The α resonant scattering on ¹⁸Ne was measured in inverse kinematics to understand the α-clustering of proton-rich ²²Mg nucleus, performed at the CNS Radio-Isotope Beam Separator (CRIB) of Center for Nuclear Study, University of Tokyo, located at the RIBF of RIKEN Nishina Center. The excitation function of ²²Mg was obtained for the excitation energies of 10--16 MeV by adopting the thick-target method. Several resonances were evident in the present work, which implies the existence of energy levels with large α widths. Since energy levels were not clearly observed at the astrophysically important energy range, upper limits on the ¹⁸Ne (α, α)¹⁸Ne cross section were set. The astrophysical impact was also investigated by estimating the ¹⁸Ne (α, p)²¹Na cross section.

The dynamics of a nuclear open quantum system could be revealed in the correlations between the breakup fragments of halo nuclei. The breakup mechanism of a proton halo nuclear system is of particular interest as the Coulomb polarization may play an important role, which, however, remains an open question. Here we use a highly efficient silicon detector array and measure the correlations between the breakup fragments of 8B incident on 120Sn at near-barrier energies. The energy and angular correlations can be explained by a fully quantum mechanical method based on the state-of-the-art continuum discretized coupled channel calculations. The results indicate that, compared to the neutron halo nucleus 6He, 8B presents distinctive reaction dynamics: the dominance of the elastic breakup. This breakup occurs mainly via the short-lived continuum states, almost exhausts the 7Be yield, indicating the effect of Coulomb polarization on the proton halo state. The correlation information reveals that the prompt breakup mechanism dominates, occurring predominantly on the outgoing trajectory. We also show that, as a large environment, the continuum of 8B breakup may not significantly influence elastic scattering and complete fusion.

The cosmological lithium problem (CLP) stems from the outstanding discrepancy between theoretical predictions and astronomical observations of primordial lithium abundances. For the radiogenic production of 7Li, 7Be plays a pivotal role in the Big Bang nucleosynthesis (BBN). Nevertheless, the data for neutron-induced 7Be destruction processes were still sparse, and especially lacked information on the contributions of transitions to the 7Li excited states. In this work, we have determined the 7BeLi, 7BeLi*, and 7BeHe reaction cross sections by means of the Trojan Horse method. The present and the previous data were analyzed together by a multichannel R-matrix fit, providing an improved uncertainty evaluation of the channel and the first-ever quantification of the contribution in the BBN-relevant energy range. We implemented the revised total reaction rate summing both the and contributions in a state-of-the-art BBN code PRIMAT. As a consequence, the present nuclear-physics data offers a reduction of the predicted 7Li abundance by about one-tenth, which would impose a stricter constraint on BBN and head us in the correct direction to the CLP solution.

The mechanism of reactions with weakly-bound proton-rich nuclei at energies near the Coulomb barrier is a long-standing open question owing to the paucity of experimental data. In this study, a complete kinematics measurement was performed for the proton drip-line nucleus 17F interacting with 58Ni at four energies near the Coulomb barrier. Thanks to the powerful performance of the detector array, exhaustive information on the reaction channels, such as the differential cross sections for quasielastic scattering, exclusive and inclusive breakup, as well as for fusion-evaporation protons and alphas, was derived for the first time. The angular distributions of quasielastic scattering and exclusive breakup can be described reasonably well by the continuum-discretized coupled-channels calculations. The inclusive breakup was investigated using the three-body model proposed by Ichimura, Austern, and Vincent, and results indicate the non-elastic breakup is the dominant component. The total fusion cross sections were determined by the fusion-evaporation protons and alphas. Based on the measured exclusive breakup data, the analysis of the classical dynamical simulation code PLATYPUS demonstrates that the incomplete fusion plays a minor role. Moreover, compared with 16O+58Ni, both the reaction and total fusion cross sections of 17F+58Ni exhibit an enhancement in the sub-barrier energy region, which mainly arises from couplings to the continuum states. This work indicates that the information of full reaction channels is crucially important to comprehensively understand the reaction mechanisms of weakly bound nuclear systems.

We report on the development of a new, portable detector array for charged particles with a low detection threshold to study the reaction mechanisms of exotic nuclear systems at energies around the Coulomb barrier. In order to identify both light and heavy particles simultaneously, the array consists of ten units of ΔE-E telescopes, where each one is made up of four detection layers: one ionization chamber, one 40 (or 60)μm double-sided silicon strip detector and two quadrant silicon detectors with thicknesses of 300μm and 1000 (or 1500)μm, respectively. The frame of the ionization chamber is innovatively designed with printed circuit boards, thus the mass of each telescopic unit was reduced significantly which eases transport and installation requirements to different radioactive ion beam lines around the globe. The commissioning experiments focused on elucidating several reaction mechanisms encountered in the 17F + 58Ni and 17F + 208Pb systems, and we demonstrated that the array has a sufficient capability to enable charged particle identification over a large range of Z. Light particles like p, d, α as well as heavy ions like 16O and 17F can be clearly distinguished. Considering these properties, this newly developed array enables in-depth investigation of the novel reaction mechanisms which are manifested in the collisions of exotic nuclei with differing isotopes.

We conducted a measurement of 18Ne + α scattering in inverse kinematics, in order to search for experimental evidence of α-cluster structure in ²²Mg above the alpha threshold (Ethr = 8.14MeV) and determine the astrophysical rates of the ¹⁸Ne(α, p)²¹Na reaction under the conditions of break-out from the Hot-CNO cycle. A high intensity ¹⁸Ne beam at 2.54 AMeV was successfully produced at CRIB (CNS Radioactive Ion Beam separator) of the Center for Nuclear Study, the University of Tokyo. This paper presents the in-flight production of the radioactive 18Ne beam by using the production reaction ³He(¹⁶O, ¹⁸Ne)n with a windowed cryogenic gas target, which was employed in the mentioned resonant α-scattering experiment.

The intense γ-rays from classical novae are emitted due to the β-decay of 18F which is produced by the Hot-CNO cycle. The reaction rate of 18F(p,α)15O affects the prediction of the abundance of 18F. The main contribution to this reaction rate is from the resonances in 19Ne near and above the proton threshold. Hence, many experiments and theoretical works have been performed on the low-lying 18F+p resonances. One of the methods for investigating 19Ne parameters is studying the mirror nucleus 19F. α elastic scattering experiment was performed with a 7 MeV/u 15N beam for investigating the resonance parameters in 19F using the thick target method in inverse kinematics at the radioactive beam facility CRIB of the Center for Nuclear Study, the University of Tokyo. The excitation function of 19F was obtained for the excitation energy Ex = 6.7 - 7.7 MeV, and the parameters of the resonance states in 19F were determined using an R-matrix analysis.

The α-clusterization of an atomic nucleus has been studied for a long time, even from the earliest days of nuclear physics. Our understanding of the α-cluster structure is, however, mainly limited to the self-conjugate A = 4n (n = 2, 3, 4, ... ) light nuclei and some of the neutron-rich radionuclides such as 10Be, 11B, and 14C. In order to study the α-cluster structure of a neutron-deficient 22Mg nucleus, we have measured the 18Ne(α, α)18Ne scattering in inverse kinematics by using radioactive 18Ne beams and the 4He gas target at the Center for Nuclear Study radioactive ion beam separator of the University of Tokyo. Recoiling α particles from the scattering were detected by using silicon strip detectors, which constitute ΔE-E telescopes for particle identification. By adopting a thick target method, we were able to investigate a wide range of excitation energies Ex = 9.9 - 16.5 MeV in 22Mg in this work.

Abstract It is a well-known fact that a cluster of nucleons can be formed in the interior of an atomic nucleus, and such clusters may occupy molecular-like orbitals, showing characteristics similar to normal molecules consisting of atoms. Chemical molecules having a linear alignment are commonly seen in nature, such as carbon dioxide. A similar linear alignment of the nuclear clusters, referred to as linear-chain cluster state (LCCS), has been studied since the 1950s, however, up to now there is no clear experimental evidence demonstrating the existence of such a state. Recently, it was proposed that an excess of neutrons may offer just such a stabilizing mechanism, revitalizing interest in the nuclear LCCS, specifically with predictions for their emergence in neutron-rich carbon isotopes. Here we present the experimental observation of α-cluster states in the radioactive ¹4C nucleus. Using the ¹⁰Be + α resonant scattering method with a radioactive beam, we observed a series of levels which completely agree with theoretically predicted level having an explicit linear-chain cluster configuration. We regard this as the first strong indication of the linear-chain clustered nucleus.

Software for genuinely event-by-event analysis and event reconstruction of data obtained by using an active target has been developed in the graphical user interface under the CERN ROOT framework. The primary motivation for developing the software was to provide physicists who perform experiments using an active target a more user-friendly environment for the purpose of investigating the performance of detection systems and obtaining ideas about physics from a large amount of experimental data. To test the performance of the software, we analyzed experimental data from a 16N radioactive ion beam experiment for α-decay measurements. As a result of the analysis, we observed the Bragg curve and measured the range of the 16N RI beam in the detector. Data were calibrated against the calculation after comparing the Bragg curve to the one obtained from an energy loss calculation in P-10 gas. We present a detailed description of the analysis software and its test results.

The ¹⁸Ne(α,p)²¹Na reaction is thought to be one of the key breakout reactions from the hot CNO cycles to the rp process in type I x-ray bursts. In this work, the resonant properties of the compound nucleus ²²Mg have been investigated by measuring the resonant elastic scattering of ²¹Na + p. An 89-MeV ²¹Na radioactive beam delivered from the CNS Radioactive Ion Beam Separator bombarded an 8.8 mg/cm² thick polyethylene (CH₂)n target. The ²¹Na beam intensity was about 2×10⁵ pps, with a purity of about 70% on target. The recoiled protons were measured at the center-of-mass scattering angles of θ_c.m.˜175.2^o, 152.2^o, and 150.5^o by three sets of ΔE-E telescopes, respectively. The excitation function was obtained with the thick-target method over energies E_x(²²Mg)=5.5-9.2 MeV. In total, 23 states above the proton-threshold in ²²Mg were observed, and their resonant parameters were determined via an R-matrix analysis of the excitation functions. We have made several new J^π assignments and confirmed some tentative assignments made in previous work. The thermonuclear ¹⁸Ne(α,p)²¹Na rate has been recalculated based on our recommended spin-parity assignments. The astrophysical impact of our new rate has been investigated through one-zone postprocessing x-ray burst calculations. We find that the ¹⁸Ne(α,p)²¹Na rate significantly affects the peak nuclear energy generation rate, reaction fluxes, and onset temperature of this breakout reaction in these astrophysical phenomena.

The evolution of massive stars with very low-metallicities depends critically on the amount of CNO nuclides which they produce. The ¹²N(p,γ)¹³O reaction is an important branching point in the rap processes, which are believed to be alternative paths to the slow 3α process for producing CNO seed nuclei and thus could change the fate of massive stars. In the present work, the angular distribution of the ²H(¹²N, ¹³O)n proton transfer reaction at E_c.m.=8.4 MeV has been measured for the first time. Based on the Johnson-Soper approach, the square of the asymptotic normalization coefficient (ANC) for the virtual decay of ¹³O_g.s. → ¹²N+p was extracted to be 3.92 ± 1.47 fm^-1 from the measured angular distribution and utilized to compute the direct component in the ¹²N(p,γ)¹³O reaction. The direct astrophysical S factor at zero energy was then found to be 0.39 ± 0.15 keV b. By considering the direct capture into the ground state of ¹³O, the resonant capture via the first excited state of ¹³O and their interference, we determined the total astrophysical S factors and rates of the ¹²N(p,γ)¹³O reaction. The new rate is two orders of magnitude slower than that from the REACLIB compilation. Our reaction network calculations with the present rate imply that ¹²N(p,γ)¹³O will only compete successfully with the β⁺ decay of ¹²N at higher (∼2 orders of magnitude) densities than initially predicted.

The ¹⁸Ne(α,p)²¹Na reaction provides a pathway for breakout from the hot CNO cycles to the rp process in type-I x-ray bursts. To better determine this astrophysical reaction rate, the resonance parameters of the compound nucleus ²²Mg have been investigated by measuring the resonant elastic scattering of ²¹Na+p. An 89 MeV ²¹Na radioactive ion beam was produced at the CNS Radioactive Ion Beam Separator and bombarded an 8.8 mg/cm² thick polyethylene target. The recoiled protons were measured at scattering angles of θ_c.m.˜175^o and 152^o by three ΔE-E silicon telescopes. The excitation function was obtained with a thick-target method over energies E_x(²²Mg) = 5.5--9.2 MeV. The resonance parameters have been determined through an R-matrix analysis. For the first time, the J^pi values for ten states above the α threshold in ²²Mg have been experimentally determined in a single consistent measurement. We have made three new J^pi assignments and confirmed seven of the ten tentative assignments in the previous work. The ¹⁸Ne(α,p)²¹Na reaction rate has been recalculated, and the astrophysical impact of our new rate has been investigated through one-zone postprocessing x-ray burst calculations. We find that the ¹⁸Ne(α,p)²¹Na rate significantly affects the peak nuclear energy generation rate and the onset temperature of this breakout reaction in these phenomena.

Background: In presolar low-density graphite grains, an extraordinarily large ²²Ne/²⁰Ne ratio or even nearly pure ²²Ne is found, pointing to the condensation of radioactive ²²Na in grains. Supernovae and neon-rich novae are the main events that produce ²²Na via the explosive hydrogen burning process. The ²²Na(p, γ)²³Mg reaction is one of the key reactions that influences the ²²Na abundance in ejecta.Purpose:The present work aims to explore the proton resonant states in ²³Mg relevant to the astrophysical ²²Na(p, γ)²³Mg reaction. The determined ²³Mg resonant parameters can be used to evaluate the ²²Na(p, γ)²³Mg reaction rate.Method:A low-energy ²²Na radioactive ion beam is produced via the ¹H(²²Ne, ²²Na)n reaction, and used to measure the experimental excitation function of the ²²Na + p resonant scattering with a conventional thick-target inverse kinematic method. R-matrix analysis is applied to deduce the ²³Mg resonance parameters from the experimental excitation function.Results: Three proton resonance states in ²³Mg are observed. Spins/parities and the proton partial widths are determined. The deduced excitation energies agree with the compiled values.Conclusions: The new spin and parity assignments allow us to perform a shell-model calculation of the γ widths of the ²³Mg resonant states for the evaluation of the ²²Na(p, γ)²³Mg astrophysical reaction rate. The two s-wave resonant states established in this work at 8.793 and 8.916 MeV in ²³Mg, respectively, increase the total reaction rate by about 5% at a temperature greater than 2 GK.

Background: The resonance structure in ¹¹C is of particular interest with regard to the astrophysical ⁷Be(α,γ) reaction, relevant at high temperature, and to the α-cluster structure in ¹¹C.
Purpose: The measurement was made to determine the unknown resonance parameters for the high excited states of ¹¹C. In particular, the α-decay width can be useful information to discuss the α-cluster structure in ¹¹C.
Methods: New measurements of ⁷Be+α resonant scattering and the ⁷Be(α,p)¹⁰B reaction in inverse kinematics were performed for center-of-mass energy up to 5.5 MeV, and the resonances at excitation energies of 8.9--12.7 MeV in the compound ¹¹C nucleus were studied. Inelastic scattering of ⁷Be+α and the ⁷Be(α,p₁)¹⁰B^* reaction were also studied with a simultaneous γ-ray measurement. The measurements were performed at the low-energy radioactive ion beam facility CRIB (CNS Radioactive Ion Beam separator) of the Center for Nuclear Study, the University of Tokyo.
Results: We obtained excitation functions of ⁷Be(α,α₀)⁷Be (elastic scattering), ⁷Be(α,α₁)⁷Be^* (inelastic scattering), ⁷Be(α,p₀)¹⁰B, and ⁷Be(α,p₁)¹⁰B^*. Many resonances including a new one were observed and their parameters were determined by using an R-matrix analysis.
Conclusions: The resonances we observed possibly enhance the ⁷Be(α,γ) reaction rate but with a smaller magnitude than the lower-lying resonances. A new negative-parity cluster band, similar to the one previously suggested in the mirror nucleus ¹¹B, is proposed.

²⁵Al+p elastic scattering in inverse kinematics was measured to explore the level structure of ²⁶Si above its proton threshold. The ²H(²⁴Mg,n)²⁵Al reaction was used to produce a 3.4 MeV/nucleon ²⁵Al radioactive beam with intensities of about 10⁶ ions per second on target. By using a thick target of (CH₂)_n, a center-of-mass energy range of 3 MeV was scanned, reaching up to about 8.5 MeV in excitation energy in ²⁶Si. This energy range covered the region of importance for the ²⁵Al(p,γ)²⁶Si at temperatures characteristic of explosive nucleosynthesis. Level parameters of six strong s-wave ²⁵Al+p resonances in ²⁶Si were extracted from fits to the measured excitation functions using the R-matrix formalism. Two new levels have been discovered, while for two others, our spin-parity assignments disagree with the results of some previous studies. Lastly, our resonance parameters for the remaining two levels are in good agreement with past experimental work, and with recent shell-model calculations.

Proton resonant states in ²⁷P were studied by the resonant elastic scattering of ²⁶Si+p with a ²⁶Si radioactive ion beam bombarding a thick H₂ gas target with the inverse kinematics method. The properties of these resonance states are important to better constrain the production rates of the ²⁶Si(p,γ)²⁷P reaction. This is one of the astrophysically important reactions needed to understand proton-rich nucleosynthesis such as the galactic production of ²⁶Al and energy generation in explosive stellar environments. Although there are recent studies on the resonant structure in ²⁷P, large uncertainties remain, and only a few levels are known. In this work, resonant states were observed over the excitation energies range of 2.3 to 3.8 MeV with high statistics and without background contamination within the target. The resonance parameters were extracted by an R-matrix analysis of the excitation function. The ²⁶Si(p,γ)²⁷P stellar reaction rate has been evaluated, including high-lying resonances found in this work.

The quasi-elastic scattering angular distribution of the proton drip line nucleus ¹⁷F on a ¹²C target was measured at 60 MeV. The experimental data have been compared with the theoretical analysis based onto optical model and continuum discretized coupled channels (CDCC). The couplings between breakup and elastic scattering channels, and between inelastic and elastic scattering channels resulted very weak. In order to explore the breakup effects the total reaction cross-section was deduced from the angular distribution of the quasi-elastic scattering data, and then compared with the existing data for the other weakly and tightly bound nuclei on ¹²C target using a universal function. From this comparison, we concluded that the breakup effect is not important for weakly bound projectiles on the light target as obtained also with the CDCC analysis.

A new measurement of α resonant scattering on ⁷Li was performed over the excitation energy of 10.2-13.0 MeV in ¹¹B at the low-energy RI beam facility CNS Radioactive Ion Beam separator (CRIB) of the Center for Nuclear Study (CNS), University of Tokyo. The excitation function of ⁷Li+α at 180^o in the center-of-mass system was successfully measured for the first time with the inverse kinematics method, providing important information on the α cluster structure in ¹¹B and the reaction rate of ⁷Li(α,γ), which is relevant to the ¹¹B production in the ν process in core-collapse supernovae. The excitation function of the ⁷Li(α,p) reaction cross section for 11.7-13.1 MeV was also measured.

For the study of astrophysically important states in ¹⁸Ne, the ¹⁴O(α,α)¹⁴O cross section was measured ininverse kinematics using a radioactive ¹⁴O beam. This reactionwas investigated for properties of resonant states of ¹⁸Ne for determining the ¹⁴O(α,p)¹⁷F reaction rate, which isone of the most important reactions for understanding the breakoutmechanism from the Hot CNO cycle to the rp-process. Alpha inducedelastic scattering on ¹⁴O was performed using the low-energy RI beam separator at Center for Nuclear Study, in the RIKEN Accelerator Research Facility. The energy range E_x= 7.2 ~13.1 MeV of ¹⁸Ne was scanned with the thick target method. Recoiled alpha particles were measured with Si dE-E telescopes. Spins and widths of three resonances at E_x = 8.6, 9.22, and 10.06 MeV were calculated using the R-matrix analysis and a new state of ¹⁸Ne at E_x=12.0 MeV was found in this experiment.

The excited states in ²²Mg have been investigated by the resonant elastic scattering of ²¹Na+p. A 4.0 MeV/nucleon ²¹Na beam was separated by the Center for Nuclear Study (CNS) radioactive ion beam separator (CRIB) and then used to bombard a thick (CH₂)_n target. The energy spectra of recoiled protons were measured at scattering angles of θ_c.m.˜172^o,146^o, and 134^o, respectively. A wide energy-range of excitation function in ²²Mg (up to E_x˜8.9 MeV) was obtained simultaneously with a thick-target method, and a state at 7.06 MeV was newly observed. The resonant parameters were deduced from an R-matrix analysis of the center-of-mass (c.m.) differential cross-section data with a SAMMY-M6-BETA code. The astrophysical resonant reaction rate for the ¹⁸Ne(α,p)²¹Na reaction was recalculated based on the present parameters. Generally speaking, the present rates are much smaller than the previous ones.

A new measurement of proton resonance scattering on ⁷Be was performed up to the center-of-mass energy of 6.7 MeV using the low-energy RI beam facility CRIB (CNS Radioactive Ion Beam separator) at the Center for Nuclear Study of the University of Tokyo. The excitation function of ⁷Be+p elastic scattering above 3.5 MeV was measured successfully for the first time, providing important information about the resonance structure of the ⁸B nucleus. The resonances are related to the reaction rate of ⁷Be(p,γ)⁸B, which is the key reaction in solar ⁸B neutrino production. Evidence for the presence of two negative parity states is presented. One of them is a 2^- state observed as a broad s-wave resonance, the existence of which had been questionable. Its possible effects on the determination of the astrophysical S-factor of ⁷Be(p,γ)⁸B at solar energy are discussed. The other state had not been observed in previous measurements, and its spin and parity were determined as 1^-.

Proton resonances in ²²Mg have been investigated by the resonant elastic scattering of ²¹Na + p. The ²¹Na beam with a mean energy of 4.00 MeV/nucleon was separated by the CNS radioactive-ion-beam separator (CRIB) and bombarded a thick (CH₂)_n target. The energy spectra of recoiled protons were measured at scattering angles of θ_c.m. ˜ 172^o , 146^o , respectively. Several excited states observed before have been confirmed including two states (at 6.616, 6.796 MeV) observed at TRIUMF. A new state at 7.06 MeV has been observed, and another new one at 7.28 MeV is tentatively identified due to its low statistics. The proton resonant parameters were deduced from an R-matrix analysis of the differential cross-section data with a SAMMY-M6-BETA code. The astrophysical implication for the ¹⁸Ne(α, p)²¹Na reaction has been briefly discussed.

A cryogenic gas target system was developed for the radioisotope (RI) beam production at CNS Radio Isotope Beam separator (CRIB). Hydrogen gas was cooled to 85 90 K using liquid nitrogen and used as a secondary beam production target having a thickness of 2.3mg/cm². An intense ⁷Be beam (2×10⁸ particles per second) was successfully produced using this target. We observed a density-reduction effect at the gas target for high-current primary beams with about 7.5 W heat deposition. One main feature of the target system is forced circulation of the target gas. We have found that the circulation of the target gas at a rate of 55 standard liters per minute (slm) was effective in eliminating the density reduction. The extent to which the forced flow can prevent the density reduction had not been known well. In this work, the relation between the density reduction and the forced circulation rate was quantitatively studied.

Proton resonant states in ²³Al have been investigated for the first time by the resonant elastic and inelastic scattering of ²²Mg+p with a ²²Mg beam at 4.38 MeV/nucleon bombarding a thick (CH₂)_n target. The low-energy ²²Mg beam was separated by the CNS radioactive ion beam separator (CRIB). The energy spectra of recoiled protons were measured at average scattering angles of θ_lab˜4^o,17^o and 23^o. A new state has been observed at E_x=3.00 MeV with a spin-parity assignment of (3/2⁺). In addition, resonant inelastic scattering has populated three more states at excitation energies of 3.14, 3.26, and 3.95 MeV, with proton decay to the first excited state in Mg22 being observed. The new state at 3.95 MeV has been assigned a spin-parity of J^π=(7/2⁺). The resonant parameters were determined by an R-matrix analysis of the excitation functions with a SAMMY-M6-BETA code. The core-excited structure of ²³Al is discussed within a shell-model picture. The stellar reaction rate of the ²²Mg(p,γ)²³Al reaction has been reevaluated, and the revised total reaction rate is about 40% greater than the previous result for temperatures beyond T₉=0.3.

Single-particle properties of low-lying resonance levels in ¹⁴O have been studied efficiently by utilizing a technique of proton elastic resonance scattering with a ¹³N secondary beam and a thick proton target. The excitation functions for the N13+p elastic scattering were measured over a wide energy range of E_cm=0.4--3.3 MeV and fitted with an R-matrix calculation. A clear assignment of J^π=2^- has been made for the level at E_x=6.767(11) MeV in ¹⁴O for the first time. The excitation functions show a signature of a new 0^- level at E_x=5.71(2) MeV with Γ=400(100) keV. The excitation energies and widths of the ¹⁴O levels are discussed in conjunction with the spectroscopic structure of A=14 nuclei with T=1.

A low-energy in-flight type RI beam separator, called CRIB, has been installed for nuclear physics and nuclear astrophysics by the Center for Nuclear Study, the University of Tokyo in the RIKEN Accelerator Research Facility. It consists of a double achromatic system and an Wien filter. It is capable of providing RI beams at 5?10 MeV/nucleon. Since CRIB has been developed in the end of 2000, many proton-rich RI beams were successfully produced via the (p,n), (d,t), and (3He,n) reactions in inverse kinematics. In this paper, the design of the separator and its performance are discussed including the method of RI-beam production at low energies.

Resonance states in ¹²N were studied by using the resonance elastic scattering of ¹¹C+p with a low-energy radioactive ion beam of ¹¹C at 3.5 MeV/nucleon and a thick (CH₂)_n target. The ¹¹C beam was separated by a newly installed CNS radioactive ion beam separator (CRIB). The energy spectrum of recoil protons was measured at laboratory scattering angles around θ_LAB=0^o to identify resonance states in ¹²N. The spin-parity values of J^π=3^- and (2)⁺ have been determined for the levels at the excitation energies of E_x=3.1 and 3.6 MeV in ¹²N, respectively, suggesting a small contribution of the 3.1-MeV level to the ¹¹C(p,γ)¹²N stellar reaction.

An in-flight RIB separator at low energies, which is the first extensive separator at low energies, called CRIB, is just under construction at CNS. This consists of a double-achromatic magnetic separator, a window-less gas target, and a Wien filter. Some characteristics of the CRIB are described. Possible experimental plans are also discussed in our nuclear astrophysics project for the study of the explosive hydrogen burning process, especially on the onset mechanism.

Our research goal is to measure the cross section of the 7Be(d, p) reaction to find a solution for the cosmological the 7Li problem, which is an overestimation of the primordial 7Li abundance in the standard Big-Bang nucleosynthesis (BBN) model. We developed a method to produce an unstable 7Be target to measure the reaction in normal kinematics in a high-resolution measurement. We performed an experiment to produce the 7Be target and also to measure the cross section of the 7Be(d, p)8Be reaction with the produced 7Be target at the tandem facility, Kobe University. A 2.36 MeV proton beam irradiated a Li target to transmute 7Li particles to 7Be particles via the 7Li(p, n)7Be reaction. We produced 2.6×10¹³ 7Be particles in the target after two days’ proton irradiation. After the target production, the beam ion was changed to deuterons with energies of 0.6, 1.0, and 1.6 MeV to measure the 7Be(d, p) reaction. The outgoing protons were measured by two ΔE-E silicon telescopes placed at 30^o and 45^o. We report the preliminary results of this experiment, including the 7Be(d, p) cross section.

Studies on nuclear astrophysics, nuclear structure, and other interests have been performed using the radioactive-isotope (RI) beams at the low-energy RI beam separator CRIB, operated by Center for Nuclear Study (CNS), the University of Tokyo. The elastic resonant scattering is a striking tool to study astrophysical reactions and nuclear clusters. In particular, when it is coupled with a thick target and inverse kinematics, the measurement can be very efficient and even feasible with RI beams. By measuring resonant scattering, we can study the properties of resonant states which could play an important role in the astrophysical reaction, or have an exotic nuclear structure. The 10Be+α elastic scattering has been measured at CRIB, and three resonances which are in agreement with the prediction of a linear-chain structure by Suhara-En’yo were observed, giving a strong indication of the existence of such an exotic structure. Measurements based on the indirect technique of the reaction measurement, such as the Trojan horse method, have also been performed at CRIB.

The elastic scattering process for the nuclear reactions induced by the Radioactive Ion Beams 7Be and 8B on a 208Pb target was measured for the first time in the energy range around the Coulomb barrier. Extensive theoretical calculations within the framework of the optical model were performed. An excellent agreement between experimental data and theoretical predictions was achieved for the reaction 7Be + 208Pb, while a comprehensive understanding of the reaction dynamics induced by the more exotic projectile 8B is still far to be reached. Predictions of the cross section for the breakup for both systems will also be given.

Studies on nuclear astrophysics and nuclear structure have been performed using the radioactive-isotope (RI) beams at the low-energy RI beam separator CRIB of the University of Tokyo. Recent studies on astrophysical reactions in high-temperature stellar environments at CRIB are discussed. We conducted a series of $$alpha $$resonant scattering measurements with RI beams and the thick-target method, mainly to evaluate astrophysical reaction rates of $$alpha $$-induced reactions. Experimental projects based on other experimental techniques, such as the Trojan horse method or RI-implanted target, are also ongoing.

We performed indirect measurements of the neutron-induced reactions $$^{7}$$Be(n,p)$$^{7}$$Li and $$^{7}$$Be(n,$$mathsf alpha $$)$$^{4}$$He simultaneously by the Trojan Horse method relevant to the cosmological $$^7$$Li problem. Preliminary excitation functions for $$(n,p_0)$$and $$(n,alpha )$$are basically consistent with the previous studies, and new information about the $$(n,p_1)$$contribution suggests possible enhancement of the total reaction rate.

The cosmologically relevant ⁷Be(n,α)⁴He has been matter of recent studies aimed at contributing to the long-standing Li-problem. Here a brief description of the twin THM investigations will be shown and the main results discussed.

The scattering process of weakly-bound nuclei at Coulomb barrier energies provides deep insights on the reaction dynamics induced by exotic nuclei. Within this framework, we measured for the first time the scattering process of the short-lived Radioactive Ion Beam (RIB) 8B (Sp = 0.1375 MeV) from a 208Pb target at 50 MeV beam energy. The 8B RIB was produced by means of the in-flight facility CRIB (RIKEN, Japan) with an average intensity on target of 10 kHz and a purity about 25Elastically scattering ions were detected in the angular range θc.m. = 10°-160^o by means of the detector array EXPADES. A preliminary optical model analysis indicates a total reaction cross section of about 1 b, a value, once reduced, 2-3 times larger than those obtained for the reactions induced by the stable weakly-bound projectiles 6,7Li on a 208Pb target in the energy range around the Coulomb barrier.

Astrophysical observables that are directly linked to nuclear physics inputs provide critical and stringent constraints on nucleosynthetic models. As 26Al was the first specific radioactivity observed in the Galaxy, its origin has fascinated the nuclear astrophysics community for nearly forty years. Despite extensive research, the precise origins of 26Al remain elusive. At present, the sum of all putative stellar contributions generally overestimates the 26Al mass in the interstellar medium. Among the many reactions that influence the yield of 26Al, radiative proton capture on its isomer 26mAl is one of the least constrained reactions by experimental data. To this end, we developed a 26Al isomeric beam and performed proton elastic scattering to search for low-spin states in 27Si. The experimental method and the preliminary results of this on-going study will be presented.

The cosmological 7Li problem has been one of the big issues left in the standard Big-Bang nucleosynthesis (BBN) model. In order to determine the radiogenic 7Li abundance by the BBN, it is important to know the production and the destruction rate of 7Be rather than 7Li itself. We performed indirect measurements of the relevant neutron-induced reactions 7Be(n, p)7Li and 7Be(n, α)4He simultaneously by the Trojan Horse Method (THM) via the three-body reactions 7Be(d,7Lip)1H and 7Be(d, αα)1H. A 7Be radioactive-isotope (RI) beam at 3.16 MeV/u was produced at Center-for-Nuclear-Study RI Beam (CRIB) separator. The Q-value spectra shows the evidence of the three-body channels of interest. We confirmedthat the THM was applicable to the present measurements by the momentum distributions of the spectator proton. Preliminary excitation functions are roughly consistent with the previous studies, moreover providing new data in the BBN energy range, and suggesting that new information about the 7Be(n, p1)7Li* contribution may be obtained by carrying out a further data analysis.

Studies on nuclear astrophysics, nuclear structure, and other interests have been performed using the radioactive-isotope (RI) beams at the low-energy RI beam separator CRIB, operated by Center for Nuclear Study (CNS), the University of Tokyo. A type of measurement to study astophysical reactions at CRIB is by the elastα,γ resonant scattering with the thick-target method in inverse kinematics. An example is the α resonant scattering with 7Be beam, related to the astrophysical 7Be(α,γ) reactions, which is relevant in the hot p-p chain and νp-process in supernovae. Other α resonant scattering measurements with 30S, 10Be, 15O, and 18Ne beams have been performed at CRIB, using the thick-target method. There have also been measurements based on other experimental methods. The first Trojan horse method (THM) measurement using an RI beam has been performed at CRIB, to study the 18F(p, α)15O reaction at astrophysical energies via the three body reaction 2H(18F, α15O)n. The 18F(p, α)15O reaction rate is crucial to understand the 511-keV -ray production in nova explosion phenomena, and we successfully evaluated the reactio cross section at novae temperature and below experimentally for the first time.

In this contribution we describe the first results obtained for the investigation of the elastic scattering process in the reactions induced by the Radioactive Ion Beams 7Be and 8B on a 208Pb target at Coulomb barrier energies. The experimental data were analyzed within the framework of the optical model in order to extract the total reaction cross section. The comparison with data available in literature for reactions induced on 208Pb by light ions in the mass range A = 6-8 shows that the loosely-bound 8B has the largest reactivity.

Alpha resonant scattering is a simple and promising method to study α-cluster structure in nuclei. It has several good features which enable us to perform measurements with short-lived and relatively low-intense RI beams. Several measurements on alpha resonant scattering have been carried out at CRIB (CNS Radioactive Ion Beam separator), which is a low-energy RI beam separator at Center for Nuclear Study (CNS) of the University of Tokyo. Recent α resonant scattering studies at CRIB, using 7Li, 7Be and 10Be beams with a helium gas target, are discussed.

Studies on nuclear astrophysics, resonant structure, and nuclear reaction are going on at CRIB (CNS Radioactive Ion Beam separator), a low-energy RI beam separator operated by Center for Nuclear Study (CNS), the University of Tokyo. Two major methods used at CRIB to study nuclear reactions of astrophysical relevance are the resonant scattering, and direct measurements of (α,p) reactions using a thick-gas target. Several experiments for decay measurements and reaction mechanism are also performed using low-energy RI beams at CRIB. Some of the results from recent experiments at CRIB are discussed.

The ¹²C (α,γ)¹⁶O reaction at energies corresponding to the quiescent helium burning in massive stars is regarded as one of the most important processes in nuclear astrophysics. Although this process has being studied for over four decades, our knowledge of its cross section at the energies of interest for astrophysics is still widely unsatisfactory. Indeed, no experimental data are available around 300 keV and in the energy region of astrophysical interest extrapolations are performed using some theoretical approaches, usually R-matrix calculations. Consequently, the published astrophysical factors range from 1 to 288 keVb for S_E1(300) and 7 to 120 keVb for S_E2(300), especially because of the unknown contribution coming from subthreshold resonances. To improve the reliability of these extrapolations, data from complementary experiments, such as elastic and quasi-elastic α scattering on ¹²C , α-transfer reactions to ¹⁶O , and ¹⁶N decay are usually included in the analysis. Here the β-delayed α decay of ¹⁶N is used to infer information on the ¹²C (α,γ)¹⁶O reaction and a new experimental technique is suggested.

Alpha resonant scattering is a simple and promising method to study alpha-cluster structure in nuclei. It has several good features which enable us to perform measurements with short-lived and relatively low-intense RI beams. Several measurements on alpha resonant scattering have been carried out at CRIB (CNS Radioactive Ion Beam separator), which is a low-energy RI beam separator at Center for Nuclear Study (CNS) of the University of Tokyo. Recent alpha resonant scattering studies at CRIB, using 7Li, 7Be and 10Be beams with a helium gas target, are discussed.

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.

The excitation fuction of the ¹⁸Ne(α,p)²¹Na reaction in was directry measured using a new active target detector system. We are analyzing accumulated data. We will report the result of the development of the GEM - MSTPC and the preliminary results of the ¹⁸Ne(α,p)²¹Na a experiment.

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 determined the total reaction rate of the ¹¹C(α,p)¹⁴N 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 ¹¹C RI beams. We performed the identification of the ground-state transition and excited-state transitions using time-of-flight information for the first time.

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.

A measurement of resonant elastic scattering of ²⁶Si+p was performed with a thick target using a ²⁶Si radioactive ion beam at the CRIB (CNS Radioactive Ion Beam separator) of the Center for Nuclear Study (CNS), the University of Tokyo. The excitation function of ²⁷P was measured successfully with the inverse kinematics method through a covered the range of excitation energies from Ex ˜ 2.3 to 3.8 MeV, providing information about the resonance structure of this nucleus. The properties of these resonances are important to better determine the production rates of ²⁶Si(p,g)²⁷P reaction, which is one of the astrophysically important nuclear reactions to understand the production of the ²⁶Al. Some new resonant states have been investigated, and determined their resonance parameters, such as excitation energies, proton partial widths, and spin-parities by R-matrix calculation.

The rapid proton capture process (rp process) is a dominant reaction sequence in explosive hydrogen burning that synthesizes heavier elements, especially proton-rich unstable nuclides. Therefore, accurate thermonuclear reaction rates for (p,γ) reactions on the rp process path are essential for an understanding of the nucleosynthesis processes and energy production. We studied proton resonant states in ²⁶Si and ²⁷P via elastic scattering in inverse kinematics at the low-energy RI beam facility CRIB (CNS Radioactive Ion Beam separator), University of Tokyo. By using a thick H₂ gas target, excitation energies range of 6.8 to 8.2 MeV in ²⁶Si and 2.3 to 3.8 MeV in ²⁷P were scanned, respectively. Several resonances above the proton threshold level were observed with high statistics and free from any background contribution in the target. Their resonance parameters were subsequently extracted by an R-matrix analysis; these are important to better constrain the production rates of the ²⁵Al(p,γ)²⁶Si and ²⁶Si(p,γ)²⁷P reactions.

The ³⁰S(α,p) reaction is considered to be important in the nuclear trajectory to higher mass in type I X-ray bursts. The reaction flow encounters a bottle-neck at ³⁰S, owing to the competition of photo-disintegration with further proton capture, and because the half-life of this isotope is on the order of the burst rise timescale. Different burst simulations by various researchers indicate the (α,p) reaction may by-pass this waiting point, depending on the stellar reaction rate, which has not previously been measured experimentally, and the structure of the compound nucleus ³⁴Ar is not well understood above the alpha-threshold. The ³⁰S(α,p) reaction could explain rare bolometrically double-peaked burst profiles, appears to make a considerable contribution to the overall energy generation, and affects the neutron star crustal composition for the recurrent inertia required in burst models to reproduce astronomical observations. Using a low-energy ³⁰S radioactive ion beam and an active target technique (a helium gas mixture serves as both a target gas and a detector fill gas), we acquired data on both alpha elastic scattering of ³⁰S as well as the ³⁰S(α,p) reaction simultaneously at relevant energies for X-ray bursts. We present for the first time the status of the data analysis and the preliminary results of this research.

Astrophysical stellar reactions at extremely high temperatures involve a variety of problems both in nuclear reactions and nuclear structures. Specifically, the problems in the νpprocess were discussed in this talk based on our recent experimental results with low-energy RI beams and a simulation study. The νp-process is one of the key processes for investigating the mechanism of type II supernovae, and the process could be possibly responsible for ”the excess production” of p-nuclei around mass 90-100. Alpha cluster resonances have been discovered experimentally to play a crucial role for the stellar (α, p) reactions just above the alpha threshold. Neutron induced reactions in the proton-rich nuclear regions in the νp-process are also suggested to play an important role, which involve nuclear structures of high level density at high excitation energies, probably giant resonances. The discussion also covered the p-nuclei production through the νp-process at around mass 100.

Nucleosynthesis by alpha particles and heavier 4n nuclei are of great interest as they would involve nuclear cluster resonances. The role of nuclear clustering is discussed for nucleosynthesis with the Cluster Nucleosynthesis Diagram (CND) proposed before, especially those involving alpha induced reactions, based on our recent works of (α,p) reactions with low energy RI beams. We present experimental results that alpha resonances play a crucial role for the (α,p) reaction cross sections. Molecular resonances are also briefly discussed along this line for O- and C-burning.

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.

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.

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.

CRIB (CNS Radioactive Ion Beam separator) is a low-energy RI beam separator at 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 ⁷Be+α resonant scattering is presented.

The ¹⁸Ne(α, p)²¹Na reaction is thought to be one of the key breakout reaction from the hot CNO cycle to the rp-process in X-ray bursts. We investigated the resonant properties of the compoundnucleus ²²Mg by measuring the resonant elastic scattering of ²¹Na+p. An 89 MeV ²¹Na radioactive beam was produced by CRIB and then bombarded a 93-μm-thick polyethylene target. The ²¹Na beam intensity was about 2×10⁵ pps, with a purity of about 70% on the target. The recoiled protons were measured by three sets of ΔE-E telescope respectively. A wide excitation energy range of 5.5-9.2 MeV in ²²Mg was scanned with a thick-target method. Some preliminary results are shown.

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.

The astrophysically important states in ²⁶Si have been studied with different reactions because of their dominant contribution to the ²⁵Al(p,γ)²⁶Si reaction rate at nova temperatures. We performed two different experiments to study the states of interest in ²⁶Si, with the aim of reducing the main uncertainty in the current ²⁵Al(p,γ)²⁶Si rate by determining the level parameters of the dominant states more accurately. One is the p(²⁷Si,²⁶Si^*)d experiment at NSCL, in which we measured the gamma-ray decays from the excited states in ²⁶Si. The other one is the ²⁵Al+p elastic scattering experiment with CRIB at RIKEN.

The first direct measurement of the ¹¹C(α, p)¹⁴N reaction cross section of astrophysical interest has been performed for the center-of-mass energies from 1 to 4.5 MeV with the CRIB (Center for Nuclear Study Radioactive Ion Beam separator). We successfully distinguished the transition to the ground state of ¹⁴N and that to the second excited state with a comparable yield. The resonant shapes in the preliminary excitation function for the ground state transition have been confirmed to be consistent with the ones from the time-reversal reaction data of previous experiments.

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(α, p) stellar reaction rate within the Gamow window of Type I X-ray bursts.

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 to extrapolate the ³⁰S(α,p) stellar reaction rate within the Gamow window of Type I X-ray bursts. The importance of the ³⁰S(α,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.

The role of nuclear clustering is discussed for nucleosynthesis in stellar evolution with Cluster Nucleosynthesis Diagram (CND) proposed before. Special emphasis is placed on α-induced stellar reactions together with molecular states for O and C burning.

Nuclear astrophysics activities with CNS RI beam separator (CRIB) are reported together with the present status of the CRIB facility which is supported by the AVF upgrade project for the total development of the low-energy RIB facility. The activities include direct and indirect measurements of stellar reactions especially relevant to explosive burning processes such as nova and supernovae. Some recent results are discussed together with a scope of the facility.

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. 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.

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 resonant scattering is 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 radioisotope ²⁶Al is an important probe of the interstellar medium of our galaxy, but its production is now still not well determined partially due to the lack of knowledge of the important states in ²⁶Si, which dominate the large uncertainty in the ²⁵Al(p,γ)²⁶Si reaction rate at nova temperatures. We give an update on two experiments that were performed to study these states. One is a measurement of the ²⁷Si(p,d)²⁶Si^* reaction at the NSCL, and the other one is a measurement of the ²⁵Al+p elastic scattering with the CRIB facility at RIKEN.

The present work reports the results of ³⁰S radioactive beam development for a future experiment directly measuring data to extrapolate the ³⁰S(α,p) stellar reaction rate in Type I X-ray bursts, a phenomena where nuclear explosions occur repeatedly on the surface of accreting neutron stars. We produce the radioactive ion ³⁰S via the ³He(²⁸Si,³⁰S)n reaction, by bombarding a cryogenically cooled target of ³He at 400 Torr and 80 K with ²⁸Si beams of 6.9 and 7.54 MeV/u. In order to perform a successful future experiment which allows us to calculate the stellar ³⁰S(α,p) reaction rate, Hauser-Feshbach calculations indicate we require a ³⁰S beam of ~10⁵ particles per second (pps) at ~ 32 MeV. Based on our recent beam development experiments in 2006 and 2008, it is believed that such a beam may be fabricated in 2009 according to the results presented. We plan to measure the ⁴He(³⁰S,p) cross-section at astrophysical energies in 2009, and some brief remarks on the planned (α,p) technique are also elucidated.

The understanding of energy generation in Type I X-ray bursts will be enhanced by a direct measurement of the nuclear reaction cross section ³⁰S(α,p)³³Cl. Models of this explosive stellar nucleosynthesis are constrained by the observations of bursts with multiple peaks in their bolometric luminosity. A recent model by Fisker, Thielemann, & Wiescher (2004) gives a theoretical basis for a nuclear waiting point at ³⁰S in order to explain these observations. In order to experimentally test the predictions of this model, the authors undertook two days of ³⁰S radioactive ion beam (RIB) development in December 2006 in preparation for a 2008 experiment directly measuring the α(³⁰S,p) cross section.

In the first half of the paper, the nuclear astrophysics activities in Japan, especially in experimental studies are briefly overviewed. A variety of beams have been developed and used for nuclear astrophysics experiments in Japan. The activities include the RI beam facilities at low energies by the in-flight method at the Center for Nuclear Study (CNS), University of Tokyo and by the ISOL-based method at the JAERI tandem facility, and the RI beam facility at intermediate energies at RIKEN. Other activities include a study of the ¹²C(α,γ)¹⁶O reaction exclusively at the tandem accelerator at the Kyushu University, and studies at the neutron facility at Tokyo Institute of Technology and at the photon facility at AIST (Sanso-ken). Research opportunities in the future at RIBF, J-PARC, and SPRING8 are also discussed. A discussion on the research activities at CNS has been specifically extended in the latter half, including various possibilities in collaboration at the RI beam factory at RIKEN.

Radioactive-ion (RI) beams of ¹⁰C, ¹⁴O, ^12N and ¹¹C with energies low 10 A MeV were produced by using a low-energy in-flight RI beam separator newly constructed by CNS, University of Tokyo. Using the ¹²N and ¹¹C beams, some resonance states were identified in the proton elastic scattering ¹²N+p and ¹¹C+p, respectively.

Proton resonant states in ²⁷P have been studied by the resonant elastic scattering of ²⁶Si+p with a ²⁶Si radioactive ion beam at 3.039 MeV/u bombarding a thick H2 gas target with the inverse kinematics method at the low-energy RI beam facility CRIB at CNS, University of Tokyo. The properties of these resonance states are important to better determine the production rates of ²⁶Si(p,γ)²⁷P reaction which is one of the atrophysically important reactions to understand the production of the ground state of ²⁶Al under the explosive stellar environments at higher temperature. In this work, some new states have been observed with a high statistics and background free through a covered the range of excitation energies from Ex = 2.3 to 3.8 MeV. The resonant parameters of those states, were determined by an R-matrix analysis of the excitation functions.

Nucleosynthesis of ²²Na is an interesting subject because of possible γ-ray observation and isotopic anomalies in presolar grain. ²²Na would have been mainly produced in the NeNa cycle. At high temperature conditions, ²¹Na(α,p)²⁴Mg reaction could play a significant role to make flow from the NeNa cycle to the next MgAl cycle and beyond. Clearly, the ²¹Na(α,p)²⁴Mg stellar reaction would bypass ²²Na, resulting in reduction of ²²Na production, therefore, it is strongly coupled to the Ne-E problem. It could be also important to understand the early stage of the rp-process. Experiment was performed using a 39 MeV ²¹Na radioactive beam obtained by the CNS Radio Isotope Beam separator CRIB of the University of Tokyo. Both protons and alphas were measured from α+²¹Na scattering with a thick ⁴He gas target.

The ¹⁴O(α, p)¹⁷F stellar reaction is one of the key reactions for the breakout from the Hot--CNO cycle to the rp--process. Since the cross sections depends on the product of α and proton widths of the intermediate states in ¹⁸Ne, it is important to determine these widths. We performed an experiment of the ¹⁴O + α scattering with a thick target method at the CNS Radioactive Ion Beam (CRIB) facility. The experiment was carried out using a thick Helium gas target and position sensitive silicon telescopes. This measurement provides an excitation function of ¹⁴O + α scattering for an energy range of E_cm = 1.7 -- 5.9 MeV. We will concentrate on the elastic scattering channel in this presentation, since the α-cluster structure in ¹⁸Ne above the α--threshold would play an important role for the stellar reaction. Several α--resonances were observed in the present experiment. The experimental result will be presented, and the α cluster structure in ¹⁸Ne and the significance to the stellar reaction will be discussed.

A recent simulation of the rp-process in neutrino-driven winds in type II supernovae (νp-process) suggests that the ¹¹C(α,p)¹⁴N reaction could be an important breakout pass from the pp-chain region to the CNO region. However, there are only very limited experimental information of the reaction cross section available from the time-reverse reaction studies. In order to determine the reaction rate of ¹¹C(α,p)¹⁴N, a direct measurement by means of the thick-target inverse-kinematics method has recently been performed using low-energy ¹¹C beams from the CNS Radioactive Ion Beam (CRIB) separator, a ⁴He gas target and δE-E position-sensitive silicon telescopes at three downstream angles. The experiment covered E_CM = 0.5--5 MeV corresponding to the stellar temperature of 1.5--7 GK. The obtained reaction cross section including some resonances and transitions to the excited states of ¹⁴N will be reported.

For the rapid proton capture process (rp-process) in X-ray bursts and the core-collapse stage of supernovae, proton-rich pf-shell nuclei far from the line of stability play important roles. Studies of the feeding ratios and half-lives of the β and electron capture decays of these proton-rich pf-shell nuclei are of great astrophysical interest not only for nucleo synthesis but also for Fermi and Gamow-Teller transition study. The experiment to measure the half life of β decay of ⁴⁶Cr was performed using the low-energy RI beam separator (CRIB) of the Center for Nuclear Study (CNS), University of Tokyo. The ⁴⁶Cr particles were produced by the ³⁶Ar + ¹²C fusion reaction. A natural C foil of 0.56 mg/cm² was installed as the primary target. The ³⁶Ar primary beam was accelerated up to 3.6 MeV/nucleon by the RIKEN AVF cyclotron. A double sided Si strip detector (DSSD) of 500-μm thickness was used as a β-ray detector. A Si detector of 1.5-mm thickness was placed just behind the DSSD for a β-ray detector. To measure β-delayed γ rays, 3 clover and 1 coaxial Ge detectors were set around the target chamber. The beam was pulsed to measure the half life of the β decay of ⁴⁶Cr. The β-delayed γ ray of ⁴⁶Cr was observed in this experiment. The experimental result will be discussed.