Seiichi Shibata

Thermodynamics of reductive extraction of actinides and lanthanides from molten chloride salt into liquid metal

For the development of a pyrochemical group-partitioning process of actinides and lanthanides, the equilibrium distributions of these elements were measured in some typical binary phase systems of molten salt and liquid metal. A LiCl-KCl mixture was selected as the salt phase, and Zn and Bi were examined as the metal phase. Generally speaking, actinides were more reducible and extractable from the salt phase into the metal phase than lanthanides, and the group partitioning of these elements was feasible in these systems. However, the separation factors which were the ratios in the distribution coefficient between actinides and lanthanides were found to be different in different systems due to different alloying energies. The thermodynamic quantities of actinides and lanthanides were evaluated from the equilibrium distributions and discussed in some detail.

Target-dependence of light fragment production in photonuclear reactions at intermediate energies

Yields of 7Be, 10Be, 22Na, 24Na and 28Mg produced from natB, natC, natO, 23Na, 27Al, natSi, natS, natCl, natK, natCa, natV, 55Mn, natFe, 59Co, natNi, natCu, 89Y, natAg, natIn, 141Pr, 159Tb, 165Ho and 197Au in irradiations with bremsstrahlung having maximum end-point energies up to 1200 MeV were measured by γ-ray spectrometry (7Be, 22Na, 24Na and 28Mg) and accelerator mass spectrometry (10Be). The yields of heavier fragments, 39Cl, 43, 44m, 44g, 46, 47, 48Sc, 59Fe, and 56, 57, 58, 60Co, were also measured by γ-ray spectrometry in order to survey the relative contribution of fragmentation to spallation and/or fission in the mass yield curves. A distinct difference of the target mass-dependence of these yields has made it possible to disentangle the contributions of photospallation and photofragmentation processes. It was found that the neutron-to-proton ratios of targets strongly affect the formation of the nuclei by fragmentation as revealed in the yields of the isotopic pairs as well as of the single isotopes. The photon results were compared with those of proton-induced reactions, and no clear effect due to the difference of the initial interactions of photons and protons with nuclei was found in the fragment yields.

YIELD MEASUREMENTS OF 7BE AND 10BE PRODUCED BY PHOTONUCLEAR REACTIONS AT INTERMEDIATE ENERGIES : INTERCOMPARISON OF FRAGMENTATION PROCESSES BETWEEN PH OTON- AND PROTON-INDUCED REACTIONS

The yields of Be and Be produced by the interaction of bremsstrahlung with maximum end-point energies of 2501050 MeV with O, AI, Gl, Co, Cu, Y, Ag and Au targets were measured by gamma-ray spectrometry for Be and accelerator mass spectrometry for Be. For each target nuclide, the obtained yield (nb/equivalent quanta) was converted into the mean cross section (nb) using a simple 1/E spectrum approximation. The ^Be and Be production process in photonuclear reactions at several hundred MeV is discussed in comparison with that in proton-induced reactions at E^ = 0.8 —12GeV. Consequently, it is deduced that the Be and Be yields from the fragmentation process in the photo-reaction are relatively lower than those in the proton-induced reaction in the energy region studied in this work.

Recoil properties of radionuclides formed in photospallation reactions on complex nuclei at intermediate energies

The recoil properties of 14, 24, 26, 31, 21 and 20 radionuclides formed in photospallation reactions on natV, natCu, 93Nb, natAg, natTa, and 197Au, respectively, induced by bremsstrahlung of end-point energies (E0) from 600 to 1100 MeV, have been investigated using the thick-target thick-catcher method based on the two-step vector model. The measured forward-to-backward ratios (F/B) were found to be independent of the mass difference (ΔA) between a product (Ap) and a target (At) and also of At. The recoil velocities ν from the first step and the mean kinetic energies T of the residual nuclei in the second step were deduced and discussed by comparing with the reported results on proton-induced reactions. A comparison with T values calculated by the PICA (Photon-Induced Intranuclear Cascade Analysis) code at E0 = 400 MeV was also performed. It was found that although the code well reproduces the experimental results of natV and natCu, the same calculation for heavier targets gives T values lower than the experimental results, indicating some nuclear-structure effect, such as a medium effect notably at At ≥ 100. The parameter values of εs = T/(ΔA/At), the average kinetic energy of the emitted particles in a random-walk process of both the photon- and proton-reactions, were found to increase along with an increase of At, but change slopes to become constant above At = 100.

A method to detect low-level 63Ni activity for estimating fast neutron fluence from the Hiroshima atomic bomb

The Hiroshima and Nagasaki atomic bombs resulted in the worst reported exposure of radiation to the human body. The data of survivors have provided the basis for the risk estimation for ionizing radiation, and thus are widely used as the basis of radiation safety. In this report we have studied a new method to detect the low-level 63Ni activity in copper samples in order to estimate the fast neutron fluence from the Hiroshima atomic bomb. Only 0.8 x 10(-3) Bq g(-1) of 63Ni is expected to be produced by the atomic bomb in a copper sample with the 63Cu(n, p)63Ni reaction at a distance of 500 m from the hypocenter. Our method has the required level of sensitivity for determination of the fast neutron fluence out to distances of at least 500 m, and perhaps as far as 1,000 m. We have already investigated and collected some bomb-irradiated copper samples for further study.

Measurements of the Production Cross Sections of Tritium from Oxygen Using p-Be and p-Li Neutrons up to En = 38 MeV

The production cross sections of tritium from oxygen have been measured in p-Be and p-Li neutron fields installed at the sectorfocusing (SF) cyclotron of the Institute for Nuclear Study (INS), University of Tokyo. Irradiations were performed with the semi-monoenergetic neutrons produced from the Be(p,n)B reaction at proton energies from 20 up to 40 MeV in 2.5-MeV steps, and those from Li(p,n)Be in 5-MeV steps with proton intensities of 2—5 μΑ, which yields neutron flux densities from 10 to 10 n/cm/sec at the position of sample irradiation. The neutron energy spectra were determined by an NE-213 scintillation counter. The tritium produced in the water used as the oxygen target was extracted by a distillation method, and measured by a liquid scintillation counter. The excitation functions for the 0(n,t)N reaction, measured by the p-Be and p-Li neutrons, agreed well with each other within the experimental uncertainties. The obtained results have been compared with the general trend in the (n,t) cross sections as a function of the atomic number of the target appearing in the literature.

Yields and Recoil Properties of Products from the Interaction of Natural Copper with Intermediate-Energy 14N, 15N and 40Ar Ions

Reaction residues in the interaction of copper with intermediateenergy N, 1 N and 4 Ar ions (26 to 135 MeV/u) have been studied using non-destructive y-ray spectrometry. Formation cross-sections and average forward ranges were measured for 58 products. The data were used to obtain the mass yield distribution and the longitudinal momentum transfer. The results are compared with those from the studies reported on the interaction of copper with heavy projectiles, and discussed in terms of the transition of the reaction mechanism from low energy to relativistic energy.

Excitation function for 63Cu(n,p)63Ni reaction in neutron energy range up to 15 MeV

The excitation function for the (63)Cu(n,p)(63)Ni reaction has been measured by activation method using the 4.5 MV Dynamitron accelerator of the Fast Neutron Laboratory of Tohoku University. Copper plates and hollow spherical copper shells were irradiated by neutrons of various energy up to 14.9 MeV produced by the T(p,n), D(d,n), and T(d,n) reactions. The (63)Ni produced in the irradiated copper target was chemically separated. The beta-rays emitted from the extracted (63)Ni were measured by a liquid scintillation method. The cross sections obtained were compared with the evaluated data files of JENDL-3.3, ENDF/B-VI and FENDL/A-2.0. Consequently, it is found that FENDL/A-2.0 is consistent with our experimental data in the energy range studied in this work. The effect of proton shell appeared in the excitation function obtained is also discussed.

Recoil Study of 27Al(γ,2pn)24Na Reaction at Intermediate Energies

Division of Physical Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa-shi, Ishikawa 920-1192, Japan ^ Department of Chemistry, Faculty of Science, Kanazawa University, Kanazawa-shi, Ishikawa 920-1192, Japan ^ Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Hachioji-shi, Tokyo 192-0397, Japan Research Reactor Institute, Kyoto University, Sennan-gun, Osaka 590-0494, Japan Faculty of Environmental and Information Sciences, Yokkaichi University, Yokkaichi-shi, Mie 512-8512, Japan * Department of Economics, Faculty of Economics, Otemon-Gakuin University, Ibaraki-shi, Osaka 567-8502, Japan

Equilibrium distributions of trivalent actinides and lanthanides in the liquid–liquid extraction system of TBP and molten Ca(NO3)2·4H2O

Abstract The extraction distributions of Am, Cm and lanthanides between tri-butyl phosphate solution and molten calcium nitrate tetrahydrate (Ca(NO 3 ) 2 ·4H 2 O) were studied radiochemically. The apparent equilibrium constants of the extraction reaction were determined and their systematics along the series was studied. By comparing the observed systematics with those obtained for other similar extraction systems it was found that there is a large difference in hydration effect between the lighter and heavier f-series in water-deficient hydrate melt systems.