Cosmic-ray Contribution in Measurement of Environmental Gamma-ray Dose

• Published in: RADIOISOTOPES 1996/11/15, Vol.45(11), pp.665-674
• Main Authors: NAGAOKA, Kazunori, HONDA, Kouichirou, MIYANO, Keiji
• Format: Article
• Language: eng ; jpn
• Subjects: air-equivalent ionization chamber; cosmic ray; environmental gamma ray; NaI (Tl) scintillation spectrometer; pressurized ionization chamber; self-dose; thermoluminescence dosimeter
• ISSN: 0033-8303; 1884-4111
• DOI: 10.3769/radioisotopes.45.11_665

Nowadays several kinds of dosimeters are being used for environmental gamma-ray monitoring. However the results measured by those instruments are not always in good agreement. It may be caused from the different characteristics of dosimeters. In particular the different responses of the instruments to cosmic-rays give significant influence on the results. Environmental radiation measurements at various altitudes on Mt. Fuji were carried out using a scintillation spectrometer with 3″φ spherical NaI (Tl), a pressurized ionization chamber (PIC), an air-equivalent ionization chamber (IC), thermoluminescence dosimeters (TLD), radiophotoluminescence glass dosimeters (RPLD) and NaI (Tl) scintillation survey meters so that the response characteristics of these instruments to cosmic-rays could be clarified. Cosmic-ray contributions for all instruments were correlated with counting rate over 3 Me V by the spectrometer. Each contribution can be estimated by measurement of the counting rate. Conversion factors (nGy/h/cpm) for IC, PIC, TLD, RPLD and NaI survey meters (TCS166 and TCS121C) were 0.33, 0.32, 0.25, 0.24, 0.06 and -0.01, respectively. Self-doses of these instruments were estimated by measurements at Nokogiriyama facilities of the Institute for Cosmic Ray Research, University of Tokyo. Self doses for TLD and RPLD were approximately 6 nGy/h. The self dose effect should be taken into consideration in environmental dose measurements. These data are expected to be useful in estimating the cosmic-ray contribution and self dose in the measurement of environmental gamma-ray dose.