Tsutomu Sekine

Precipitation scavenging studies of radionuclides in air using cosmogenic ^7Be

Precipitation scavenging of 7Be in air was studied, especially during winter. A nearly linear relation between precipitation and 7Be deposition was found, not only in the winter monthly data, but also in the individual snowfalls. The 7Be concentrations in snow water and in air were measured simultaneously. Washout of 7Be-bearing aerosols in air was directly observed. But in the overall precipitation phenomenon, it appeared that rainout was the predominant process in wet scavenging of 7Be. Then, the linear relation between precipitation and 7Be deposition was introduced and an equation which was composed of two terms corresponding to washout and rainout was derived from integration of the empirical formula of deposition for individual precipitation.

Distribution of Artificial Radionuclides in Abandoned Cattle in the Evacuation Zone of the Fukushima Daiichi Nuclear Power Plant

The Fukushima Daiichi Nuclear Power Plant (FNPP) accident released large amounts of radioactive substances into the environment. In order to provide basic information for biokinetics of radionuclides and for dose assessment of internal exposure brought by the FNPP accident, we determined the activity concentration of radionuclides in the organs of 79 cattle within a 20-km radius around the FNPP. In all the specimens examined, deposition of Cesium-134 (134Cs, half-life: 2.065 y) and 137Cs (30.07 y) was observed. Furthermore, organ-specific deposition of radionuclides with relatively short half-lives was detected, such as silver-110m (110mAg, 249.8 d) in the liver and tellurium-129m (129mTe, 33.6 d) in the kidney. Regression analysis showed a linear correlation between the radiocesium activity concentration in whole peripheral blood (PB) and that in each organ. The resulting slopes were organ dependent with the maximum value of 21.3 being obtained for skeletal muscles (R2 = 0.83, standard error (SE) = 0.76). Thus, the activity concentration of 134 Cs and 137Cs in an organ can be estimated from that in PB. The level of radioactive cesium in the organs of fetus and infants were 1.19-fold (R2 = 0.62, SE = 0.12), and 1.51-fold (R2 = 0.70, SE = 0.09) higher than that of the corresponding maternal organ, respectively. Furthermore, radiocesium activity concentration in organs was found to be dependent on the feeding conditions and the geographic location of the cattle. This study is the first to reveal the detailed systemic distribution of radionuclides in cattle attributed to the FNPP accident.

Effects of radioactive caesium on bull testes after the Fukushima nuclear plant accident

We aimed to investigate the effect of chronic radiation exposure associated with the Fukushima Daiichi Nuclear Plant accident on the testis from 2 bulls. Estimated dose of internal exposure in one bull was 0.7–1.2 mGy (134Cs) and 0.4–0.6 mGy (137Cs) and external exposure was 2.0 mGy (134Cs) and 0.8 mGy (137Cs) (196 days). Internal dose in the other was 3.2–6.1 mGy (134Cs) and 1.8–3.4 mGy (137Cs) and external dose was 1.3 mGy (134Cs) and 0.6 mGy (137Cs) (315 days). Sperm morphology and spermatogenesis were within normal ranges. 134, 137Cs radioactivity was detected but Cs was not detectable in the testis by electron probe microanalysis. Thus, adverse radiation-induced effects were not observed in bull testes following chronic exposure to the above levels of radiation for up to 10 months. Since we could analyse a limited number of testes, further investigation on the effects of ionizing radiation on spermatogenesis should be extended to more animals.

Radiolytic formation of Tc(IV) oxide colloids

Summary Technetium(IV) oxide colloids were radiolytically formed by γ irradiation of aqueous solutions of pertechnetate (TcO4−). Pertechnetate solutions (5.5×10−5-2.9×10−4 M) were irradiated with bremsstrahlung from an electron linear accelerator at 40 and 17 °C. The color of irradiated solutions gradually changed to brownish black, suggesting the formation of Tc(IV) oxide colloids (TcO2·nH2O). A transmission electron microscopy (TEM) analysis showed that the size of colloids distributed around 30 to 130 nm in diameter. The characteristic X-rays from technetium and oxygen were simultaneously detected from colloid particles at the TEM measurements. Round-shaped colloids were produced by irradiation at 40 °C, whereas irregular-shaped colloid particles composed of tiny particles (2 nm in diameter) were produced at 17 °C. The concentration of TcO4− in the target solution gradually decreased with an increase of the absorbed dose, corresponding to an increase of the colloid yield. The yield of colloids sharply increased in the solution deaerated by Ar bubbling before irradiation, but strongly suppressed in the solution saturated with oxygen (O2) or nitrous oxide (N2O) gas. The fact suggests that hydrated electrons play an important role in the course of the reduction of TcO4− and that Tc(IV) oxide colloids were formed via successive disproportionation reactions of Tc(VI) and Tc(V). The formation mechanisms of Tc(IV) oxide colloids are discussed.

Production of positron emitters of metallic elements to study plant uptake and distribution

The metallic positron emitters 52Mn, 52Fe and 62Zn, the elements of which are essential nutrients for plants as well as for animals, have been produced for a new tracer method in plant physiology. The tracer method utilizes the detection of annihilation γ-rays, like PET in nuclear medicine, to obtain two-dimensional images on a plant as well as to obtain radioactivity counts at specified points in a plant; this method allows us to observe the tracer movement in a living plant without touching the test plant. The previously reported methods of radiochemical separation of these metallic positron emitters from targets were partly modified from the view of their use in plant physiology. Radionuclidic impurities remaining in the final solutions were examined by γ-ray spectrometry, and their influences on the above-mentioned measurements are discussed. From the experiments on a barley plant, the speeds of 52Mn2+ ion and 52Fe3+-mugineic-acid complex have been obtained for the first time to be 0.2 cm/min and 1.0 cm/min, respectively.

Integral cross section of the 99Tc(γ, γ′)99mTc reaction in the 15–50 MeV energy region

Photoexcitation of radioactive 99Tc was studied by irradiation with 15–50 MeV bremsstrahlung. The integral cross sections of the 99Tc(γ, γ′)99mTc reaction and the reference 115In(γ, γ′)115mIn reaction were found to be nearly constant as (5.8 ± 1.0) × 10−27 cm2 MeV and (9.3 ± 0.4) × 10−27 cm2 MeV, respectivel in the given energy range. The large second increase of the cross section described in earlier reports was observed neither for 115In nor for 99Tc.

Chromatographic separations of fac- and mer-tris(β-diketonato)chromium(III) complexes

Abstract In order to find the factors that affect the separation of metal chelates, the elution and distribution behaviour of chromium(III) complexes coordinated with unsymmetrical β-diketones were studied in various solvents using silica gel as an adsorbent. The differences in the specific retention volumes or adsorption distribution coefficients of metal chelates are ascribed to the differences in the total energies of interaction between the chelate molecule and the adsorbent surface. The total energy S 0 is expressed by three independent terms as follows: S 0  aG i + bG j + c where G i and G j are parameters representing the interaction energies of the functional groups containing the substituents in a β-diketone. Using the relative values of G i and G j for the functional groups, the ratio of the distribution coefficients of Cr(acac) 3 to a tris(β-diketonato)chromium(III) was evaluated. On the basis of a linear relationship between the experimental and calculated distribution coefficients, the quantitative separation of metal chelates in the silica gel adsorption chromatography is discussed.

Photoluminescence switching with changes in the coordination number and coordinating volatile organic compounds in tetracyanidonitridorhenium(V) and -technetium(V) complexes.

Six-coordinate distorted octahedral tetracyanidonitridorhenium(V) and -technetium(V) complexes with a volatile organic compound (VOC) coordinating at the trans position of a nitrido ligand, (PPh4)2[MN(CN)4L] (M = Re, L = MeOH, EtOH, acetone, or MeCN; M = Tc, L = MeOH), and five-coordinate square-pyramidal tetracyanidonitrido complexes without an axial ligand, (PPh4)2[MN(CN)4] (M = Re or Tc), were synthesized and characterized. Single-crystal X-ray structural analysis was carried out for (PPh4)2[MN(CN)4L] (M = Re, L = MeOH, EtOH, or acetone; M = Tc, L = MeOH) and (PPh4)2[ReN(CN)4]. All complexes studied showed photoluminescence in the solid state at room temperature. Reversible luminescence switching between six- and five-coordinate rhenium(V) complexes and between the relevant six-coordinate rhenium(V) complexes except that between the MeCN and acetone complexes was achieved by exposing them to VOC vapor in the solid state at room temperature. Luminescence changes were observed from the five-coordinate technetium(V) complexes in a MeOH vapor atmosphere in the solid state. In contrast, no vapochromic luminescence was observed from the five- and six-coordinate complexes in an acetone vapor atmosphere.

Recoil Implantation Reactions in Binary Mixtures of Catcher Complexes and in Mixed Ligand Catchers

Recoil implantation reactions were studied in binary mixtures of catcher complexes of tris(/i-diketonato)metal(III) and in singlecomponent catcher complexes of Cr(acac)„(dbm)3 _„ where η = 1 and 2. For the mixtures of M(acac)3 and M(dbm)3, the products of Cr(acac)3 and Cr(dbm)3 were obtained as major components while Cr(acac)2(dbm) and Cr(acac)(dbm)2 were seen as minor components. For the single component catcher complexes, predominant chemical species were parent retention type compounds. In addition to retentions there were product distributions which indicated a strong preference for acac pickup. The results were interpreted by a model which involves displacement reaction as a main process and ligand pickup reactions as side processes.

Deuterium migration in titanium during deuteron irradiation observed by proton spectra of the d(d,p)t reaction

From analysis of proton spectra associated with the d(d,p)t reaction, deuterium depth profiles in titanium during 130-keV deuteron irradiation at temperatures from 260 to 360 K were obtained as a function of the irradiation time. This nuclear reaction analysis technique (NRA) was applicable to in situ depth profiling in the region from the surface to the depth of 0.6 μm in titanium. The depth resolution varied depending on the depth; 0.07 μm at the surface and 0.15 μm at the depth between 0.2 μm and 0.6 μm. The observed depth profiles gave a clue to the dynamics of deuterium migration in titanium.