Search

Resonant scattering with low-energy radioactive nuclear beams of E < 5 MeV/u have been studied at CRIB of CNS and at RIPS of RIKEN. As an extension to the present experimental technique, we will install an advanced polarized proton target for resonant scattering experiments. A Monte-Carlo simulation was performed to study the feasibility of future experiments with the polarized target. In the Monte-Carlo simulation, excitation functions and analyzing powers were calculated using a newly developed R-matrix calculation code. A project of a small-scale radioactive beam facility at Kyushu University is also briefly described.

We determined the total reaction rate of the {sup 11}C({alpha},p){sup 14}N reaction relevant to the nucleosynthesis in explosive hydrogen-burning stars. The measurement was performed by means of the thick target method in inverse kinematics with {sup 11}C RI beams. We performed the identification of the ground-state transition and excited-state transitions using time-of-flight information for the first time.

CRIB (CNS Radioactive Ion Beam separator) is a low-energy RI beam separator at the Center for Nuclear Study (CNS) of the University of Tokyo. Studies on proton and alpha resonance scatterings, (α, p) reactions, and other types of measurements (β-decay lifetimes etc.) have been performed using RI beams at CRIB, motivated by interests on astrophysical reactions and exotic nuclear structure. Among the studies at CRIB, the measurement of 7Li+α/7Be+α resonant scatterings are presented.

Several reactions have been experimentally studied, including the 12N(d,n)13O and the ones induced by the 3He+12C entrance channel. The former was carried out at the CRIB facility of University of Tokyo, aiming to indirectly determine the astrophysical reaction rates of the 12N(p,γ)13O reaction. For the 3He+12C entrance channel, many excited states of several nuclei are populated and the angular distribution of each state is being analyzed.

We determined the 11C(α,p)14N reaction rate relevant to the nucleosynthesis in explosive hydrogen-burning stars. The measurement was performed by means of the thick target method in inverse kinematics with 11C RI beams. We derived the excitation functions for the ground-state transition and excited-state transitions using time-of-flight information for the first time. The present reaction rate is compared to the previous one.

We performed an experiment of the 21Na(αp)24Mg reaction for the first time by a direct measurement with a thick target method. The studied energy was covered for high temperature conditions in X-ray bursts and core-collapse supernovae. The 21Na(αp)24Mg reaction could make a branch of the extended αp-process and could be important to understand the production of 22Na during the hydrogen explosion at high temperature, like in X-ray bursts, and the 44Ti production from core-collapse supernovae.

Proton resonant states in 26Si have been studied by the resonant elastic scattering of 25Al+p with a 25Al radioactive ion beam at 2.863 MeV/nucleon bombarding a thick H2 gas target with the inverse kinematics method at the low-energy RI beam facility CRIB (CNS Radioactive Ion Beam separator), University of Tokyo. The properties of these resonance states are important to better determine the production rates of 25Al(p,γ)26Si reaction, which is one of the astrophysically important nuclear reactions to understand the production of the ground state of 26Al, the emitter of its characteristic 1.809-MeV gamma-ray, under the explosive stellar environments such as novae and X-ray bursts. In this work, several resonances above the proton threshold level have been observed with a high statistics and background free through a covered the range of excitation energies from Ex ∼ 6.8 to 8.2 MeV.

Astrophysical 18Ne(α,p)21Na reaction is one of the most probable breakout routes, which lead to the rp-process from the hot-CNO cycle, converting the initial CNO elements into heavier elements in Type I x-ray bursters. Presently, there is no much experimental cross-section data reported at the energy of astrophysical interest, and resonant spectroscopic information in compound 22Mg is scarce as well. The experiment has been carried out by using the CNS radioactive ion beam separator (CRIB). Resonant properties in 22Mg have been studied via the resonant elastic scattering of 21Na+p, and cross section of the time-reversal reaction of 21Na(p,α)18Ne been measured simultaneously. A wide excitation energy region up to Ex ∼ 9.5 MeV in 22Mg has been scanned with a thick-target method. Some preliminary results will be reported.

The structure of proton-unbound states in {sup 30}{sub S} and {sup 31}{sub S} is important for determining the {sup 29}P(p,{gamma}){sup 30}S and {sup 30}P(p,{gamma}){sup 31}S reaction rates, which influence explosive hydrogen burning in classical novae. The former reaction rate in this temperature regime had been previously predicted to be dominated by two low-lying, unobserved, J{sup {pi}} = 3{sup +} and 2{sup +} resonances in {sup 30}S. To search for evidence for these levels, the structure of {sup 30}{sub S} was studied using the {sup 32}S(p,t){sup 30}S reaction with a magnetic spectrograph. We provide an update on the status of the ongoing analysis and some preliminary results.

Over the past three years, we have worked on developing a well-characterized 30S radioactive beam to be used in a future experiment aiming to directly measure the 30S(alpha,p) stellar reaction rate within the Gamow window of Type I X-ray bursts. The importance of the 30S(alpha,p) reaction to X-ray bursts is discussed. Given the astrophysical motivation, the successful results of and challenges involved in the production of a low-energy 30S beam are detailed. Finally, an overview of our future plans regarding this on-going project are presented., 7 pages, 2 figures, 5th European Summer School on Experimental Nuclear Astrophysics, Santa Tecla, Sicily, September 2009

Over the past three years, we have worked on developing a well-characterized 30S radioactive beam to be used in a future experiment aiming to directly measure the 30S(alpha,p) stellar reaction rate within the Gamow window of Type I X-ray bursts.

The measurement of the resonant alpha scattering and the 21Na(α, p) reaction were performed for the first time in inverse kinematics with the thick target method using a 21Na radioisotope (RI) beam. This paper reports the current result of alpha scattering measurement and its astrophysics implication.

CRIB (CNS Radioactive Ion Beam separator) is a low‐energy RI beam separator at the Center for Nuclear Study (CNS) of the University of Tokyo. Using the RI beams at CRIB, Many measurements on proton and alpha resonance scatterings, (α,p) reactions, and others were peformed in recent years, mainly for studying astrophysical reactions and exotic nuclear structure. Among them, the results on the 7Be+p and 7Li+α resonance scatterings are presented.

A small fraction of presolar SiC grains is suggested to have been formed in the ejecta of classical novae. The Si isotopic abundances in such grains can be determined from the 29P(p,γ)30S reaction rate at nova temperatures. The Si isotopic abundances provide us with information on the nature of the probable white dwarf progenitor’s core, as well as the peak temperatures achieved during nova outbursts, and thus the nova nucleosynthetic path. The 29P(p,γ)30S reaction rate at nova temperatures is determined by two low‐lying 3+ and 2+ resonances above the proton threshold at 4399 keV in 30S. However, only one of these two states has only been observed very recently. We have studied the 30S nuclear structure via the 32S(p,t)30S reaction at 5 laboratory angles between 9° to 62°. We have observed 14 states, eleven of which are above the proton threshold, including two levels at 4692.7±4.5 keV and 4813.8±3.4 keV that are candidates for the 3+ and the previously “missing” 2+ state, respectively.

CRIB (CNS Radioactive Ion Beam separator ) is a low‐energy RI beam separator at the Center for Nuclear Study (CNS) of the University of Tokyo. Using the RI beams at CRIB, many measurements on proton alpha resonance scatterings, (α,p) reactions, and others were performed in recent years mainly for studying astrophysical reactions and exotic nuclear structure. Among them, the results on the 7Li+α resonance scatterings are presented.

CRIB (CNS Radioactive Ion Beam separator) is a low‐energy RI beam separator at the Center for Nuclear Study (CNS) of the University of Tokyo, used for various studies covering nuclear‐astrophysical topics. An application of the RI beam at CRIB for the astrophysical studies is a new measurement of the proton resonance scattering on 7Be. The measurement was performed up to the excitation energy of 6.8 MeV, ans the excitation function above 3.5 MeV was successfully measured for the first time, providing important information about the reaction rate of 7Be(p,γ)8B, which is the key reaction in the solar 8B neutrino production. A preliminary result of the 7Be+p experiment is presented.

The 12C(α,γ)16O reaction is of great importance for the understanding the nuclear synthesis and explosion mechanism of the supernova. The cross section at the relevant stellar burning energies, around 300 keV, is dominated by the sub‐threshold resonances. The 16N β‐delayed α decay data provide the most sensitive constrain on this sub‐threshold resonance. Using twin‐ionization chambers, we have measured the α particles and 12C recoil nuclei in coincidence. The spectrum has been fitted together with the published 12C(α,γ)16O data and the elastic scattering phase shift data using R‐matrix. The SE1 factor at 300 keV has been determined as 73±21 keVb.