Norio Takeuchi

Absolute measurement of 166mHo radioactivity and development of sealed sources for standardization of γ-ray emitting nuclides

Holmium-166m has a long half life (1200 yr) and emits a large number of gamma-rays between 80 and 1400 keV. These characteristics are very suitable for gamma-ray calibration sources, therefore, the absolute activity of 166mHo was measured and several sealed sources were produced to be used as reference sources for the secondary standardization systems for gamma-ray emitting nuclides. In this project, seven metal sealed sources and ten point sources were produced and several of these sources were transferred to the secondary standard laboratories to complete the traceability scheme.

Determination of gamma-ray emission probabilities for 75Se, 166mHo and 192Ir by a self-consistent method

Abstract The gamma-ray emission probabilities for 75 Se, 166m Ho and 192 Ir have been measured precisely using a 4πβ(ppc)-γ(HPGe) coincidence system. When determining the gamma-ray detection efficiency function, these nuclides were used as secondary standards in conjunction with a few primary standard sources. This method is considered to give self-consistent results and to be effective when there are insufficient suitable standards.

Determination of the emission probabilities of the principal γ-rays for 134Cs to a high precision

While multi-gamma-ray emitting nuclides such as 75Se, 134Cs and 152Eu have reasonably well-defined decay scheme, some inconsistencies still remain. Detailed evaluations and weighted-mean analyses result in the recommendation of gamma-ray emission probabilities with small uncertainties, although significant deviations exist in the measured values. Therefore, the gamma-ray emission probabilities of 134Cs have been measured to a high precision after an extremely accurate calibration of detection efficiency. The resulting data agree extremely well with the evaluated values in IAEA-TECDOC-619 (IAEA, X-ray and gamma-ray standards for detector calibration, IAEA-TECDOC-619, IAEA, Vienna, 1991).

High accuracy measurement of the relative efficiency curve and determination of gamma-ray relative intensity for 38Cl

Relative efficiency curves were accurately determined for Ge gamma-ray detectors from measurements for radionuclides which emit two gamma-rays with essentially the same emission probabilities. The relative intensity of the 1643 and 2167 keV gamma-rays from 38Cl was determined to be 0.7496 (11) by using these highly accurate efficiency curves.

GAMMA-RAY EMISSION PROBABILITIES OF 182TA

Abstract 182 Ta sources were produced, and the disintegration rate and γ -ray emission probabilities were measured as an aid in using this radionuclide as a calibrant for HPGe detectors. Metal powders proved to be the most appropriate sources, and the disintegration rate was determined with an uncertainty of less than 0.4%. Improved data with reduced uncertainties were also obtained for the γ -ray emission probabilities.

Radioactivity standards for 192Ir brachytherapy sources

Abstract Absolute radioactivities of brachytherapy 192 Ir metallic sources of single pin and hairpin types are nondestructively determined with a microcalorimeter. In order to convert the complete decay energy evolved from the sources into thermal energy, a radiation absorber made of tungsten is used. Overall uncertainties of the activity determinations are estimated to be ±3.1% for the single pin source and ±4% for the hairpin source at the level of 3σ.

Radioactivity measurements of 192Ir wire sources with a microcalorimeter

Abstract Radioactivities of metallic 192 Ir sources are measured with a microcalorimeter nondestructively. In order to convert the complete decay energy evolved from the source into thermal energy, a tungsten block is used as radiation absorber. The sample sources measured are four thin wires of Ir/Pt alloy with dimensions of 0.1 mm o × 10 mm 1 , each coated by 0.1 mm thick platinum, giving the final diameter of 0.3 mm o . Overall uncertainty of the measurement for some 60 MBq activity is ±3.2%. Measurements of the wire sources with an ionisation chamber give smaller activities which are smaller by 10% than those from microcalorimetry mainly because of the autoattenuation effect.