Nucleosynthesis of heavy elements in metal-deficient stars and the neutron capture reaction study

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Recently, the nucleosynthetic yields of massive stars of solar metallicity have been calculated from the onset of central hydrogen burning through explosions as Type II supernovae by Rauscher et al.. According to the calculation, the yields from Ni isotopes and Sr isotopes are overproduced by about 30. This overproduction factor is compared to the general overproduction of 10. Hence, the yields of former isotopes are overproduced by a factor three. This problem of overproduction has been one of the problems remaining in such calculations of the slow process nucleosynthetic yields. The origin of the overproduction is considered to be due to the uncertainty of the neutron capture cross section of nuclei relevant to the nucleosynthesis. In the present study we aimed at measuring the neutron capture cross section of ^<62>Ni in the resonance energy region of 4.5 keV by developing an experimental method. We succeeded to accurately determine the cross section, and thus the overproduction mentioned above turned out to be the uncertainty of the cross section used in the nucleosynthetic calculations.The neutron capture cross section of ^<18>O has been also measured at thermal and keV energies to study a possible influence of ^<18>O as a neutron poison. In this study, we found for the first time that the thermal capture reaction proceeded via a neutron capture by the two-hole four-particle configuration of ^<18>O. This finding would affect considerably in the neutron capture process both at thermal and keV energies.