Search

Experimental results from the J-PARC E13 experiments are summarized. A new experimental set up of E13 has established a platform for the future γ-ray hypernuclear spectroscopy at J-PARC using kaon beams. New γ rays are identified in 4ΛHe and 19Λ F. The energy of 1.406 MeV for the 4ΛHe(1+→0+) transition confirmed a sizable effect of Charge Symmetry Breaking (CSB) in ΛN interaction in the A=4 hypernuclear system. The identification of four γ rays in 19Λ F is made for the first time in sd shell hypernuclei. Especially, energy spacing of the ground state doublet is found to be 315.5 keV. A good agreement with two theoretical calculations suggests that the theoretical formalism used in p shell hypernuclei is also applicable to heavier hypernuclei. Lastly, an overview of the future J-PARC E63 experiment is given. [ABSTRACT FROM AUTHOR]

The Σp scattering experiment has just been started at J-PARC this year (2018). We made ”Σ beam factory” a reality where a beam with an intensity of more than 5 × 105 Σ− beam per day could be produced by using 20 M/spill π− beam. The CATCH system, which is a dedicated system to detect recoil proton from the Σp scattering, operated stably under the high counting rate, and its successful operation was confirmed by identifying the pp scattering events in J-PARC. In the June beam time, the production run of the Σ− p scattering was carried out for 2 days, which was just 10% of the requested beam time. The remaining beam time of the Σ− p channel and the Σ+ p channel will take place in the spring of 2019. [ABSTRACT FROM AUTHOR]

An experiment was performed by means of Trojan Horse Method (THM) at the LNS Tandem in Catania. The investigation of the relevant 19F(p,α)16O two-body reaction was performed by selecting the quasi free (QF) contribution of the 19F(²H,α16O)n three-body reaction, using the deuteron target as TH nucleus. The aim of this measurement is to obtain the 19F(p,α)16O cross section. The experimental set-up and the calibration of the detectors will be presented. [ABSTRACT FROM AUTHOR]

The 12C(12C,α0,1)20Ne and 12C(12C,p0,1)23Na reactions have been measured from Ec.m.=2.7 MeV down to 0.8 MeV via the Trojan Horse Method o the deuteron in 14N. This range of energies is relevant in astrophysical scenarios, from superburst ignition to explosive stellar carbon burning. The deduced astrophysical S(E) factors exhibit several resonances that are responsible for a very large increase of the reaction rate at the relevant temperatures. [ABSTRACT FROM AUTHOR]

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 Qvalue spectra shows the evidence of the three-body channels of interest. We confirmed that 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 SE1(300) and 7 to 120 keVb for SE2(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. [ABSTRACT FROM AUTHOR]

Novae are astrophysical events (violent explosion) occurring in close binary systems consisting of a white dwarf and a main-sequence star or a star in a more advanced stage of evolution. They are called "narrow systems" because the two components interact with each other: there is a process of mass exchange with resulting in the transfer of matter from the companion star to the white dwarf, leading to the formation of this last of the so-called accretion disk, rich mainly of hydrogen. Over time, more and more material accumulates until the pressure and the temperature reached are sufficient to trigger nuclear fusion reactions, rapidly converting a large part of the hydrogen into heavier elements. The products of "hot hydrogen burning" are then placed in the interstellar medium as a result of violent explosions. Studies on the element abundances observed in these events can provide important information about the stages of evolution stellar. During the outbursts of novae some radioactive isotopes are synthesized: in particular, the decay of short-lived nuclei such as 13N and 18F with subsequent emission of gamma radiation energy below 511 keV. The gamma rays from products electronpositron annihilation of positrons emitted in the decay of 18F are the most abundant and the first observable as soon as the atmosphere of the nova starts to become transparent to gamma radiation. Hence the importance of the study of nuclear reactions that lead both to the formation and to the destruction of 18F. Among these, the 18F(p, α)15O reaction is one of the main channels of destruction. This reaction was then studied at energies of astrophysical interest. The experiment done at Riken, Japan, has as its objective the study of the 18F(p, α)15O reaction, using a beam of 18F produced at CRIB, to derive important information about the phenomenon of novae. In tis paper we present the experimental technique and the Monte Carlo code developed to be used in the data analysis process. [ABSTRACT FROM AUTHOR]

The lecture includes two parts: One is a discussion on the technology for developing RIB beam facility based on the in-flight method and relevant experimental technology. The second part is a discussion on experimental efforts for studying the breakout process from the pp-chain region based on recent works with low energy RI beams. The discussion of the second part specifically covers the problem of the vp-process in type II supernovae in terms of alpha cluster nature for the reactions. [ABSTRACT FROM AUTHOR]

Several alpha-induced astrophysical reactions have been studied 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. One of the methods to study them is the α resonant scattering using the thick-target method in inverse kinematics. Among the recent studies at CRIB, the measurement of 7Be+α resonant scattering is discussed. Based on the result of the experiment, we evaluated the contributions of high-lying resonances for the 7Be(α, ã ) reaction, and proposed a new cluster band in 11C. [ABSTRACT FROM AUTHOR]

Two reactions of 14O(α,p)17F and 18Ne(α,p)21Na provide the pathways for breakout from the hot CNO cycles to the rp-process in type I X-ray bursts. To better determine their astrophysical reaction rates, resonance parameters of the compound nuclei 18Ne and 22Mg have been investigated by the resonant elastic scattering of 17F+p and 21Na+p, respectively. The 17F and 21Na radioactive ion beams were produced at the CNS Radioactive Ion Beam Separator and impinged on the thick proton targets. The excitation functions were obtained with a thick-target method over a wide excitation energy range. The resonance parameters in the compound nuclei 18Ne and 22Mg have been determined through an R-matrix analysis. New reaction rates of these two (α,p) reactions are recalculated. The astrophysical impact for the 18Ne(α,p)21Na reaction has been investigated through one-zone postprocessing X-ray burst calculations. [ABSTRACT FROM AUTHOR]

The abundance of 18F in Nova explosions is considered to be an important piece of information for the understanding of this astrophysical phenomenon. It is then necessary to study the nuclear processess that both produce and destroy this isotope in Novae. Among these latter reactions, the 18F(p,á)15O is one of the most important 18F destruction channels. Here we report on an experiment performed using the CRIB apparatus of the Center for Nuclear Study of the University of Tokyo. This was the first experiment that used the Trojan Horse method applied to a Radioactive Ion Beam induced reaction. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Shell gap at the magic number N = 82 is important to reproduce the 2nd peak of r-process abundance. If a spin-orbit force is reduced in a very neutron-rich region, a shell quenching at N = 82 and a new shell closure at N = 70 are predicted. A shell evolution by the spin-orbit-force reduction can be searched for through the shape evolution of Zr isotopes around an expected double magic nuclei, 110Zr(Z = 40,N = 70). We performed β-γ and isomer spectroscopy at RIBF to observe low-lying states in 106,108Zr. The present results indicate a well deformed shape for 106,108Zr. The drastic reduction of the spin-orbit force most likely does not occur around 110Zr on an r-process path. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The abundance of 18F in Nova explosions is an important issue for the understanding of this astrophysical phenomenon. For this reason it is necessary to study the nuclear reactions that produce or destroy this isotope in novae. Among these latter processes, the 18F(p,α)15O is one of the main 18F destruction channels. We report here on the preliminary results of the first experiment that applies the Trojan Horse Method to a Radioactive Ion Beam induced reaction. The experiment was performed using the CRIB apparatus of the Center for Nuclear Study of The Tokyo University. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]