In order to use a thermoluminescence dosimeter for personal monitoring, some practical characteristics such as reproducibility, deviation among elements, degradation of sensitivity were examined during the repeated usage over one year. It was shown that the correction of the reading to compensate for the deviation in sensitivities by the factor determined for each element is necessary. The elements mostly showed the degradation of sensitivity during the usage. The degradation was supposed to be caused essentially by the repeated annealing. The values by thermoluminescence dosimeter agreed fairly well with those by film badge in the wide range of energies higher than several 10 keV.
The collection efficiency of nine types of filter papers for air sampling was determined for monodispersed polystyrene latex aerosols by using a forward light scattering photometer. The aerosols were 0.091, 0.198, 0.365, 0.500 and 1.099μm in diameter, which flowed through a test filter paper at a face velocity from 4.2 to 200cm/sec. Toyo No. 660, No. 60 and No. LP filter papers exhibited minimum efficiencies at the face velocity range between 10 and 80cm/sec, and in the particle size range between 0.1 to 0.5μm. The collection efficiencies of Toyo No. 5A and Whatman No. 41 filter papers were over 95% for all the particle sizes at a face velocity higher than 100cm/sec. Toyo HE-40, HV-70, Toyo GB-100 and Gelman. E filter papers showed the collection efficiencies as high as more than 99%. The theoretical filter efficiency based on single fiber filtering mechanisms and the effect of neighboring fiber interference on the collection efficiency are also discussed.
Methods to determine the uranium isotopic ratio 235U/238U by neutron activation analysis were examined. Uranium isotopic ratio in several environmental samples containing small amount of uranium was determined by these methods. After isolated uranium samples were irradiated with thermal neutron flux at 3.5×1012n/cm2·sec for one hour, the radioactivity of 99Mo+99mTc produced from 235U fission and that of 239Np induced from 238U were measured by the following two methods to determine the isotopic ratio 235U/238U. 1. Energy spectrum analysis of γ-rays with a Ge (Li) semi-conductor detector. 2. Measurement of the radioactivity with a 2π gas-flow counter and a NaI (T1) scintillation counter after radiochemical isolation by solvent extraction. Comparing above two methods, it was found that β-counting using 2π gas-flow counter and γ-spectrometry gave preferable results with fluctuation below 5% to γ-counting using NaI (T1) scintillation counter. The isotopic ratios 235U/238U in environmental soil samples collected at Ningyo pass and its neighboring places in Okayama Prefecture and at Muro in Nara Prefecture were found to be in the range of 0.0062-0.0075, whereas the ratio in uranyl nitrate hexahydrate (commercial reagent) was 0.0076±0.0004.
An experimental method for calibrating a chamber used for 85Kr monitoring is described. Experiments were made with a cylindrical ionization chamber, 114mm in diameter, 150mm in height with walls of stainless steel, by using 85Kr gaseous sources. In order to standardize a 85Kr gaseous source used for the experiments, the activity of 85Kr in the gas was determined by the method of mass spectrometry. The standardized gas was diluted with air to obtain the suitable concentration of 85Kr for the calibration. In the calibration, the relation between activities of 85Kr in the chamber and saturated ionization currents was studied with the gases of various concentrations of 85Kr. The calibration factor of the chamber was found to be 5.42×10-9A/(μCi/cm3).
The Questionaire inquiry was carried out on the use of personnel monitors for external radiations in Japan. 400 institutions (including 71 universities, 9 electric power plants, 3 nuclear fuel companies, 13 non-destructive inspection companies, 58 industrial institutes, 36 national and public institutes, 94 hospitals, 29 pharmaceutical facilities, and others) were selected to send the questionaires, and 179 (45%) were answered and returned. Approximately 70% of the establishments replying had less than 50 employees. Film badges (FB) were used in about 90% institutions as a personnel dosimeter, TLD's in 13% and fluoro-glass dosimeters (FGD) in 6%. About 20% indicated the possibility of using FGD for personnel monitors in the future in lieu of FB, while 45% suggested TLD. The users' requests for the improvement of monitors were; (1) measurement of lower dose level (54%), (2) less expensive monitors (48%), (3) higher accuracy for low energy X, γ (37%), (4) monitors for detecting spot exposure (32%), (5) more uniform quality (30%), (6) higher accuracy for β-dose evaluation (30%), (7) improvement of reproducibility (29%), (8) improvement of mechanical strength (20%), (9) higher accuracy for neutron dose evaluation (12%), (10) higher accuracy for high energy X, γ (8%).