the mean diameter of 0.02-0.06μm. The particle number concentration was lowest in the KUCA whose ventilation system is a circulation mode.