Evaluation of Differences in Response of DOD Portable Instruments and Solid-State Detectors used by MEXT for Measurement of External Radiations with Attention to the Cosmic Radiation Component

摘要

This report discusses cosmic radiation and summarizes its contributions to radiation dose from external sources and the implications on measurement of external dose-rate using either pressurized ion chambers (PICs) or thallium-activated sodium iodide NaI(Tl). The report finds that some NaI(Tl) systems under respond to cosmic radiation above 3 MeV deposited energy. These differences are offered as one of several contributors to the lower values of external dose rates measured by Japan s Ministry of Education, Culture, Sports, Science, and Technology (MEXT) using NaI(Tl) compared to DOD/DOE measurements using PICs. The report concludes that such limitations must be accounted for in performing assessments of dose from external sources.