Analysis of the ambient dose variation due to cosmic rays in Daejeon by using a neutron monitor

Abstract

The Basic Atomic Energy Research Institute of Hanyang University in Korea has constructed a cosmic-ray detection system that is presently being operated. In this study, the impact of cosmic-rays on 18-tube NM64-type neutron monitor installed in Daejeon was confirmed for the first time. In order to evaluate the reliability of the neutron monitor, we predicted the count rates from the neutron flux by using the Excel-based Program for calculating Atmospheric Cosmic-ray Spectrum (EXPACS); these predictions were then compared with experimental results. The predictions agree well with the results, with differences no greater than 3.95%. Also, changes in the neutron ambient dose equivalent rate from cosmic rays due to different environmental conditions were analyzed using EXPACS; the results obtained were compared with those of previous studies and were thus, confirmed to be reliable, suggesting that the detection system is suitable for making the relevant measurements. That detection system was then used to evaluate the neutron ambient dose equivalent rate for various environmental conditions in Daejeon. Finally, a conversion coefficient, defined as the ratio of counts from the neutron monitor to the neutron ambient dose equivalent, was obtained and included considerations of the impacts of geological factors and of meteorological factors of relative humidity and atmospheric depth. The derived formula fit the source data with an adjusted coefficient of determination (R2) of 0.9894 and a root-mean-square error of 1.7056 × 10−10, equivalent to about 1%. This confirmed satisfactory accuracy and reliability of the formula, thereby showing this methodology to be legitimate for use in evaluating the neutron ambient dose equivalent by using the Daejeon neutron monitor.