Toshio Muto

Determination of the Purity of Gold Alloys Using Gamma-Ray Transmisson Techniques.

Triple and dual energy γ-ray transmission (TEGAT and DEGAT) techniques were examined to determine nondestructively the purity of gold alloys. The experimental system was composed of a radioactive source 152Eu (31 MBq) emitting many energies of γ-ray and a high-purity germanium detector having a high-energy resolution. The TEGAT technique suggested that the purity of gold alloys of 1–5 mm thickness can be determined with a precision of more than 99% under an allowance range condition of two karats. By the DEGAT technique, on the other hand, the purity of gold alloys of 3–5 mm thickness could be determined with 95–99% precision under the same condition as above. For the DEGAT technique, it was assumed in this study that the mass attenuation coefficient of silver was equal to that of copper. It was found that the γ-ray transmission techniques can be effectively applied for the measurements of the purities of thick gold alloys which are otherwise impossible to determine by fluorescence X-ray analysis.

Examination for Analysis of Minerals by Means of Dual Energy Gamma-ray Transmission Techniques.

For application of dual energy gamma-ray transmission techniques to practical mineral grade analysis, some problems including selection of gamma-ray energies, influence of sample thickness and main causes of errors in measurement have been examined.The relationships between the R-values (the ratio of mass attenuation coefficients for low and high energy gamma-rays) and the effective atomic numbers for various samples (e.g., iron ore, coal and coke, limestone, minerals and gem stones) were determined using different energy combina-tions of gamma-rays from 152Eu. On the basis of the experimental results, the optimum conditions for analysis of minerals were discussed.

Examination for Practical Use in Dual Energy Gamma-ray Transmission Techniques. Application to Grading of Gold Alloys.

For practical use of dual energy gamma-ray transmission techniques in various fields, necessary conditions have been examined experimentally.The study revealed the necessary conditions shown in the following : (1) the shape and size of the collimator aperture for a gamma-ray beam must be changed according to those of a sample to be measured, (2) a sufficiently intense gamma-ray source is required which provides counting rates of tens of thousands per minute, (3) the ratio of N/N0 must be in a range of 0.8-0.1, and (4) the value of R with a minimum error calculated should be adopted.

Determination of residual activities in 99mTc generators and 81mKr generators.

The residual activities present in spent 99Mo-99mTc generators and 81Rb-81mKr generators were determined from a view point of the disposal of radiopharmaceuticals. The results showed that seven kinds of residual nuclides such as 95Zr-95Nb, 103Ru, 90Sr, etc. were found in 99mTc generators with maximum level of 740 Bq/3.7 GBq (0.02 muCi/100 mCi) at one year after the reference date. In 81mKr generators one year old, six nuclides such as 57Co, 83Rb, 84Rb and others remained and these activities were less than 3.7 kBq/370 MBq (0.1 muCi/10 mCi). On the basis of these data, the disposal of 99mTc generators and 81mKr generators is discussed.