The rate of the elution of radionuclides from solidified wastes depends mainly on the dissolution at the surface of the solidified wastes and the diffusion process in the solidified body. Concerning the later process, several methods to determine the effective diffusion coefficients were reviewed and newly developed theoretically in this study. It was revealed that the coefficients representing the diffusion of radionuclides migrating in the solidified wastes can be obtained through measurements of radionuclides which were leached out from a solidified body, with limited or unlimited length, into a finite volume of water.
We have observed properties of radioactive fallout originated from the first, the second, the third, the fourth and the fifth Chinese nuclear explosions. The differences in gross beta-activities, activities per unit volume and their particle sizes of highly radioactive particles are discussed with relation to the differences in burst conditions among the five explosions from which they originated. It was found that radioactivities of the highly radioactive particles were roughly proportional to their volumes. The differences in the radioactive decay rates of highly radioactive fallout particles were found in connection with their colors. From the results of decay characteristics of gross beta-activities and γ-ray spectra of fallout samples, it was found that the contribution of radioactivities of 239Np in samples from the fifth Chinese explosion was larger than that from the third Chinese explosion. In comparison between the γ-ray spectra of highly radioactive fallout particles from the third and the fifth Chinese explosions, the particles from the third Chinese explosion were enriched in 95Zr+95Nb and impoverished in 103Ru, while on the particles from the fifth Chinese explosion, the reverse of phenomenon above mentioned was observed.
In measuring α ray spectra of radioactive airborne dust collected on a filter paper, the presence of α emitters to be detected is masked out by Rn and Tn daughters in atomosphere. Contributions of Tn daughters to α ray spectra of airborne radioactive materials were evaluated for two types of cellulose asbestos filter paper, HE-40 (Toyo) and HV-70 (Honing Worth & Vose), employed in routine air sampling, using the TMC 1024 pulse height analyzer with a silicon semiconductor detector. The distribution was also examined by α counting of thin stripped fragments of the filter paper, and was found to be exponential. On the basis of the results obtained, the collection efficiency of HE-40 and the absorption of α particle in the filter paper are discussed.
In handling radioactive materials, various kinds of protective clothing made of polymeric films are employed for the protection of radioactive contamination. The permeation rate of the tritiated heavy water and its vapour through polymeric film, such as PVC, polyethylene, rubber was measured by using an ionization chamber with a vibrating reed electrometer. On the basis of the results obtained, internal exposure of the person wearing the protective clothing is evaluated and discussed.
The authors emphasized in the former paper that the measured values in the field of radiological protection are inevitably concerned with the uncertain factors which can never be dissolved by mere improvement of measurement techniques. A concept of “Entropy”popularly used in information theory was introduced in this paper in order to give a quantitative estimation of the uncertainty which appears in the problem of internal contamination measurement. Body retention of the radioactive contaminant after a single intake changes with time according to the physical decay and biological elimination. Hence we have uncertainty in case of estimating the initial amount of contamination from a single value of one-point sampling and measurement. When the detected body burden is q (μCi), the probability with which the initial intake Qo (μCi) may have been over the predecided reference value qo (μCi) was given as follows, p (Qo≥qo) =1-Teff/τlog2qo/q where τ is the interval of measurement and Teff is the effective half life. Apparently, p (Qo<qo) =Teff/τlog2qo/q The authors also gave a graphical presentation of the entropy and discussed the effectiveness of internal contamination sampling program.