Nobuyuki Kinouchi

Simulation of the Background for Gamma Detection System in the Indoor Environments of Concrete Buildings

The indoor background has significance in determining the minimum detectable level of gamma detection systems. The gamma radiation field in a concrete building was studied by using the Monte Carlo simulations. The parameters of wall thickness, room shape and dimensions were considered in the modeling. A spherical layer model was assumed as the indoor source geometry with the intention of easy and effective calculations. The simulation model was applied to an unshielded germanium detector and the detection system with a more complex shielding configuration. As the results, the indoor radiation field in the concrete building can be predicted well by assuming the source geometry of a spherical concrete layer with a real thickness and the homogeneously distributed source of the natural major three components, the 238U series, 232Th series and 40K. The simulation model is useful for designing and optimizing gamma detection systems or shielding assemblies.

Design of an anti-Compton spectrometer for low-level radioactive wastes using Monte Carlo techniques

An anti-Compton spectrometer with semi-2π Compton suppression is designed to identify the photons emitted from low-level radioactive wastes from radioisotope usage and nuclear research laboratory. Since the objective sample is massive and large, the system has a full opening toward the sample position. The characteristics and features of the system concerning Compton suppression and reduction of the background component due to natural radioactive source are estimated by the Monte Carlo simulations. The anti-Compton technique is shown to be quite advantageous for the reduction of the surrounding natural background radiation, as well as the suppression of the background for the higher energy photons.

Development of a Plutonium Air Monitor for Emergency Environmental Monitoring.

We have developed an air monitor which is possible to measure rapidly and sensitively the concentration of plutonium for the environmental monitoring at an accident of a nuclear reprocessing plant. The monitor is designed to collect airborne plutonium by drawing the ambient air through a filter and to detect the activity by alpha spectroscopy. The following two methods are equipped with the monitor: continuous measuremeat at atmospheric pressure and batch measurement at vacuum. The description of the air monitor and the results of performance test are reported.

A Simple Method Evaluating Collection Performance of Air Filters with Imaging Plates.

Collection performance such as collection efficiency and surface collection efficiency is considerably important in order to select a suitable filter for the measurement of the concentrations of airborne radioactive particles. A simple method with imaging plates is proposed to evaluate the collection performance of air filters. By comparing the collection performance of some filters with natural airborne radioactivity as a test aerosol, it was confirmed that the method could reliably evaluate the collection performance of filters.

Uniformity of Beta-ray Plane Sources for the Calibration of Surface Contamination Monitors.

Uniformity of different types of beta-ray plane sources has been examined. Four types of plane sources, polymer, anodized aluminum, filter and ion exchange membrane, were selected. On estimation of the uniformity, the coefficient of variation with respect to surface emission rate was measured using an imaging plate or a proportional counter. As a result, polymer sources and ion exchange membrane sources showed good uniformity. The area and number of region of interest for estimation of uniformity were discussed.