Yasushi Nishiwaki

An approximation of γ-ray buildup factors by geometrical progression

Geometrical progression formulas were derived for the approximation of the γ-ray dose, energy, and energy absorption buildup factors. The approximation formulas have the form 1 + (B−1)(KX−1)(K−1), where B and K are the two parameters and X is the source-detector distance in the medium in mean free paths. The results of the approximations were in good agreement with the basic data for all the materials used in the basic data, for the energy range of 0.5 to 10 MeV, and for thicknesses up to 20 mean free paths. An approximation using the method for the transmission probability for γ-rays obliquely incident on finite slabs was also attempted. Two parameters, B and K, of the geometrical progression form could be represented by monotonic functions of log E, in which the values of the two parameters changed monotonically with the atomic number of the media. Further, the four parameters which were used to represent B and K as linear functions of log E, and the six parameters used to represent B and K as quadratic functions of log E were also observed to change monotonically with the atomic number of the media. Therefore, the values of these parameters can be estimated for any media of different atomic number by interpolation.

Analysis of Transmitted Gamma-Rays by Multiple Scattering Method, (I):Gamma-Rays Transmitted through Slabs of One Material

Dose buildup factors and number spectra of γ-rays transmitted through a homogeneous finite slab have been estimated by the multiple scattering method, taking into account scattering — including back scattering — up to the fourth order. The calculations were performed for 1.0, 3.0, 6.0, 8.0 and 10.0 MeV γ-rays normally incident on lead, iron and water slabs of thicknesses from 1 to 15 mfp. The results of the above calculations are in good agreement with those from other calculations, such as by Monte Carlo and response matrix methods, especially for heavy shielding materials of practical importance and γ-rays of high incident energy. Further, a method is proposed with which the contribution to the total dose buildup factor by the γ-rays of the fifth and higher orders of scattering can be estimated approximately. With this method, good agreement was obtained with the dose buildup factor calculated by the Monte Carlo method, even for light shielding materials and γ-rays of low incident energy.

DECONTAMINATION OF FISSION PRODUCTS ON HUMAN SKIN AND HAIR.

Abstract —The contamination and decontamination of human skin and hair may be influenced not only by the colloidal adsorption on the surface or absorption of radioactive substances into human tissue, but also by various physical, chemical and biological factors which make a reproducible decontamination experiment difficult. Therefore, in order to compare the efficiencies of various decontaminating agents we have employed a special device with which the conditions of decontamination could be kept more or less constant. In these experiments, water, citric acid and the powerful chelating agents EDTA and DTPA were used for the purpose of decontamination of fission-products on a non-living, human skin sample and on hair. The decontaminated percentage (Dt), expressed in total gross activities, and the change of the decontaminated radioactivities per unit volume of eluting solution were measured. Judged on the basis of the decontaminated percentage (Dt), the chelating agents were similarly effective in decontaminating the samples of human skin as with those of human hair. The radioactivities rapidly removed in the initial eluting solution seemed to indicate that there was a component that can be easily decontaminated with the chelating agents. The persistently remaining activity appearing in the eluting solution after elution with 300-400 ml seemed to indicate that some of the strongly fixed or reacted component might have been gradually eluted out with the chelating agents. The decontaminated percentage (Dn) of each nuclide as estimated by the analysis of the γ-spectrum is given to show an order of magnitude. The similarity in the mode of decontamination between the samples of human skin and those of hair may indicate, at least partly, the possibility of the existence of a competing effect of chelating agents against some of the reactions between metals in fission-products and proteins, for instance, keratin, collagen and so on which exist commonly in both samples. Although it is anticipated that the use of chelating agents may enhance the absorption of some radioactive nuclides through the skin, if the solution containing the chelating agents were used for the decontamination of skin and hair in the form of a shower or by running water over the contaminated skin or hair to minimize the skin absorption, it may be extremely useful in some cases.

Basic Consideration on the Method of Counting Low Energy β-particles with Liquid Scintillation

Liquid scintillation detectors with single and duel photomultipliers were investigated and compared. Poor light collection in the detectors led to the design of a new semispherical type vessel made of glass. The spherical part was plated with silver except for the base. All light except for that directed to the base was reflected back toward the base. The counting efficiency of the device was studied for beta particles from C/sup 14/ and H/sup 3/. Results were very favorable for C/sup 14/ but somewhat unfavorable for H/sup 3/. (L.N.N.)