Mizunami Underground Research Laboratory Project, Annual report for fiscal year 2011

Kunimaru, Takanori; Mikake, Shinichiro; Nishio, Kazuhisa; Tsuruta, Tadahiko; Matsuoka, Toshiyuki; Ishibashi, Masayuki; Sasao, Eiji; Hikima, Ryoichi; Tanno, Takeo; Sanada, Hiroyuki; et al.

JAEA-Review 2013-018, 169 Pages, 2013/09

JAEA-Review-2013-018.pdf:15.71MB

Japan Atomic Energy Agency (JAEA) at Tono Geoscience Center (TGC) is pursuing a geoscientific research and development project namely the Mizunami Underground Research Laboratory (MIU) Project in crystalline rock environment in order to construct scientific and technological basis for geological disposal of High-level Radioactive Waste (HLW). The MIU Project has three overlapping phases: Surface-based Investigation phase (Phase I), Construction phase (Phase II), and Operation phase (Phase III). The MIU Project has been ongoing the Phase II and the Phase III in 2011 fiscal year. This report shows the results of the investigation, construction and collaboration studies in fiscal year 2011, as a part of the Phase II and Phase III based on the MIU Master Plan updated in 2010.

Barrier distributions derived from quasielastic backscattering of Ti, Cr, Fe, Ni, and Zn projectiles on a Pb target

Mitsuoka, Shinichi; Ikezoe, Hiroshi; Nishio, Katsuhisa; Tsuruta, Kaoru*; Jeong, S.-C.*; Watanabe, Yutaka*

Physical Review Letters, 99(18), p.182701_1 - 182701_4, 2007/11

https://doi.org/10.1103/PhysRevLett.99.182701

In order to study the nucleus-nucleus interaction in Pb-based cold fusion, we have measured excitation functions for quasi-elastic scattering of Ti, Cr, Fe, Ni and Zn projectiles on Pb target at backward angles of nearly 180. Coulomb barrier distributions were extracted from the first derivative of measured quasi-elastic scattering cross sections relative to the Rutherford scattering cross section. The mean values of the barrier distributions always shift toward the low energy side about 4-6 MeV compared with the Bass barrier height. The shape of the barrier distributions are well reproduced by the results of a coupled-channels calculation taking account of the coupling effects of two phonon excitations of the quadrupole vibration for the projectiles and three phonon excitations of the octupole vibration for the Pb target.

Measurement of evaporation residue cross-sections of the reaction Si + U at subbarrier energies

Nishio, Katsuhisa; Hofmann, S.*; Heberger, F. P.*; Ackermann, D.*; Antalic, S.*; Comas, V. F.*; Gan, Z.*; Heinz, S.*; Heredia, J. A.*; Ikezoe, Hiroshi; et al.

AIP Conference Proceedings 891, p.71 - 79, 2007/03

https://doi.org/10.1063/1.2713502

Seaborgium isotopes were produced in the fusion reaction Si + U as evaporation residues (ERs), and the cross sections were determined. The experiment was carried out at GSI in Darmstadt, Germany. At the center-of-mass energy of E= 144 MeV, three decay chains starting from Sg were observed, and the corresponding ER cross section was determined to be 67 pb. At the sub-barrier energy of E= 133 MeV, three spontaneous fission events of a new isotope Sg were detected. The cross section was 10 pb. The half-life of Sg was determined to be 120 ms. The ER cross sections were compared with a statistical model calculation. In the fusion process, the coupled channel calculation taking into account the prolate deformation of U was adopted to determine the capture cross section. The calculated capture cross section agrees well with the fission cross section of Si + U obtained at the JAEA tandem accelerator. The measured cross section of Sg at the sub-barrier energy is factor 10 larger than the calculation based on the one-dimensional model in the fusion process, showing the fusion enhancement caused by the deformation of U. However, disagreement with the calculation suggests the presence of quasi-fission channel. At the above barrier energy of E = 144 MeV, the measured cross section is well reproduced by the calculation. This means that the interaction of Si at the equotorial side of U has advantage on the fusion process.

Evidence of complete fusion in the sub-barrier O+U reaction

Nishio, Katsuhisa; Ikezoe, Hiroshi; Nagame, Yuichiro; Asai, Masato; Tsukada, Kazuaki; Mitsuoka, Shinichi; Tsuruta, Kaoru; Sato, Kenichiro; Lin, C. J.; Osawa, Takaaki*

Physical Review Letters, 93(16), p.162701_1 - 162701_4, 2004/10

https://doi.org/10.1103/PhysRevLett.93.162701

The fission fragment angular distributions for reactions using actinide targets such as O+U show anomalously large anisotropy than the prediction of the transition state model. To interprete this phenomenon, the orientation dependent quasi-fission model was proposed. As the U has prolate deformation, the interaction of O with the U in the sub-barrier region is restricted to the tip collisions. Hinde et al. interpreted that the anomalously large angular anisotropy is due to the quasi-fission, that is the complete fusion is not achieved in the sub-barrier region. The presence (or absence) of the complete fision is found by measuring the evaporation residue cross sections. We measured the evaporation residue cross sections for O+U by using the O beams supplied by the JAERI-tandem accelerator. As a result, complete fusion was observed in the sub-barrier region and no significant fusion hindrace was observed.

Measurement of fusion barrier distribution for cold fusion reactions

Mitsuoka, Shinichi; Ikezoe, Hiroshi; Nishio, Katsuhisa; Tsuruta, Kaoru; Jeong, S.-C.*; Watanabe, Yutaka*

no journal, , 

no abstracts in English