H. Makii

62Ni(n, γ)63Ni Reaction and Overproduction of Ni Isotopes

The neutron capture cross section of 62Ni has been measured in the energy range from 5.5 to 90 keV by employing a prompt discrete γ-ray detection method with the use of an anti-Compton NaI(Tl) spectrometer. The Maxwellian-averaged capture cross section at 30 keV is derived as being 37.0 ± 3.2 mbarn, 3 times larger than the value currently used for the nucleosynthetic yield estimations in massive stars. The result could provide crucial information for the long-standing problem of the largest overproduction of 62Ni. The intense discrete γ-ray feeding from a neutron capture state to the ground state of 63Ni was for the first time observed at stellar neutron energy. This observation and the neutron energy dependence of the total neutron capture cross section of 62Ni indicate clearly that the dominant capture process of 62Ni is a nonresonant direct s-wave capture process and not a p-wave capture process as previously predicted.

Neutron capture cross section measurement of 20,22Ne for stellar nucleosynthesis

Abstract We have measured the neutron capture cross sections of 20Ne(n,γ)21Ne and 22Ne(n,γ)23Ne at stellar energy by detecting a discrete γ-ray feeding from a neutron capturing state to a low-lying state. In this work the non-resonant direct p-wave capture reaction process has been identified for the first time in the keV neutron capture reactions of Ne isotopes.

Neutron-induced reactions using a {gamma}-ray detector in a {sup 12}C({alpha},{gamma}){sup 16}O reaction study

Neutron-induced background events occurring within a {gamma}-ray detector in the {sup 12}C({alpha},{gamma}){sup 16}O reaction study are discussed by comparing a spectrum taken by a NaI(Tl) detector with a pulsed {alpha} beam with that taken previously by a Ge detector using a continuous {alpha} beam. Both spectra contain such background events induced by neutrons from the ({alpha},n) reaction on {sup 13}C and/or {sup 9}Be contained in enriched {sup 12}C targets. These observations together with a calculated {gamma}-ray spectrum of the neutron-induced reaction by Ge isotopes indicate the thus-produced background events, which would barely be reduced by using shield materials, become significant background in the {sup 12}C({alpha},{gamma}){sup 16}O reaction study at low-{alpha}-beam energy.Neutron-induced background events occurring within a {gamma}-ray detector in the {sup 12}C({alpha},{gamma}){sup 16}O reaction study are discussed by comparing a spectrum taken by a NaI(Tl) detector with a pulsed {alpha} beam with that taken previously by a Ge detector using a continuous {alpha} beam. Both spectra contain such background events induced by neutrons from the ({alpha},n) reaction on {sup 13}C and/or {sup 9}Be contained in enriched {sup 12}C targets. These observations together with a calculated {gamma}-ray spectrum of the neutron-induced reaction by Ge isotopes indicate the thus-produced background events, which would barely be reduced by using shield materials, become significant background in the {sup 12}C({alpha},{gamma}){sup 16}O reaction study at low-{alpha}-beam energy.

Preparation for the 12C(α,γ)16O experiment using pulsed α beam

Abstract We have installed a new experiment system to measure the 12 C(α,γ) 16 O reaction cross section accurately below E cm = 1.75 MeV. Using the system, we will also measure the γ-angular distributions of reaction to determine the σ E2 σ E1 ratio with high accuracy.

84Kr(n,γ)85Kr reaction cross section measured by an NaI(T1) spectrometer between 10 and 80 keV

Abstract A discrete γ-ray emitted promptly from the 84 Kr(n,γ) 85 Kr reaction in the keV energy region has been detected for the first time and thereby the reaction cross section has been accurately determined. The obtained cross section is consistent with the previously accepted data.