Authors:T. Hashimoto, F. Ishizuka, Y. Yoneyama, T. Kubota and N. Fukuyama
The time files due to radioactive decay events were analyzed for the selective extraction of successive alpha-decay pulse events in millisecond orders, such as216Po (145 ms, thorium series),217At (32.3 ms, neptunium series), and215Po (1.78 ms, actinium series) after respective preceding parents decay, using a multiple time interval analysis (TIA-MTA) technique from both theoretical and experimental viewpoints. In the theoretical treatments, the detection sensitivities of each correlated event in natural decay series was compared with more generalized conditions. It was noteworthy that the evaluated detection sensitivity had increased proportionally with shorter half-lives in the following order:214Po>215Po>217At>216Po.Finally, the present TIA was applied to the clarification of thorium series disequilibrium states in Tamagawa (Akita, Japan) Hot Spring waters. Activities of224Ra were evaluated to be 3.41±0.38 and 0.60±0.08 Bq/l at the upper and lower stream, respectively. The results from activity ratios of radium to thorium isotopes showed a preferential precipitation of radium isotopes in comparison with thorium, reflecting the sensitivity to the lowering acidity of strongly acidic hot spring waters in the lower end of the stream.
Authors:T. Fukuyama, N. Kihou, H. Fujiwara, M. Nakashima and E. Shiratani
In order to assess the effect of marine and terrestrial environmental change in the last decades on the sedimentation environment
in Ariake Bay, we collected three sediment cores. The concentrations of natural and anthropogenic radionuclides, major elements,
and rare-earth elements were measured using gamma-spectrometry and neutron activation analysis. Vertical distributions of
both radionuclides and sedimentation rates, determined using Cs-137 and Pb-210ex dating methods, varied significantly among the sites.
Authors:T. Hashimoto, K. Sato, Y. Yoneyama and N. Fukuyama
Some improvements of the detection sensitivity in pulse time interval analysis (TIA) based on selective extraction of successively - correlated decay events within millisecond order from random or background events, were established by the utilization of PSD, to reject /-pulses from -ones and a simple chemical procedure of radium separation, together with the use of well resolved scintillator. By applying the PSD, the contribution of -decay events was completely eliminated in both the -spectra and the TIA distribution curves as well as the improvement into clear energy resolution and the enhancement of detection sensitivity for the TIA. As a result, the TIA and -spectrometric analysis of226Ra-extract showed the existence of223Ra (Ac-series) and /-correlated events with correlated life (due to 0.16 ms due to214Bi()
214Po()) along with a singly well resolved -peak to be useful for the determination of226Ra (U-series). The difference of half-lives (145 and 1.78 ms) due to216Po and215Po (direct daughters of224Ra for Th-series and223Ra for Ac-series, respectively) was also proven for the possibility of the simultaneous determination of both correlated events by using the TIA/PSD combined with chemical separation and liquid scintillation counting method. Finally, the simultaneous determination of three natural decay series, which include U-, Th- and Ac-series nuclides, have been conveniently carried out for some environmental samples using the present method combined with225Ra yield tracer (Np-series).
Authors:T. Fukuyama, Md. T. Rahman, N. Kamata, M. Tokizane, Y. Fukuda and I. Ryu
Fluorous multi-phase bromination reaction of alkenes could be successfully transformed to a continuous microflow system in which a fluorous polyether, Galden® HT135, is employed as a recyclable molecular bromine support. This microflow bromination of alkenes could be carried out without any temperature control or an inert gas atmosphere. The circulatory continuous microflow reaction system for bromination of cyclohexene was created which gave 8.3 g (85%) of dibromocyclohexane after continuous operation for 6 h.