For over four decades, a linear nonthreshold (LNT) model has been used for radiation protection purposes. In the United States of America, the National Council on Radiation Protection and Measurements (NCRP) established Scientific Committee 1-25 in 2015 to prepare a commentary to review recent epidemiologic data from studies with low doses or low dose rates and from the Life Span Study of atomic-bomb survivors to determine whether these epidemiologic studies broadly support the LNT model. In May 2018, NCRP published Commentary No. 27 “Implications of recent epidemiologic studies for the linear nonthreshold model and radiation protection”, noting that the ongoing development of science requires a constant reassessment of prior and emerging evidence to assure that the approach to radiation protection is optimal, even if not necessarily perfect. Based on the current epidemiological data, NCRP concluded that the LNT model (perhaps with excess risk estimates reduced by a dose and dose rate effectiveness factor) should continue to be utilized for radiation protection purposes. The Commentary will be used to support the work of NCRP Council Committee 1 who are charged to develop current radiation protection guidance for the United States, ultimately updating and expanding the basic radiation protection recommendations of NCRP Report No. 116 published in 1993. This review provides an outline and summary of the key points of NCRP Commentary No. 27.
Fifty-five years after discovery of x-rays by Wilhelm Conrad Röntgen in 1895, International Commission on Radiological Protection (ICRP) established a committee on permission internal exposure. Natural and man-made radionuclides can enter human body, cause damage effect and lead to health risk; on the other hand, radionuclides can cure cancers and other non-cancer diseases by irradiating the malignant cells and tissues. The radiation doses delivered to the tissues and organs are inevitable to assess risk or to judge the benefit of application of radiation on humans. In this article, basic methodology for dose assessment of internally deposited radionuclides is reviewed. After brief introduction of interactions and effects of radiation, the biokinetic models developed by ICRP for incorporation of radionuclides in humans are described. Then, the dosimetric formula generalized by ICRP and Committee on Medical Internal Radiation Dose (MIRD) is presented. Treatment of decay products and uncertainty analysis in internal dosimetry are especially addressed. Moreover, applications of internal dosimetry in radiation protection, internal exposure monitoring, radon inhalation dosimetry and nuclear medicine are presented with several calculation examples. At last, the future perspective of internal dosimetry is discussed. In an appendix basic internal dosimetric quantities are provided.
In this study, to estimate the recent tritium concentration and its variation with latitude and time in Japan, environmental water samples were taken monthly from June 2014 to October 2016 in Okinawa Island, subtropical region of Japan. The inland water samples were taken from two springs and the drop water samples were taken in a limestone cave. The samples were distilled to remove impurities and then electrolysed using electrolytic enrichment system. Each of the enrichment samples was mixed with the liquid scintillation cocktail, and the tritium concentration was measured with a low background liquid scintillation counter. Arithmetic mean ± standard deviation for the tritium concentration of Morinokawa (spring water), Kakinohanahikawa (spring water) and Gyokusendo (cave drop water) samples were estimated to be 0.13 ± 0.04 Bq L-1, 0.12 ± 0.03 Bq L-1 and 0.13 ± 0.03 Bq L-1, respectively. The comparison between these results and reported data suggested that the latitude effect is one of factors in the relatively low tritium concentration observed in Okinawa Island.
The Basic survey as a part of the Fukushima Health Management Survey was a self-administered questionnaire that asked subjects to record and send back information on their behavior in the 4 months after the Fukushima disaster. These behavior records were then digitalized, and individual estimates of external radiation exposure were made using daily ambient dose rate maps. Several issues arose in the process from receiving the completed questionnaires, estimating doses, and informing residents of the results. After sending out the questionnaires, a large number (8,000 responses per day at its peak) were returned over a short period, and these needed to be processed. To aid this, the number of staff involved in digitalizing the hand-written questionnaires was greatly expanded. Another issue was how to increase the response rate. While actions taken to raise the response rate did increase the number of responses to some extent, the response rate of the prefecture overall did not increase greatly. Such problems may be encountered in large-scale behavior surveys should another disaster occur in the future. This report gives an overview of these problems and how they were dealt with, which will provide a resource for public dose assessments should another disaster occur in the future.