I. Nishinaka

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.

Oxidation of Element 102, Nobelium, with Flow Electrolytic Column Chromatography on an Atom-at-a-Time Scale

We report here on the successful oxidation of element 102, nobelium (No), on an atom-at-a-time scale in 0.1 M alpha-hydroxyisobutyric acid (alpha-HIB) solution using a newly developed technique, flow electrolytic column chromatography. It is found that the most stable ion, No(2+), is oxidized to No(3+) within 3 min and that the oxidized No complex with alpha-HIB holds the trivalent state in the column above an applied potential of 1.0 V.

The 95Zr(n, γ)96Zr Cross Section from the Surrogate Ratio Method and Its Effect on s-process Nucleosynthesis

The 95Zr(n,gamma)96Zr reaction cross section is crucial in the modelling of s-process nucleosynthesis in asymptotic giant branch stars because it controls the operation of the branching point at the unstable 95Zr and the subsequent production of 96Zr. We have carried out the measurement of the 94Zr(18O,16O) and 90Zr(18O,16O) reactions and obtained the gamma-decay probability ratio of 96Zr* and 92Zr* to determine the 95Zr(n,gamma)96Zr reaction cross sections with the surrogate ratio method. Our deduced maxwellian-averaged cross section of 66+-16 mb at 30 keV is close to the value recommended by Bao et al. (2000), but 30% and more than a factor of two larger than the values proposed by Toukan & Kappeler (1990) and Lugaro et al. (2014), respectively, and routinely used in s-process models. We tested the new rate in stellar models with masses between 2 and 6 Msun and metallicities 0.014 and 0.03. The largest changes - up 80% variations in 96Zr - are seen in models of mass 3-4 Msun, where the 22Ne neutron source is mildly activated. The new rate can still provide a match to data from meteoritic stardust silicon carbide grains, provided the maximum mass of the parent stars is below 4 Msun, for a metallicity of 0.03.

Measurement of neutron capture cross section of Li-7 at J-PARC / MLF / ANNRI

We have measured the 7Li(n,γ)8Li reaction at Accurate Neutron-Nucleus Reaction Measurement Instrument (ANNRI) installed at the Material and Life science experimental Facility in the Japan Proton Accelerator Research Complex (J-PARC / MLF). In this experiment, we used intense pulsed neutron beam provided by J-PARC / MLF and high performance Ge spectrometer, which is one of the main detectors of the ANNRI. We clearly detected γ rays from the 7Li(n,γ)8Li reaction with sufficient signal-to-noise ratio.

Measurement of the 12C(α,γ)16O reaction at TRIAC

We have measured the γ-ray angular distribution of the 12C(α,γ)16O reaction at TRIAC (Tokai Radioactive Ion Accelerator Complex) to accurately determine the E1 and E2 cross sections. In this experiment, we used high efficiency anti-Compton NaI(T1) spectrometers to detect a γ-ray from the reaction with large S/N ratio, intense pulsed α-beams to discriminate true event from background events due to neutrons from 13C(α,n)16O reaction with a time-of-flight (TOF) method. We succeeded in removing a background events due to neutrons and clearly detected γ-ray from the 12C(αγ)16O reaction with high statistics.

Effects of nuclear orientation on fusion and fission process for reactions using actinide target nuclei

Fission fragment mass distributions in the reaction of 30Si+238U were measured at the energies around the Coulomb barrier. At the above‐barrier energies, the mass distribution showed Gaussian shape. At the sub‐barrier energies, triple‐humped distribution was observed, which consists of symmetric fission and asymmetric fission peaked at AL/AH≈90/178. The asymmetric fission should be attributed to quasifission from the results of the measured evaporation residue (ER) cross‐sections produced by 30Si+238U. The cross‐section for 263Sg at the above‐barrier energy agree with the statistical model calculation which assumes that the measured fission cross‐sections are equal to the fusion cross‐sections, whereas the one for 264Sg measured at the sub‐barrier energy is smaller than the calculation, indicating the presence for quasifission. We also report the results on the fragment mass distributions for 36,34S+238U and 40Ar+238U.

Effects of nuclear orientation on fusion and fission process in heavy ion reactions

Effects of nuclear orientation on fission fragment mass distributions in the reaction of 30Si+238U were investigated. The mass distributions showed a Gaussian shape in the above barrier region, having a character of fusion‐fission. At the sub‐barrier energies, the asymmetric fission component around AL/AH≈90/178 appears, representing quasifision. The measured evaporation residue cross sections for 30Si+238U in [1] have also suggested the competition between fusion and quasifission at sub‐barrier region, whereas the fusion is the main process in the above barrier region. These results suggest an influence of orientation effects of the deformed target nuclei on the reaction. Discussion will be given on the difference in the mass distributions between 30Si+238U and 36S+238U.

Nuclear‐Charge Polarization at Scission in Proton‐Induced Fission of Light Actinides

Fragment mass yields and the average neutron multiplicity in the proton‐induced fission of 232Th and 233U were measured by a double time‐of‐flight method. The most probable charges of secondary fragments were evaluated from the fragment mass yields measured and the fractional cumulative yields reported. The nuclear charge polarization of primary fragments at scission was obtained by correcting the most probable charge of secondary fragments for neutron evaporation. The results show that the nuclear‐charge polarization at scission is associated with the liquid‐drop properties of nuclei and the proton shell effect with Z = 50 of heavy fragments and that it is practically insensitive to mass and excitation energy of the fissioning nucleus in the region of light actinides.

Effects of nuclear orientation on fission fragment mass distributions in the reactions of 34,36S+238U

Fission fragment mass distributions in the reactions of 34,36S+238U were measured at bombarding energies around the Coulomb barrier. The data showed a transition from symmetric to asymmetric mass distributions when the beam energies were decreased from the above‐barrier to sub‐barrier values. The asymmetric fission is attributed to quasifission of the reacting system at polar collisions, whereas the symmetric fission originates from the compound nucleus produced in equatorial collisions. The results suggest a influence of orientation effects of the deformed target nuclei on fusion.

Effects of nuclear orientation on fission fragment mass distributions in the reactions using actinide target nuclei

Effects of nuclear orientation on fission fragment mass distributions in the reactions of 30Si36,34S+238U were investigated. In the reactions for 30Si+238U, the mass distributions showed a Gaussian shape in the above barrier region, having a character of fusion‐fission. At the sub‐barrier energies, the asymmetric fission component around AL/AH≈90/178 appears. The asymmetric fission is attributed to quasifission. Strong variation of the mass distributions with energy is observed for the reactions of 36,34S+238U. The results suggested the competition between fusion and quasifission, resulting from the orientation effects of the deformed target nuclei on the reaction.