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The M1 strengths (or level density of 1+ states) are of importance for estimation of interaction strengths between neutrinos and nuclei for the study of the supernova neutrino-process. In 1957, Agodi predicted theoretically angular distribution of neutrons emitted from states excited via dipole transitions with linearly polarized gamma-ray beam at the polar angle of θ=90° should be followed by a simple function, a + b cos(2ɸ), where ɸ is azimuthal angel. However, this theoretical prediction has not been verified over the wide mass region except for light nuclei as deuteron. We have measured neutron angular distributions with (polarized gamma, n) reactions on Au, NaI, and Cu. We have verified the Agodi's prediction for the first time over the wide mass region. This suggests that (polarized gamma, n) reactions may be useful tools to study M1 strengths in giant resonance regions. [ABSTRACT FROM AUTHOR]

Almost half of heavy nuclei beyond iron are considered to be produced by rapid neutron capture process (r-process). This process occurs in the neutron-rich environment such as core-collapse supernovae or neutron star mergers, but the main production site is still unknown. In the r-process of neutron star mergers, nuclear fission reactions play an important role. Also beta-decay half-lives of magic nuclei are crucial for the r-process. We have carried out r-process nucleosynthesis calculations based upon new theoretical estimates of fission fragment distributions and new beta-decay half-lives for N=82 nuclei measured at RIBF-RIKEN. We investigate the effect of nuclear fission on abundance patterns in the matter ejected from neutron star mergers with two different fission fragment mass distributions. We also discuss how the new experimental beta-decay halflives affect the r-process. [ABSTRACT FROM AUTHOR]

We have measured the γ-ray angular distribution of the 12C(α,γ)16O reaction at TRIAC (Tokai Radioactive Ion Accelerator Complex) to accurately determine the E1 and E2 cross sections. In this experiment, we used high efficiency anti-Compton NaI(T1) spectrometers to detect a γ-ray from the reaction with large S/N ratio, intense pulsed α-beams to discriminate true event from background events due to neutrons from 13C(α,n)16O reaction with a time-of-flight (TOF) method. We succeeded in removing a background events due to neutrons and clearly detected γ-ray from the 12C(αγ)16O reaction with high statistics. [ABSTRACT FROM AUTHOR]

To treat heavy-ion reactions using actinide target nucleus, we propose a model which takes into account the coupling to the collective states of interacting nuclei in the penetration of the Coulomb barrier and the dynamical evolution of nuclear shape from the contact configuration. A fluctuation-dissipation model (Langevin equation) was applied in the dynamical calculation, where effect of nuclear orientation at the initial impact on the prolately deformed target nucleus was considered. Using this model, we analyzed the experimental data for the mass distribution of fission fragments (MDFF) in the reaction of 36S+238U at several incident energies. Fusion-fission, quasifission and deep-quasi-fission are separated as different trajectories on the potential energy surface. We estimated the fusion cross section of the reaction. [ABSTRACT FROM AUTHOR]

The few-body, especially three-body, problem is still an open (and therefore interesting) subject in nuclear physics, and has been studied intensively by various theoretical frameworks. The n+6Li reactions are important not only from the basic interest but also from the application point of view. The 6Li nucleus is well described by the cluster model such as α+d and α+p+n. Therefore, it is necessary for us to treat the n+6Li system with α+d+n and α+p+n+n models. In this work, we study the n+6Li inelastic reactions applying the α+d cluster model to 6Li and using the continuum-discretized coupled-channels approach. We have included elastic and inelastic data at 14.1 MeV neutron incident energies in the calculation. At the present energy, our calculation gives almost good agreement with experimental data. [ABSTRACT FROM AUTHOR]

Cross sections of 12,13C are evaluated for both neutrons and protons with incident energies up to 3 GeV. The evaluation is based on predictions from nuclear-model calculations and systematics as well as measurements. A nuclear-model calculation-code system is developed using the GNASH code for energies less than 150 MeV and the JQMD code for those above 150 MeV. The evaluated cross sections are as follows; neutron total cross sections, nucleon elastic scattering cross sections and angular distributions, nonelastic cross sections, production cross sections and double-differential cross sections of secondary light particles (n, p, d, t, 3He, α, and π) and gamma-rays, and isotope-production cross sections. The results are compared with available experimental data and the other evaluation. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

An overview is presented of recent nuclear data evaluations performed for the JENDL high-energy (JENDL-HE) file, in which neutron and proton cross sections for energies up to 3 GeV are included for the whole 132 nuclides. The current version of the JENDL-HE file consists of neutron total cross sections, nucleon elastic scattering cross sections and angular distributions, nonelastic cross sections, production cross sections and double-differential cross sections of secondary light particles (n, p, d, t, 3He, α, and π) and gamma-rays, isotope production cross sections, and fission cross sections in the ENDF6 format. The present evaluations are performed on the basis of experimental data and theoretical model calculations. For the cross section calculations, we have constructed a hybrid calculation code system with some available nuclear model codes and systematics-based codes, such as ECIS96, OPTMAN, GNASH, JQMD, JAM, TOTELA, FISCAL, and so on. The evaluated cross sections are compared with available experimental data and the other evaluations. Future plans of our JENDL-HE project are discussed along with prospective needs for high-energy cross section data. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Nucleon-induced cross sections on magnesium isotopes, 24,25,26Mg, and silicon isotopes, 28,29,30Si, were evaluated for energies up to 3 GeV. Evaluation of nucleon-scattering cross sections was performed by a consistent analysis of nuclear-level structure and nucleon-scattering data using a unified framework of a soft-rotator model and coupled-channel approach. The scattering cross sections for silicon isotopes were re-analyzed based on two new considerations. First the silicon isotopes were assumed to be deformed nuclei having oblate shapes, second the more sophisticated form of optical-potential energy dependence was used. The evaluation of the particle emissions was performed by using a nuclear-model code system consisting of the GNASH code up to 150 MeV and the JQMD code above 150 MeV. The present results were compared with available experimental data and the LA 150 evaluation. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Universal baryon-density parameter ΩB inferred from the Big-Bang nucleosynthesis and cosmic microwave background fluctuations disagrees with each other at the 1σ level. We propose new cosmological models for the Big-Bang nucleosynthesis to try to recover the concordance of ΩB. Nuclear processes in the Big-Bang nucleosynthesis are similar to those in the r-process nucleosynthesis in supernovae. Even in the nucleosynthesis of heavy elements, entropy and density in the neutrino-driven winds of Type II supernovae are so high that nuclear statistical equilibrium favors production of abundant light nuclei. In such explosive circumstances many radioactive light-to-intermediate mass nuclei as well as heavy mass nuclei play the significant roles. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

About half of heavy elements are considered to be produced by the rapid neutron-capture process, r-process. The neutron star merger is one of the viable candidates for the astrophysical site of r-process nucleosynthesis. Nuclear fission reactions play an important role in the r-process of neutron star mergers. However theoretical predictions about fission properties of neutron-rich nuclei have some uncertainties. Especially, their fission fragment distributions are totally unknown and the phenomenologically extrapolated distribution was often applied to nucleosynthesis calculations. In this study, we have carried out r-process nucleosynthesis calculations based upon new theoretical estimates of fission fragment distributions. We discuss the effects on the r-process in neutron star mergers from the nuclear fission of heavy neutron-rich actinide elements. We also discuss how variations in the fission fragment distributions affect the abundance pattern. [ABSTRACT FROM AUTHOR]

Multi-modal fission has been systematically investigated for the series of isotopes of Fm and Cf. The multi-dimensional Langevin-type stochastic differential equation is used for the dynamical calculation. The primary fission mode changes from mass-asymmetric fission to mass-symmetric fission with the increase of neutron numbers for both Fm and Cf cases. [ABSTRACT FROM AUTHOR]

Neutrino-nucleus reactions induced by supernova neutrinos are investigated for 12C and 4He. Both of charge-exchange and neutral current processe are treated. Branching ratios to various decay channels are calculated by the Hauser-Feshbach theory taking into account the levels excited by ν’s with a specific isospin and residual ones assuming isospin conservation. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The three-charged-particle Faddeev-type equations for a full potential system are presented in momentum space. The potential is composed of a short range two-body, nuclear potential and a three-body-force potential plus the long range Coulomb potential. A novel framework is proposed for this purpose which contains two innovations aimed at realizing a breakthrough for the notoriously troublesome long range behavior of charged particle systems and tedious Coulomb prescriptions in momentum space calculations. One involves introduction of a Coulomb boundary condition and the other is a new definition of the Coulomb amplitude using two-potential theory for VC = VR + V[lowercase_phi_synonym] with respect to a screened Coulomb potential VR and the remainder V[lowercase_phi_synonym] = VC - VR. Some important equations, which are underlined in our approach, are mathematically proved. The formulation is not only rigorous but also useful for numerical calculations. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]