N. Yoshikawa

The KEK–JAERI joint RNB project

A new ISOL-based radioactive nuclear beam (RNB) facility has been constructed as a joint project of the High Energy Accelerator Research Organization (KEK) and the Japan Atomic Energy Research Institute (JAERI) at the Tandem accelerator of the Tokai site of JAERI. It uses heavy-ion linacs and related equipment of the presently closed KEK-RNB facility. Fission fragments with energy from 0.1 to 8 MeV/u will be available at this facility.

Direct measurements of (α, n) and (p, n) reaction cross sections using light neutron-rich radioactive nuclear beams

Abstract A project to acquire directly nuclear cross sections of (α, n) and (p, n) reactions using low energy light neutron-rich radioactive nuclear beams (RNB) is in progress at JAERI-Tandem facility. The method of the production of neutron-rich RNB, an improvement of a gas counter (MSTPC) in order to work effectively under the high RNB-injection rate, and the feasibility of our experiments are discussed.

Ion source development for isotope separator on-line based radioactive nuclear beam facility at KEK-Tanashi

For an isotope separator on-line based radioactive nuclear beam facility at KEK-Tanashi, two different types of ion sources are currently employed: a single stage 6.4 GHz electron cyclotron resonance ion source for 18Ne2+ and 19Ne2+ ions and a surface ionization-type ion source for 8Li1+ ions. The production target for Ne radioisotopes is LiF powder. Enclosed in a water-cooled Cu target cell, the target can sustain proton beam power of 120 W for a long term. The methods to suppress unwanted isotopes, like 19F in 19Ne and 18O in 18Ne, are discussed. For the production of 8Li1+ with the surface ionization-type ion source, a recoil-catcher method is adopted. The feasibility is discussed, comparing to a thick target method.

Measurement of the 16N(α, n) reaction cross section

Abstract In order to study the starting point of the r-process, the 16 N(α, n) cross section has been measured directly at the energy region of E cm = 1.5 – 4.0 MeV, corresponding to the Gamow peak energy T 9 = 2 – 6.

A Systematic Study of Astrophysical Reaction Rates through 8Li

Excitation functions of 8Li(α,n), (d, t) and 12B(α,n) reactions were directly measured in the energy region of astrophysical interest using low‐energy radioactive nuclear beams of 8Li and 12B. Each measured excitation function is strongly affected by one or more resonances through a compound nucleus. The measured excitation functions are presented. Dominant r‐process paths through 8Li at various temperatures are discussed and our future experimental plan is also presented.

A New Measurement of the 8Li(α,n)11B Reaction for Astrophysical Interest

The 8Li(α,n)11B reaction has been measured directly and exclusively in the energy region of Ecm=0.45–1.75 MeV by using highly efficient detector system covering Ecm= 0.56 MeV, which corresponds to the Gamow window at T9=1. This experiment has been performed in the condition of inverse kinematics by using low‐energy radioactive 8Li beam at the Tandem accelerator facility of Japan Atomic Energy Research Institute. The reaction cross section obtained in the present measurement is consistent with that of the previous exclusive measurements within the errors in an overlapping energy region, but is less than half of that of the inclusive measurements, in particular for lower energy region.

Study of astrophysical (α, n) reactions using light‐neutron rich radioactive nuclear beams

A systematic study of astrophysical reaction rates of (α, n) reactions on light neutron‐rich nuclei using low‐energy radioactive nuclear beams is in progress at the tandem facility of Japan Atomic Energy Agency. Exclusive measurements of 8Li(α, n)11B and 12B(α, n)15N reaction cross sections have been performed successfully. Their excitation functions together with the experimental method are presented.

Direct measurement of 8Li+d reactions of astrophysical interest

The excitation functions of the 8Li(d,t)7Li and the 8Li(d,p)9Li reactions were directly measured using 8Li beams with Ecm = 0.3, 0.4, 0.5, 0.7, 0.8, 1.0, 1.1, and 1.2 MeV irradiating CD2 targets. These beam energies covered the Gamow peaks for 1−3×109 K. Large cross sections were observed at around Ecm = 0.8 MeV for the 8Li(d,t)7Li and Ecm = 1.0 MeV for the 8Li(d,p)9Li, implying the existence of a resonant state of 10Be at the excitation energy of around 22.4 MeV. Enhanced with the present work, the astrophysical reaction rates of the 8Li(d,t)7Li and the 8Li(d,p)9Li reactions are higher by one and two orders of magnitude than the previously evaluated ones, respectively.

Study of Astrophysical (α, n) and (p, n) Reactions on Light Neutron‐Rich Nuclei by Means of Low‐Energy RNB

A systematic study of astrophysical reaction rates of (α, n) and (p, n) reactions on light neutron‐rich nuclei by using low‐energy radioactive nuclear beam is in progress at the tandem facility of Japan Atomic Energy Research Institute. Exclusive measurements of 8Li(α, n)11B and 16N(α, n)19F reaction cross sections have been performed successfully. Their excitation functions together with the experimental method are presented.

A recoil mass separator for nuclear astrophysics experiments

Abstract A recoil mass separator was constructed for experiments of nuclear astrophysics using radioactive nuclear beams, and its performance was tested. The observed beam suppression factor around M ∼20 was 10 −4 when the system was tuned for ΔM =1 heavier ions than beam ions. With a charge state breeding technique, it became 10 −8 when the system was tuned for Δq =+1 larger ions than beam ions.