Y. Oura

The nuclear interaction at Oklo 2 billion years ago

Abstract We re-examine the effort to constrain the time variability of the coupling constants of the fundamental interactions by studying the anomalous isotopic abundance of Sm observed at the remnants of the natural reactors which were in operation at Oklo about 2 billion years ago, in terms of a possible deviation of the resonance energy from the value observed today. We rely on new samples that were carefully collected to minimize natural contamination and also on a careful temperature estimate of the reactors. We obtain the upper bound (−0.2±0.8)×10 −17 y −1 on the fractional rate of change of the electromagnetic as well as the strong interaction coupling constants. Our result basically agrees with and even suggests some improvement of the result due recently to Damour and Dyson. Strictly speaking, however, we find another choice of the resonance energy shift indicating a non-zero time variation of the constants. However, we find a rather strong but still tentative indication that this non-null range can be ruled out by including Gd data, for which it is essential to take the effect of contamination into account.

Neutron Activation Analysis of a Particle Returned from Asteroid Itokawa

Laboratory analysis of samples returned from an asteroid establishes a direct link between asteroids and meteorites and provides clues to the complex history of the asteroid and its surface. A single grain (~3 micrograms) returned by the Hayabusa spacecraft was analyzed by neutron activation analysis. This grain is mainly composed of olivine with minor amounts of plagioclase, troilite, and metal. Our results establish that the Itokawa sample has similar chemical characteristics (iron/scandium and nickel/cobalt ratios) to chondrites, confirming that this grain is extraterrestrial in origin and has primitive chemical compositions. Estimated iridium/nickel and iridium/cobalt ratios for metal in the Itokawa samples are about five times lower than CI carbonaceous chondrite values. A similar depletion of iridium was observed in chondrule metals of ordinary chondrites. These metals must have condensed from the nebular where refractory siderophile elements already condensed and were segregated.

First retrieval of hourly atmospheric radionuclides just after the Fukushima accident by analyzing filter-tapes of operational air pollution monitoring stations

No observed data have been found in the Fukushima Prefecture (FP) for the time-series of atmospheric radionuclides concentrations just after the Fukushima Daiichi Nuclear Power Plant (FD1NPP) accident. Accordingly, current estimates of internal radiation doses from inhalation, and atmospheric radionuclide concentrations by atmospheric transport models are highly uncertain. Here, we present a new method for retrieving the hourly atmospheric 137Cs concentrations by measuring the radioactivity of suspended particulate matter (SPM) collected on filter tapes in SPM monitors which were operated even after the accident. This new dataset focused on the period of March 12–23, 2011 just after the accident, when massive radioactive materials were released from the FD1NPP to the atmosphere. Overall, 40 sites of the more than 400 sites in the air quality monitoring stations in eastern Japan were studied. For the first time, we show the spatio-temporal variation of atmospheric 137Cs concentrations in the FP and the Tokyo Metropolitan Area (TMA) located more than 170 km southwest of the FD1NPP. The comprehensive dataset revealed how the polluted air masses were transported to the FP and TMA, and can be used to re-evaluate internal exposure, time-series radionuclides release rates, and atmospheric transport models.

Prompt gamma-ray analysis (PGA) of meteorite samples, with emphasis on the determination of Si

Neutron-induced prompt gamma-ray analysis (PGA) was applied to seven meteorite samples (Allende, Zagami, Acfer 209, ALH77005, ALH84001, EET79001 and Neagari). Samples were irradiated in both the thermal neutron and the cold neutron guided beams of JRR-3M at JAERI. Multiple samples of an Allende standard powder were analyzed for Si using two different methods: (1) the comparison method, using a Si standard, and (2) the mono-standard method, using Fe as an internal reference element. The Si concentrations determined by these two methods are in good agreement with literature values. The analytical sensitivity for Si using the cold neutron guided beam is∼14.3× higher than that for the thermal neutron guided beam. Other elements determined (B, Ca, Ti and S) also showed higher sensitivities using the cold neutron beam. The other meteorites studied showed some anomalous B and S values likely due to the effects of terrestrial weathering/contamination.

Hexafluoro complex of rutherfordium in mixed HF/HNO3 solutions

Summary Formation of anionic fluoride-complexes of element 104, rutherfordium, produced in the 248Cm(18O,5n) 261Rf reaction was studied by anion-exchange on an atom-at-a-time scale. It was found that the hexafluoro complex of Rf, [RfF6]2−, was formed in the studied fluoride ion concentrations of 0.0005–0.013 M. Formation of [RfF6]2− was significantly different from that of the homologues Zr and Hf, [ZrF6]2− and [HfF6]2−; the evaluated formation constant of [RfF6]2− is at least one-order of magnitude smaller than those of [ZrF6]2− and [HfF6]2−.

Extraction behavior of rutherfordium into tributylphosphate from hydrochloric acid

The extraction behavior of rutherfordium (Rf) into tributylphosphate (TBP) from hydrochloric acid (HCl) has been studied together with those of the lighter group-4 elements Zr and Hf. The extractability of 261Rf, 169Hf, and 85Zr into TBP was investigated under identical conditions in 7.2–8.0 M HCl by on-line reversed-phase extraction chromatography. The percent extractions of Rf, Hf, and Zr into the TBP resin increase steeply with increasing HCl concentration, and the order of extraction is Zr > Hf ≈ Rf. By considering the order of chloride complexation among these elements, it is suggested that the stability of the TBP complex of Rf tetrachloride is lower than those of Zr and Hf.

How Effectively is the Photon Activation Analysis Applied to Meteorite Samples

Chondritic meteorite samples were analyzed nondestructively by photon activation analysis. Powdered samples weighing about 50 mg each were irradiated with photons (γ-rays) converted from electrons accelerated by a linear electron accelerator at 20 and 30 MeV. With 30-minute and 6-hour irradiations, 11 and 12 elements with duplication of 6 elements could be determined, respectively. Considering that several major elements including Mg, Si and Fe can be determined in addition to Ti, Rb, Sr, Y and Zr, which cannot or hardly be determined by instrumental neutron activation analysis (INAA) with rather high sensitivity, instrumental photon activation analysis is as effective as INAA.

Adsorption of Db and its homologues Nb and Ta, and the pseudo-homologue Pa on anion-exchange resin in HF solution

Abstract Anion-exchange chromatography of element 105, dubnium (Db), produced in the 248Cm( 19F, 5n) 262Db reaction is investigated together with the homologues Nb and Ta, and the pseudo-homologue Pa in 13.9 M hydrofluoric acid (HF) solution. The distribution coefficient (Kd) of Db on an anion-exchange resin is successfully determined by running cycles of 1702 chromatographic column separations. The result clearly indicates that the adsorption of Db on the resin is significantly different from that of the homologues and that the adsorption of anionic fluoro complexes of these elements decreases in the sequence of Ta≈ Nb>Db≥Pa.

{alpha} decay of {sup 238}Cm and the new isotope {sup 237}Cm

Alpha decays of {sup 237}Cm and {sup 238}Cm have been studied using a gas-jet coupled on-line isotope separator. The new isotope {sup 237}Cm has been identified through the detection of 6656{+-}10 keV {alpha} particles. The {alpha} energy of {sup 238}Cm has been revised more precisely than the previous one. The {alpha} transition to the first excited 2{sup +} state in {sup 234}Pu has also been observed. It was found that the 2{sup +} energy in {sup 234}Pu is much higher than those in heavier Pu isotopes.

Performance of the multiple target He/PbI2 aerosol jet system for mass separation of neutron-deficient actinide isotopes

Abstract A multiple target He/PbI2 aerosol jet system coupled with a thermal ion source was installed in the isotope separator on line (JAERI-ISOL) at the JAERI tandem accelerator facility. The neutron-deficient americium and curium isotopes produced in the 233,235 U( 6 Li, xn) and 237 Np( 6 Li, xn) reactions were successfully mass-separated and the overall efficiency including the ionization of Am atoms was evaluated to be 0.3–0.4%. The identification of a new isotope 237 Cm with the present system is reported.