A. Tomyo

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.

New Approach for Measuring the (n,γ) Cross Section of a Nucleus by a Few keV Neutron

We have for the first time determined with high precision the energy spectrum of low-energy neutrons ( E n <10 keV) which are produced in the 7 Li( p , n ) 7 Be reaction, by detecting γ-rays of the 197 Au( n ,γ) 198 Au reaction whose cross section is known. An anti-Compton NaI(Tl) spectrometer played an essential role in detecting the γ-rays with a good signal to noise ratio by discriminating large background due to thermalized neutrons in the measurement room. The low energy neutrons thus derived were successfully used to measure the 62 Ni( n ,γ) 63 Ni reaction cross section. The present low energy neutrons could be extensively used for cross section measurements for neutron capture reactions and elastic scatterings from nuclei of nuclear astrophysical interests.

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.

Probing universe with fast neutrons

Fast neutrons play crucial roles as a probe to trace the history of the universe. The present paper describes our recent work on the measurement of the neutron capture and neutron inelastic scattering cross sections of various nuclei from primordial and stellar nucleostyntheses point of view, which have been carried out by developing a high sensitive measurement system. The obtained results are compared to previous works and theoretical calculations.

Li7(n,γ)Li8reaction and theS17factor atEc.m.>500keV

The partial cross sections from the neutron capture state to the ground and first excited states in {sup 8}Li have been separately determined for the first time at stellar neutron energy. The direct and weak cascade {gamma} rays from the capture and first excited states to the ground state were measured by means of anti-Compton NaI(Tl) and anti-Compton HPGe spectrometers, respectively. The {gamma}-ray branching ratio and the cross sections thus determined agree with that for thermal neutrons assuming a 1/v neutron velocity dependence. By comparing the cross sections with calculations based on the nonresonant direct capture mechanism it is shown that the cross sections are sensitive to the interaction potential of the incident neutron with the {sup 7}Li target nucleus. This analysis confirms the possibility of deriving the parameters necessary for the calculation of the astrophysical S factor S{sub 17}(E) for the {sup 7}Be(p,{gamma}){sup 8}B reaction in the upper energy range above 500 keV.

{sup 7}Li(n,{gamma}){sup 8}Li reaction and the S{sub 17} factor at E{sub c.m.}>500 keV

The partial cross sections from the neutron capture state to the ground and first excited states in {sup 8}Li have been separately determined for the first time at stellar neutron energy. The direct and weak cascade {gamma} rays from the capture and first excited states to the ground state were measured by means of anti-Compton NaI(Tl) and anti-Compton HPGe spectrometers, respectively. The {gamma}-ray branching ratio and the cross sections thus determined agree with that for thermal neutrons assuming a 1/v neutron velocity dependence. By comparing the cross sections with calculations based on the nonresonant direct capture mechanism it is shown that the cross sections are sensitive to the interaction potential of the incident neutron with the {sup 7}Li target nucleus. This analysis confirms the possibility of deriving the parameters necessary for the calculation of the astrophysical S factor S{sub 17}(E) for the {sup 7}Be(p,{gamma}){sup 8}B reaction in the upper energy range above 500 keV.

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.

Measurement of the p(n,γ)d reaction cross section between En = 100 and 350 keV

Abstract The measurement of p(n,γ)d reaction cross section has been performed at the neutron energies between 100 and 350 keV using the pulsed neutrons produced by the 7 Li(p,n) 7 Be reaction and detecting the prompt γ-ray from this reaction with an anti-Compton NaI(TI) spectrometer.

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.