Very soon after the introduction of the application of thermoluminescene (TL) for dosimetric purposes the method was used also for environmental monitoring.Thermoluminescence dosimetry (TLD) systems are permanently developed and improved.The aim of the present paper is to help the reader to introduce TLD for environmental monitoring. Therefore the paper describes the brief theoretical background of thermoluminescence. The elements of TLD systems, such as detectors, readers and measurement cycle including annealing, package and storage, irradiation, readout and mathematical evaluation are summarised. The main characteristics of various TL systems (batch homogeneity, sensitivity, reproducibility, linearity, light sensitivity, fading and energy dependence) are analysed mostly from the viewpoint of use in environmental monitoring. Special attention is given to the performance test requirements of the International Electrotechnical Committee and the importance of intercomparisons. Some environmental dosimetry applications during the last ten years are also reviewed.
An access-control system has been developed for the safety operation of the large helical device (LHD) at the National Institute for Fusion Science.The central part of the control system consists of a main computer, a manual-operation box and a sequencer-control system. The system monitors five turnstiles, eight shielding doors and other points of entry and directly supplies the interlock signals to the LHD control system. The sequencer-control system, which provides independent access control of each gate, is effective to control simultaneously all of the entry according to the status of the LHD and to permit the access of radiation workers belonging to a specific work group according to the situation of LHD plasma experiment. The safety management of LHD experiments has been performed without any serious troubles by this access control system including the interlock system since 1998.
Effects of the weak leakage magnetic field are studied on the response of two kinds of scintillation survey meters: an ordinary type for γ-rays and that optimized for the detection of low-energy photons from 125I.In the presence of the magnetic field, the response of the optimized survey meter decreases to the photons from 125I, and increases considerably to the background radiations. On the other hand, the response of the ordinary survey meter decreases slightly to both the γ-rays from 131I and the background radiations.From analysis of the pulse-height spectra for the radiations, such variations of the response are ascribed to the reduction of the amplification factor of photomultiplier tubes by the magnetic field.
A new method has been proposed for calculating the dose rate around a radioisotope reservoir tank using EGS4 (Electron Gamma Shower Version4). Several improvements, such as uniform distribution of the radioactive substances in the reservoir tank and shielding effect by the tank wall, were made for more accurate determination of the activity-todose rate conversion coefficients. The Monte Carlo code EGS4 was employed in this report, and the cumulative dose around the reservoir tank was calculated. The results of calculations are useful for a design for radiation safety management in PET (positron emission tomography) facilities.
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