BEIR III committee has issued an extensive review on the effects of low level radiations on human population. The review deals with the levels of radiation exposure for US people, scientific principles in analysis of radiation effects and describes how the risks of genetic and somatic effects are estimated. Major advances from the previous report (BEIR I) are: Introduction of three different dose-response models (linear, linear-quadratic and quadratic) for the estimation of risk of cancer induction, attempt to estimate cancer risk based on the incidence in addition to the mortality, and consideration of influence of the sex and the age at exposure on cancer induction. Follow-up studies at RERF in Hiroshima and Nagasaki are contributing greatly in providing basic data. Review of selected studies on record such as MANCUSO et al., STERNGLASS and others, and analysis of the effects other than cancer are also useful.
This work deals with measurements of absorbed dose in bone due to beta-rays using thermoluminescent dosimeters. The calibration of the CaSO4: Dy dosimeters was performed by immersing them in a solution 90Sr-90Y. The dose rate was then computed from the known concentration of the solution. Theoretical calculations based on the Monte Carlo method were made for beta-emitting radionuclides contained in small polypropylene tubes. Comparison between the results of measurements and calculations shows that the model designed for Monte Carlo calculation is reasonable.
An uncertainty in the method of determination of radioactive iodine (131I) in milk with a NaI (Tl) scintillation spectrometry of which procedure manual is provided by the Science and Technology Agency is analyzed on the basis of a train of the actually measured data, and a minimum detectable activity in a routine monitoring is estimated. Judging from the error analysis, the total systematic error of the concentration of 131I in milk is about 10pCi/l, which is mainly attributed to the presence of natural radioactive nuclides except 40K, and the total random error is ±6 pCi/l resulting from the counting error and the deviation in gain adjustment. If we define a minimum detectable activity as the sum of systematic error and three times random error, it would be about 30pCi/l for 131I, But in case some other unexpected nuclides are contained in milk, this method cannot afford to determine the concentrations precisely.
Characteristics of Li2B4O7 TL element was studied for the design of new personnel dosimeter. According to the results, a eight-element thermoluminescent dosimeter (TLD badge) for gamma ray, beta ray and neutron has been developed using Li2B4O7(Cu) and CaSO4(Tm) elements. Each element is measured by an automatic TLD reader connected into computer system. Each dose and effective energy of beta ray are able to be evaluated by this TLD badge. One Li2B4O7 and one CaSO4 elements for gamma ray are shielded to provide interpretation of 1, 000mg/cm2 tissue depth dose and two Li2B4O7 elements are used for beta absorbed dose interpretation. Three 6Li210B4O7 and one 7Li211B4O7 elements are used for thermal and fast neutron. Minimum detectable amount of this badge is 2 mrem for gamma ray and 20 mrem for beta ray in the mixed field.
This paper describes a calibration method of a pair of 12.5cm diameter phoswich detectors for the measurement of the amount of Pu in lungs. The phoswich detector consists of a thin crystal (3mm) of NaI (Tl) backed by a thick crystal (50mm) of CsI (Na). The calibration factor obtained from a phantom was corrected for Pu isotopic composition and the X-ray absorption in the soft tissue. The X/α ratios of several Pu samples having different isotopic compositions were calculated, in order to take into account the difference of the isotopic composition used in the phantom from that of an inhaled person. For sixty male subjects, the chest wall thicknesses were measured using ultrasonic device, and an emprical equation, which expresses the relationship between chest wall thickness and body parameters such as weight and height, was derived. The minimum detectable amount of typical reactor-grade Pu, which was obtained by the phoswich detector assembly, was 7nCi for an average subject.