T. Ohtsuki

Strongly enhanced DD fusion reaction in metals observed for keV D+ bombardment

The excitation functions of the yield of protons emitted in the D(d,p)T reaction in Ti, Fe, Pd, PdO and Au were measured for bombarding energies between 2.5 and 10 keV. It was found that the reacti...

Anomalous enhancement of DD reaction in Pd and Au/Pd/PdO heterostructure targets under low-energy deuteron bombardment

Yields of protons emitted in the D+D reaction in Pd, Au/Pd/PdO, Ti, and Au foils are measured by a dE-E counter telescope for bombarding energies between 2.5 and 10 keV. The experimental yields are compared with those predicted from a parametrization of the cross section and stopping power at higher energies. It is found that for Ti and Au target the enhancement of the D(d,p)T reaction is similar to that observed with a deuterium gas target (several tens of eV). The dependence of the yields on the bombarding energy corresponds well to the screening potential parameters Us=250±15 eV for Pd and 601 ±23 eV for Au/Pd/PdO. Possible models of the enhancement obtained are discussed.

Systematic study of foreign-atom-doped fullerenes by using a nuclear recoil method and their MD simulation

The formation of atom-doped fullerenes has been investigated by using several types of radionuclides produced by nuclear reactions. It was found that the endohedral fullerenes (Kr@C60,  Xe@C60) and their dimers, furthermore, heterofullerenes, such as AsC59, GeC59 and their dimers, are produced by a recoil process following nuclear reactions. Other nuclear reaction products (Na, Ca, Sc, etc.) may destroy most of the fullerene cage in the same process. Carrying out ab initio molecular-dynamics simulations based on an all-electron mixed-basis approach, we confirmed that the formation of Kr- (or Xe-) atom-doped endohedral fullerenes and of substitutional heterofullerenes doped with an As atom is really possible. The experimental and theoretical results indicate that the chemical nature of doping atoms is important in the formation of foreign-atom-doped fullerenes.

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.

Two-phonon giant resonances in 136 Xe, 208 Pb, and 238 U

The excitation of the double-phonon giant dipole resonance was observed in heavy projectile nuclei impinging on targets of high nuclear charge with energies of 500‐700 MeV/nucleon. New experimental data are presented for 136 Xe and 238 U together with further analysis of earlier data on 208 Pb. Differential cross sections ds/dE* and ds/du for electromagnetic excitations were deduced. Depending on the isotope, cross sections appear to be enhanced in comparison to those expected from a purely harmonic nuclear dipole response. The cumulative effect of excitations of two-phonon states composed of one dipole and one quadrupole phonon, of predicted anharmonicities in the double-phonon dipole response, and of damping of the dipole resonance during the collision may account for the discrepancy. In addition, decay properties of two-phonon resonances were studied and compared to that of a statistical decay.

Two deformation paths in proton-induced fission of 232Th☆

Abstract Velocities of complementary fission fragments have been accurately measured by a double velocity time-of-flight method in the proton-induced fission of 232 Th with incident energies from 12.0 to 14.7 MeV. The results experimentally demonstrate for the first time the correlation among the threshold energy, the total fragment kinetic energy, and the mass division mode in fission: one type of the fission process has a lower threshold energy and leads to a compact scission configuration with reflection asymmetry, and the other type has a higher threshold energy and leads to a symmetric elongated scission configuration.

Formation of dimer, trimer, and tetramer of C60 and C70 by γ-ray, charged-particle irradiation, and their HPLC separation

Abstract C60 and C70 fullerenes were irradiated by high-energy γ-rays and charged particles. Coalesced products of C60 and C70 have been isolated and detected in the liquid phase by a radiochromatographic technique. It was found that not only 11 C radioactive fullerene dimer, trimer, and possibly tetramer were produced by a recoil implantation process following nuclear reaction, but also such non-radioactive coalesced products were produced by the recombination process after ionization by γ-rays or charged particles.

Energetic Protons and α Particles Emitted in 150-keV Deuteron Bombardment on Deuterated Ti

Energetic charged particles have been measured in the bombardment of 150-keV deuterons on deuterated Ti. Protons and α particles were observed with energies up to ~17 and ~6.5 MeV, respectively, which can never be attained in the D+D reaction. A bump structure at around 14 MeV seen in the proton spectrum can be well explained as emitted in the sequential reaction involving three deuterons. However, protons and α particles distributed continuously up to the maximum energies can never be understood as products of the conceivable nuclear reactions.

Development of a rapid source preparation method for high-resolution α-particle spectrometry

In order to prepare sources of short-lived actinides for alpha-particle spectrometry, a coprecipitation method with Sm hydroxide was developed. The preparation procedure can be completed within 5 min with a high chemical yield of over 90%. It was found that the uniformity of the produced sources was sufficient to provide a high resolution of better than 20 keV. Under this method, we successfully measured the alpha-particle spectrum of short-lived Cf isotopes produced in the (238)U((12)C, xn) reaction.

Ab initio molecular dynamics in an all-electron mixed-basis approach: application to atomic insertions to C60

Among many ab initio methods, the all-electron mixed-basis approach using numerical atomic orbitals confined inside non-overlapping spheres as well as plane waves has an advantage in the application to molecular-dynamics simulations of systems composed of second-row and transition-metal elements. As an example, we apply this new approach to atomic insertions through a six-membered ring of C60. We show that a krypton atom can be more easily inserted into a C60 cage than a potassium or copper atom.