An extension of 4πe·X-γ coincidence technique is described to measure the absolute disintegration rate of85Sr.This nuclide shows electron capture-gamma decay, and 514 keV level of85Rb is a meta-stable state with half life of 0.958μsee. Therefore, the conventional 4πe⋅X-γ coincidence technique with about 1μsec of resolution time can not be applied to this nuclide. To measure the absolute disintegration rate of this, the delayed 4πe⋅X-γ coincidence technique with two different resolution times has been used. The disintegration rate was determined from four counting rates of electron-X ray, gamma ray and two coincidences, and the true disintegration rate could be obtained by extra poration of the electron-X ray detection efficiency to 1. Two resolution times appearing in the calculation formulas were determined from the chance coincidence between electron-X ray and delayed gamma ray signals. When the coincidence countings with three different erent resolution time were carried out by one coincidence circuit, the results calculated from all combinations did not agree each other. However, when the two coincidence circuits of the same type were used to fix the resolution time, a good coincidence absorption function was obtained and the disintegration rate was determined with accuracy of±0.5%. To evaluate the validity of the results the disintegration rates were measured by twoNaI (Tl) scintillation detectors whose gamma-ray detection efficiency was previously determined and both results were agreed within accuracy of±0.5%. This method can be applied with nearly same accuracy for the beta-gamma decay nuclide possessing a meta-stable state of the half life below about 10 μsec.
The quenching effect for halogenated benzenes, methanes and ethanes have been investigated. The halogen quenching was accurately measured using the internal conversion electrons emitted from113Sn-113mIn. From the quenching constants determined by the Stern-Volmer plots with respect to various halogen quenchers, the following results have been obtained. (1) The quenching constants increase with the number of halogen substituents, so as linearly in halogenated benzenes and exponentially in halogenated methanes and ethanes. Even the isomers of halogenides have different quenching constants. (2) There is a linearity between logarithm of the quenching constant and a polarographic half wave reduction potential. (3) Electron excitation provides larger quenching constants than UV excitation for halogenated methanes. Based on these results, the mechanism of halogen quenching have been discussed in connection with the exciplex formation.
In 1938, S. V. Raghava Rao reported that a crystal of HgXSCN (X=halogen) has photropic properties and in 1955, the author reported the mechanism of the phototropy is identical with that ofHgI2·2HgS.However, a behavior of S, I and C atoms in the crystals irradiated by sunlight was not known. Purpose of this paper is to clarify the behavior of these atoms by using radioactive tracer technique. The results obtained show that when electrons belonging to S2-or I-ions absorb photons and are excited to upper state, these electrons leave behind neutral S or I atoms, which diffuse thermally toward the crystal surface and escape into atmosphere.14C atoms do not escape. S atoms are more sensitive to light than I or C atoms.
For the purpose of calculating absorbed dose to humans from167Tm-citrate, the wholebody retention studies using 5 rats were carried out. Up to 40 days following intravenous injection of167Tm-citrate, the whole-body counts were monitored with a animal counter. The whole-body retention curve was obtained with three exponentaial components. Namely, the 26% of the injected187Tm-citrate had a biological half-time of 3.4 hours, 12.5% had a biological half-time of 99 hours and 61.5% had a biological half-time of 106 days. These results indicate, that three components consist of the rapid clearance from the kidneys, the retention in the liver and other soft tissues with relatively long half-time and the retention in the bones with long half-time. Based on these biological data and the MIRD Committee method, the average dose estimates to the bone and whole-body from intravenous administration of 1 mCi167Tm-citrate were 7.08 rads and 1.28 rads, respectively.