ランタン(La)-139の断面積と共鳴パラメータは、原子力分野への応用や基礎核物理の研究にとって重要である。本論文では、大強度陽子加速器施設(J-PARC)のANNRIにてLaの中性子全断面積と捕獲断面積を測定した。Negative共鳴を含む4つの共鳴の共鳴パラメータを、共鳴解析コードREFITを用いて求めた。その結果いくつかの共鳴パラメータにおいて、評価済み核データライブラリとの不一致が見られた。さらに全断面積を再現するために、スピン依存する散乱半径もフィットした。得られた散乱半径は、評価済み核データライブラリで記録されたものよりも大きいことがわかった。

A neutron filtering system has been designed and implemented in the Accurate Neutron-Nucleus Reaction Measurement Instrument (ANNRI) beamline in the Materials and Life Science (MLF) facility of the Japan Proton Accelerator Research Complex (J-PARC) to bypass the effect of the double-bunch mode of JPARC by molding the incident neutron flux into quasi-monoenergetic neutron beams. Filter assemblies using Fe, Si and Cr as filter materials were analyzed by means of experimental analysis, together with Monte Carlo simulations. The characteristics of the filtered neutron beam are presented and discussed alongside its viability in future applications for neutron cross-section measurements in the keV neutron region.

Japanese Evaluated Nuclear Data Library version 5 (JENDL-5) was released in 2021. JENDL-5 is intended to extend its generality from JENDL-4.0 by covering a wide variety of nuclear data for applications not only to nuclear design and decommissioning, but also to radiation-related fields. Overview of JENDL-5 and a future plan for the next of JENDL-5 are presented. JENDL-5 includes up-to-date neutron reaction cross sections incorporating other various types of data such as newly evaluated nuclear decay, fission yield, and thermal neutron scattering law. The neutron induced reaction cross sections especially on minor actinides in the resonance regions are improved by the experimental data measured at ANNRI. The extensive benchmark analyses on neutron nuclear data were made and the performance of JENDL-5 was confirmed by benchmark tests of ICSBEP and IRPhEP as well as fast reactors, radiation shielding calculations, and so on. So far, several JENDL special-purpose files have been developed for various applications. The data cover neutron, charged particles, and photon induced reactions. As the neutron induced reaction files, two special purpose files of JENDL/AD-2017 and JENDL/ImPACT-2018 were released to meet needs of nuclear backend applications including activation evaluation for nuclear facilities and nuclear transmutations of high-level radioactive wastes of long-lived fission products, respectively. Furthermore, the photon, proton and deuteron data were released as JENDL/PD-2016.1, JENDL-4.0/HE and JENDL/DEU-2020, respectively, for accelerator applications. With updating the data, they were incorporated in JENDL-5 as sub-libraries for facilitation of usability of JENDL. As the next step of JENDL-5, we are planning to provide the proper and sufficient covariance data that will contribute to uncertainty estimation in various applications.

The neutron capture cross sections of Cm-244 and Cm-246 were measured for the neutron energy range of 1-1000 eV via the neutron time-of-flight method with Accurate Neutron-Nucleus Reaction measurement Instrument (ANNRI) at Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). The world's most intense neutron pulses from the Japan Spallation Neutron Source (JSNS) enable the accurate measurement of neutron capture cross sections. Besides, single-bunched neutron pulses allow the analysis in a higher neutron energy region than the previous measurement at ANNRI. The resonance analyses were performed up to 1000 eV by using a resonance shape analysis code REFIT. The spectra of prompt gamma-rays from neutron capture reactions of Cm-244 and Cm-246 were also obtained, and 43 and 10 prompt gamma-ray peaks from Cm-244 (n, gamma) and 246Cm (n, gamma) reactions were newly observed, respectively.

Natural gadolinium is widely used for its excellent thermal neutron capture cross section, because of its two major isotopes: Gd-155 and Gd-157. We measured the gamma-ray spectra produced from the thermal neutron capture on targets comprising a natural gadolinium film and enriched Gd-155 (in Gd2O3 powder) in the energy range from 0.11 MeV to 8.0 MeV, using the ANNRI germanium spectrometer at MLF, J-PARC. The freshly analyzed data of the Gd-155(n,gamma) reaction are used to improve our previously developed model (ANNRI-Gd model) for the Gd-157(n,gamma) reaction [K. Hagiwara et al. [ANNRI-Gd Collaboration], Prog. Theor. Exp. Phys. 2019, 023D01 (2019)], and its performance confirmed with the independent data from the Gd-nat(n,gamma) reaction. This article completes the development of an efficient Monte Carlo model required to simulate and analyze particle interactions involving the thermal neutron captures on gadolinium in any relevant future experiments.

Neutron capture and total cross sections of Gd-155 and Gd-157 were measured with the neutron time of-flight method in Accurate Neutron-Nucleus Reaction measurement Instrument at Material and Life Science Experimental Facility of the Japan Proton Accelerator Research Complex using the NaI (Tl) spectrometer and Li-glass detectors. Preliminary cross sections were obtained in the neutron energy region from 4 meV to 100 meV. The derived cross sections agree with evaluated values in JENDL 4.0 and the experimental results by Mastromarco but were not consistent with those by Leinweber.

A research project entitled "study on accuracy improvement of fast-neutron capture reaction data of long-lived MAs for development of nuclear transmutation systems" is ongoing as a joint collaboration, including Tokyo Tech, Japan Atomic Energy Agency and Kyoto University in Japan. This project focuses on neutron capture reaction of minor actinides ²³⁷Np, ²⁴¹Am and ²⁴³Am, in the fast neutron energy region. The final goal of this project is to improve the neutron capture cross sections utilizing a high-intensity neutron beam from a spallation neutron source of the Japan Proton Research Complex. The overview of the project and the current progress are presented.

In order to develop an evaluation method of gamma-ray strength function (GSF), neutron capture pulse-height (PH) spectrum of gold was employed, where it was measured with the NaI(Tl) spectrometer of AN-NRI installed at the Material and Life Science Experimental Facility in J-PARC. The neutron capture gamma-ray spectrum of gold was calculated using the nuclear reaction model code CCONE. In order to obtain the information on GSF from the measured data, a gamma-ray response function for the NaI(Tl) spectrometer was calculated by the Monte-Carlo particle-transport simulation code PHITS. As a result, the PH spectrum comparable with measured one was derived by applying the gamma-ray response function to the calculated gamma-ray spectrum. By evaluation with measured PH spectra, we obtained GSF which reasonably explains measured PH spectrum in the continuum region.

© 2019, © 2019 Atomic Energy Society of Japan. All rights reserved. A new nuclear data library, JENDL/ImPACT-2018, was developed for an innovative study on the transmutation of long-lived fission products. Nuclear reaction cross-sections were newly evaluated for incident neutrons and protons up to 200 MeV for 163 nuclides focusing on long-lived nuclei such as 79Se, 93Zr, 107Pd and 135Cs, adopting some parts of JENDL-4.0. Our challenge was an evaluation of cross-sections for a number of unstable nuclei over a wide energy range where the experimental data were very scarce. We estimated cross-sections based on a nuclear model code CCONE by incorporating an advanced knowledge on the nuclear structure theory and a model-parameterization based on new experimental cross-sections measured by the inverse kinematics. Through comparisons with available experimental data on the stable isotopes, it is found that the present data give better agreements with them than those in the existing libraries. In a neutronics simulation by the PHITS code, we also found that the largest impact of the present library was seen on the estimated amount of isotope productions.

The importance of a good model for the g-ray energy spectrum from the radiative thermal neutron capture on Gadolinium (Gd) is specially increased in the present era of Gd-enhanced &amp
macr
ne-search detectors. Its an essential prerequisite for MC studies to evaluate the neutron tagging efficiency, in order to enhance signal sensitivity in the Gd-loaded &amp
macr
ne-search detectors. The g-ray spectra produced from the thermal neutron capture on enriched gadolinium targets (155Gd, 157Gd and Natural Gd) in the energy range 0.11 MeV to 8.0 MeV, were measured using the ANNRI Germanium Spectrometer at MLF, J-PARC. Based on the data acquired and a GEANT4 simulation of the ANNRI detector, we reported the energy spectrum of 157Gd(n, g) and developed a g-ray emission model of 157Gd(n, g) in our previous publication. We now present the analysed data of 155Gd(n, g) and natGd(n, g) reactions, the energy spectra of g-rays and an improved model for 155Gd(n, g), 157Gd(n, g) and natGd(n, g) reactions. The consistency of the results from the devised model is checked among all the 14 germanium crystals, at the level of 15% spectral shape deviation at 0.2 MeV binning.

The dipole strength distribution of Pb-206 was investigated via a nuclear resonance fluorescence experiment using bremsstrahlung produced with an electron beam at a kinetic energy of 10.5 MeV at the linear accelerator ELBE. We identified 88 states resonantly excited at energies from 3.7 to 8.2 MeV. The analysis of the measured gamma-ray spectra includes the quasicontinuum of levels at high energy. Monte Carlo simulation of gamma-ray cascades were performed to obtain the intensities of inelastic transitions and branching ratios of the ground-state transitions. The extracted photoabsorption cross section shows enhanced dipole strength at the excitation energies around 5.5 and 7 MeV, which may related to a pygmy dipole resonance. The present (gamma, gamma') data combined with (gamma, n) data from the literature were used for confining input parameters of the statistical calculation code CCONE to derive the neutron-capture cross section of the unstable Pb-205 nucleus.

We have measured the $\gamma$-ray energy spectrum from the thermal neutron<br />
capture, ${}^{157}$Gd$(n,\gamma){}^{158}$Gd, on an enriched $^{157}$Gd target<br />
(Gd$_{2}$O$_{3}$) in the energy range from 0.11 MeV up to about 8 MeV. The<br />
target was placed inside the germanium spectrometer of the ANNRI detector at<br />
J-PARC and exposed to a neutron beam from the Japan Spallation Neutron Source<br />
(JSNS). Radioactive sources ($^{60}$Co, $^{137}$Cs, and $^{152}$Eu) and the<br />
reaction $^{35}$Cl($n$,$\gamma$) were used to determine the spectrometer&#039;s<br />
detection efficiency for $\gamma$ rays at energies from 0.3 to 8.5 MeV. Using a<br />
Geant4-based Monte Carlo simulation of the detector and based on our data, we<br />
have developed a model to describe the $\gamma$-ray spectrum from the thermal<br />
${}^{157}$Gd($n$,$\gamma$) reaction. While we include the strength information<br />
of 15 prominent peaks above 5 MeV and associated peaks below 1.6 MeV from our<br />
data directly into the model, we rely on the theoretical inputs of nuclear<br />
level density and the photon strength function of ${}^{158}$Gd to describe the<br />
continuum $\gamma$-ray spectrum from the ${}^{157}$Gd($n$,$\gamma$) reaction.<br />
Our model combines these two components. The results of the comparison between<br />
the observed $\gamma$-ray spectra from the reaction and the model are reported<br />
in detail.

We report on efforts to develop reliable photonuclear cross section and photon strength function data by measuring, compiling, assessing, evaluating the available data, and producing tables of Giant Dipole Resonance parameters and global models for use in basic sciences and applications.

The neutron capture cross section of long-lived radioactive 205Pb is derived by using the nuclear reaction calculation code CCONE, based on photonuclear data. The present result is smaller than that of TENDL-2015 by a factor of 4. The derived Maxwellian averaged capture cross section (MACS) is the smallest compared to the existing data. The produced amount of 205Pb is explored with a simulated neutron flux in the Pb-Bi eutectic (LBE) target. The continuous use of the system in 25 years creates 205Pb with about 6 kg at maximum in the LBE (including natural Pb of 103 kg). The impact of the derived MACS on the stellar nucleosynthesis is investigated. It is found that the abundance of Tl is slightly enhanced due to the increase in the remaining abundance of 205Pb.

The CIELO collaboration has studied neutron cross sections on nuclides that significantly impact criticality in nuclear technologies - 235,238U, 239Pu, 56Fe, 16O and 1H - with the aim of improving the accuracy of the data and resolving previous discrepancies in our understanding. This multi-laboratory pilot project, coordinated via the OECD/NEA Working Party on Evaluation Cooperation (WPEC) Subgroup 40 with support also from the IAEA, has motivated experimental and theoretical work and led to suites of new evaluated libraries that accurately reflect measured data and also perform

The CIELO collaboration has studied neutron cross sections on nuclides that significantly impact criticality in nuclear technologies-16O, 56Fe, 235,8U and 239Pu-with the aim of improving the accuracy of the data and resolving previous discrepancies in our understanding. This multi-laboratory pilot project, coordinated via the OECD/NEA Working Party on Evaluation Cooperation (WPEC) Subgroup 40 with support also from the IAEA, has motivated experimental and theoretical work and led to suites of new evaluated libraries that accurately reflect measured data and also perform well in integral simulations of criticality.

Long-lived fission product Technetium-99 is one of the most important radioisotopes for nuclear transmutation. The reliable nuclear data are indispensable for a wide energy range up to a few MeV, in order to develop environmental load reducing technology. The statistical analyses of resolved resonances were performed by using the truncated Porter-Thomas distribution, coupled-channels optical model, nuclear level density model and Bayes' theorem on conditional probability. The total and capture cross sections were calculated by a nuclear reaction model code CCONE. The resulting cross sections have statistical consistency between the resolved and unresolved resonance regions. The evaluated capture data reproduce those recently measured at ANNRI of J-PARC/MLF above resolved resonance region up to 800 keV.

To improve accuracy of neutron nuclear data on minor actinides, a Japanese nuclear data project entitled "Research and development for Accuracy Improvement of neutron nuclear data on Minor ACtinides (AIMAC)" has been implemented. Several independent measurement techniques were developed for improving measurement precision at J-PARC/MLF/ANNRI and KURRI/LINAC facilities. Effectiveness of combining the independent techniques has been demonstrated for identifying bias effects and improving accuracy, especially in characterization of samples used for nuclear data measurements. Capture cross sections and/or total cross sections have been measured for Am-241, Am-243, Np-237, Tc-99, Gd-155, and Gd-157. Systematic nuclear data evaluation has also been performed by taking into account the identified bias effect. Highlights of the AIMAC project are outlined.

Status of the JENDL project after releasing the latest general purpose file JENDL-4.0 is described. By correcting errors and adding covariance data of JENDL-4.0, 38 files have been released as JENDL-4.0u. Development of next general purpose file JENDL-5 is also in progress. New evaluations have been performed for light nuclei, structural materials and fission products. Two special purpose files, JENDL-4.0/HE and JENDL/DDF-2015 were released in 2015. The former includes neutron induced reaction data for 130 nuclides in the energy region up to 200 MeV as well as proton induced reaction data for 133 nuclides. The latter is the decay data file of 3,237 nuclides from Z = 1 to 104 and neutron. Other two special purpose files of activation cross section and photonuclear data are under preparation and will be released soon.

In order to analyze the experimental data measured by the Accurate Neutron-Nucleus Reaction Measurement Instrument (ANNRI) at the Japan Proton Accelerator Research Complex/Materials and Life Science Experimental Facility (J-PARC/MLF), it is necessary to take into account the double-bunch structure of the neutron pulse and the energy resolution function for the operational condition of the J-PARC/MLF. The modified REFIT code has been developed to treat the double-bunch neutron pulse and the energy resolution function for J-PARC/MLF. In this study, we applied the modified REFIT code to analyze the new data of the neutron capture cross section of 155Gd and 157Gd recently measured by ANNRI in the J-PARC/MLF, and obtained the resonance parameters of two Gd isotopes. We discussed the differences between the our obtained results and the other libraries.

There is large discrepancy among the reported experimental data of the thermal neutron capture cross section of Am-241, where the activation measurements provided larger cross sections than those in the time-of-flight ones. The Westcott convention has been widely used for the derivation of the thermal neutron capture cross section in the activation measurements. We have estimated that this large discrepancy is due to the existence of the resonances below the cadmium cut-off energy (E-Cd similar to 0.5 eV). By reviewing the Westcott convention, we developed the correction method taking account of the contribution of the resonances near or below E-Cd. The correction term was evaluated using the JENDL-4.0. Application of the present method successfully improved the existing discrepancy of the thermal capture cross section of Am-241.

Neutron-nucleus cross sections calculated by macroscopic potentials are compared with a microscopic one to study the performance for long-lived fission products. The macroscopic potentials show a good agreement with the microscopic one at higher energies, where neutron experimental data are scarce. Besides it, analyses of differential elastic cross sections at low energies also suggest that the macroscopic potentials are still effective and applicable enough for the long-lived fission products.

The astrophysical origin of a rare isotope Sn-115 remains an open question. An isomer (T-1/2 = 14.1 y) in Cd-113 is an s-process branching point from which a nucleosynthesis flow reaches 115Sn. The s-process abundance of Sn-115 depends on the isomer production ratio in the Cd-112(n,gamma)Cd-113 reaction. However, the ratio has not been measured in an energy region higher than the thermal energy. We have measured gamma rays following neutron capture reactions on Cd-112 using two cluster high-purity germanium (HPGe) detectors in conjunction with a time-of-flight method at J-PARC. We have obtained the result that the relative gamma-ray intensity ratio of the isomer is almost constant in an energy region of up to 5 keV. This result suggests that the s-process contribution to the solar abundance of Sn-115 is minor. We have found that the ratio of a resonance at 737 eV is about 1.5 times higher than other ratios. This enhancement can be explained by a p-wave neutron capture. This result suggests measurements of decay gamma rays to isomers are effective to assign the spin and parity for neutron capture resonances.

The Se-77 (gamma, n) cross section was measured for the energy range from 7.6 to 13.8 MeV by using quasi-monochromatic laser-Compton scattering gamma-rays. The advanced method to deduce gamma-ray strength functions from (gamma, n) cross section was developed. By utilizing the method, the gamma-ray strength functions of Se-77,Se- 78,Se- 80 were deduced so as to reproduce the Se-77,Se- 78,Se- 80 (gamma, n) cross sections measured in this work and previous systematic measurements. The inverse (n, gamma) cross sections for Se-76,Se- 77,Se- 79 isotopes were calculated using the statistical model calculation code CCONE with the deduced gamma-ray strength functions. The uncertainty of the calculated Se-79(n, gamma)Se-80 cross section was evaluated by comparing the calculations and the experimental data on Se-76,Se- 77 (n, gamma) cross sections.

Some rare isotopes are produced by neutrino-induced reactions in supernova (SN) explosions (v-process). The isotope Nb decays to Zr with a half-life of 3.47 × 10 years. Although this isotope does not exist in the present solar system, the initial abundance ratio for Nb/ Nb at the time of solar system formation (SSF) have been measured in primitive meteorites. The astrophysical origin of Nb, however, has remained unknown. The SN v-process origin for Nb has been proposed and the SN calculation has demonstrated the v-process origin of Nb. The abundances of ν-isotopes depend on neutrino temperatures. In the calculation, the average energies of kT = 3.2, 4.0, 6.0 MeV for the electron neutrino, anti-electron neutrino, and the other neutrinos (v and v ), respectively, were used. The observed ratio of Nb/ Nb ∼ 10- can be explained by the v-process. 92 92 7 92 93 92 92 92 92 93 5 μ τ

The astrophysical origin of Sn-115 has remained still an open question. An isomer with a half-life of 14.1 y in Cd-113 is a branching point from which a nucleosynthesis flow reaches to a rare isotope Sn-115. The s-process abundance of Sn-115 depends on the ratio of the Cd-112(n,gamma)Cd-113(m) reaction cross section to the Cd-112(n,gamma)Cd-113(gs) reaction cross section. However, the isomer production ratio following the neutron capture reaction has not been measured in an energy region higher than the thermal energy. We have measured gamma-ray intensity ratios following neutron capture reactions on Cd-112 using the HPGe detectors in conjunction with a time-of-flight method at ANNRI in J-PARC.

A computer code system, CCONE, was developed for nuclear data evaluation within the JENDL project. The CCONE code system integrates various nuclear reaction models needed to describe nucleon, light charged nuclei up to alpha-particle and photon induced reactions. The code is written in the C++ programming language using an object-oriented technology.
At first, it was applied to neutron-induced reaction data on actinides, which were compiled into JENDL Actinide File 2008 and JENDL-4.0. It has been extensively used in various nuclear data evaluations for both actinide and non-actinide nuclei. The CCONE code has been upgraded to nuclear data evaluation at higher incident energies for neutron-, proton-, and photon-induced reactions. It was also used for estimating beta-delayed neutron emission.
This paper describes the CCONE code system indicating the concept and design of coding and inputs. Details of the formulation for modelings of the direct, pre-equilibrium and compound reactions are presented. Applications to the nuclear data evaluations such as neutron-induced reactions on actinides and medium-heavy nuclei, high-energy nucleon-induced reactions, photonuclear reaction and beta-delayed neutron emission are mentioned.

Neutron capture cross sections and covariances on radioactive Tc-99 and I-129 have been required for developing environmental load-reducing technology. Their evaluation was performed by using nuclear reaction calculation code CCONE and Baysian code KALMAN with data assumed on the basis of measured data. The obtained total and capture cross sections are in good agreement with the measured data. The resulting uncertainties of capture cross section were 12-18% and 20-29% for Tc-99 and I-129, respectively, in the keV energy region.

Neutron nuclear data of Xe isotopes have been evaluated in the energy region, including the resolved resonance one, from 1 keV to 20 MeV by using the theoretical nuclear reaction models. The phenomenological optical model potential was employed to calculate the total cross section for natural Xe with the coupled-channels method. The cross sections for channels of capture, (n, 2n), (n, p) and (n, ) reactions were calculated and compared with available experimental results including recently measured data. The elastic scattering angular distributions and particle emission spectra were calculated, although there is no experimental information available. Reaction cross sections of evaluated libraries were considered for comparison with the calculated results. The presently calculated cross sections reproduce better the available experimental data.

Time-of-flight spectra of the neutron capture events of Nd-142 were measured using a spallation neutron source at the Japan Proton Accelerator Research Complex. The first six resonances of Nd-142 reported in a previous work were not observed. The experimental results and cross-search of resonance energies in nuclear data libraries suggested that resonances of the impurity nuclide Pr-141 have been mistakenly assigned as Nd-142 in the previous experiment. To investigate the impact of the nonexistence of the resonances on the s-process nucleosynthesis model, the Maxwellian averaged neutron capture cross sections with and without the misassigned resonances were compared.

Improvement of accuracy of neutron nuclear data for minor actinides (MAs) and long-lived fission products (LLFPs) is required for developing innovative nuclear system transmuting these nuclei. In order to meet the requirement, the project entitled as "Research and development for Accuracy Improvement of neutron nuclear data on Minor ACtinides (AIMAC)" has been started as one of the "Innovative Nuclear Research and Development Program" in Japan at October 2013. The AIMAC project team is composed of researchers in four different fields: differential nuclear data measurement, integral nuclear data measurement, nuclear chemistry, and nuclear data evaluation. By integrating all of the forefront knowledge and techniques in these fields, the team aims at improving the accuracy of the data. The background and research plan of the AIMAC project are presented.

The neutron capture cross sections and the capture gamma-ray spectra of Ba-138 were measured in the astrophysically important energy region. Measurements were made at neutron energies from 15 to 80 keV. The neutron energy was determined by the time-of-flight method. The gamma-ray spectra showed that the primary transition pattern strongly depended on the incident neutron energy. The neutron capture cross sections were derived by the pulse height weighting technique. The present cross section values were compared with evaluated cross section data and previous measurements.

We have for the first time studied the radionuclide purity of the therapeutic isotope Cu-67 produced by the Zn-68(n, x)(67)Cu reaction. The neutrons were obtained by the C-nat(d, n) reaction using 40 MeV deuterons. We measured the gamma-ray spectra of the reaction products produced by bombarding an enriched (ZnO)-Zn-68 sample with the neutrons with a high-purity Ge detector. We found that the relative production yields of the impurity radionuclides Cu-64, Zn-65, and Zn-69m to Cu-67 are extremely low. The result indicates that the Zn-68(n, x)Cu-67 reaction is the most promising among those proposed routes until now for producing high-quality Cu-67, and could solve a longstanding problem of establishing an appropriate production method for Cu-67.

CIELO (Collaborative International Evaluated Library Organization) provides a new working paradigm to facilitate evaluated nuclear reaction data advances. It brings together experts from across the international nuclear reaction data community to identify and document discrepancies among existing evaluated data libraries, measured data, and model calculation interpretations, and aims to make progress in reconciling these discrepancies to create more accurate ENDF-formatted files. The focus will initially be on a small number of the highest-priority isotopes, namely H-1, O-16, Fe-56, U-235,U-238, and Pu-239. This paper identifies discrepancies between various evaluations of the highest priority isotopes, and was commissioned by the OECD's Nuclear Energy Agency WPEC (Working Party on International Nuclear Data Evaluation Co-operation) during a meeting held in May 2012. The evaluated data for these materials in the existing nuclear data libraries - ENDF/B-VII. 1, JEFF-3.1, JENDL-4.0, CENDL-3.1, ROSFOND, IRDFF 1.0 - are reviewed, discrepancies are identified, and some integral properties are given. The paper summarizes a program of nuclear science and computational work needed to create the new CIELO nuclear data evaluations.

Gamma-ray strength functions of Pd isotopes were investigated by using measured photonuclear reaction cross sections and neutron capture reaction data. The present results calculated by nuclear reaction calculation code CCONE well reproduce the available experimental data. It is found from the evaluation of capture gamma-ray spectra that additional resonances with a variety of strength are present at around gamma-ray energies of 5 to 6 MeV. The calculated values of s-wave gamma strength function for 106, 108 Pd are 40% smaller than compiled values derived from resolved resonance data.

After the big bang nucleosynthesis, the first heavy element enrichment in the universe was made by a supernova (SN) explosion of a population (Pop) III star (Pop III SN). The abundance ratios of elements produced from Pop III SNe are recorded in abundance patterns of extremely metal-poor (EMP) stars. The observations of the increasing number of EMP stars have made it possible to statistically constrain the explosion properties of Pop III SNe. We present Pop III SN models whose nucleosynthesis yields well reproduce, individually, the abundance patterns of 48 such metal-poor stars as [Fe/H] less than or similar to -3.5. We then derive relations between the abundance ratios of EMP stars and certain explosion properties of Pop III SNe: the higher [(C + N)/Fe] and [(C + N)/Mg] ratios correspond to the smaller ejected Fe mass and the larger compact remnant mass, respectively. Using these relations, the distributions of the abundance ratios of EMP stars are converted to those of the explosion properties of Pop III SNe. Such distributions are compared with those of the explosion properties of present day SNe: the distribution of the ejected Fe mass of Pop III SNe has the same peak as that of the present day SNe but shows an extended tail down to similar to 10(-2)-10(-5)M(circle dot), and the distribution of the mass of the compact remnant of Pop III SNe is as wide as that of the present-day, stellar-mass black holes. Our results demonstrate the importance of large samples of EMP stars obtained by ongoing and future EMP star surveys and subsequent high-dispersion spectroscopic observations in clarifying the nature of Pop III SNe in the early universe.

The neutron capture cross sections for Pb-207,Pb-208 have been measured in the neutron energy region from 10 to 110 key. The gamma-rays cascaded from a capture state to the ground state or low-lying states of Pb-208,Pb-209 were observed for the first time, using an anti-Compton NaI(Tl)) spectrometer and a TOP method. The observed discrete gamma-ray energy spectra enabled us to determine neutron capture cross sections for Pb-207,Pb-208 with small systematic errors, since we could distinguish gamma-ray of Pb-207,Pb-208(n, gamma) reactions from background gamma-ray with use of the gamma-ray spectra. The obtained cross sections include both contributions of resonance and direct capture components different from the previous TOP measurements.

The present paper aims to contribute from a neutronic aspect to activities for new cladding material development for light water reactors (LWRs) that can reduce the risk of hydrogen gas explosion. Iron (Fe), nickel (Ni), titanium (Ti), niobium (Nb) and vanadium (V) are selected as possible component elements to cover a variety of new cladding materials for LWRs. The effect of larger thermal absorption cross sections of these elements than those of zirconium (Zr), together with those of silicon carbide (SiC), on the neutron economy in LWRs is evaluated by performing pin cell burnup calculations for a conventional pressurized water reactor (PWR), a low-moderation high-burnup LWR (LM-LWR) and a high-moderation high-burnup LWR (HM-LWR). As can be anticipated from the thermal cross sections, SiC has excellent neutron economy. The materials other than SiC largely decrease discharge burnup for all three types of LWRs in comparison with Zircaloy-4. Among such elements of larger thermal absorption cross section, Nb has neutron economical advantage over the other materials except SiC in softer neutron spectrum reactors such as HM-LWR in which the atomic number ratio of hydrogen to heavy metal is 6. In conventional LWRs, stainless steel of low Ni contents has the neutron economic advantage as well as Nb for cladding material. The results of the calculations are summarized for the purpose to provide reference data for new cladding material development studies, in terms of the relation between fuel enrichment and cladding thickness from the viewpoint to achieve the same discharge burnup as the Zircaloy cladding.

The first metal enrichment in the universe was made by a supernova (SN) explosion of a population (Pop) Ill star (Pop III SN). Chemical abundance in the early universe is recorded in abundance patterns of extremely metal-poor (EMP) stars. Increasing number of the EMP stars are now being discovered and allow us to statistically constrain explosion properties of Pop Hi SNe. We present Pop Ill SN models that reproduce well individual abundance patterns of 48 most metal-poor stars with [Fe/H] less than or similar to -3.5, and derive relations between abundance ratios and explosion properties of Pop III SNe: [(C+N)/Fe] vs. an ejected Fe mass, and [(C+N)/Mg] vs. a remnant mass. Using the relations, distribution of the abundance ratios of EN P stars is converted to that of the explosion properties of Pop III SNe, which can be compared with that of the explosion properties of SNe in the present day. Large samples of :EMP stars obtained by ongoing and future EMP star surveys and subsequent high-dispersion spectroscopic observations will further clarify the nature of Pop HI SNe in the early universe.

The isotope 92Nb decays to 92Zr with a half-life of 3.47 × 107 yr. Although this isotope does not exist in the current solar system, initial abundance ratios for 92Nb/ 93Nb at the time of solar system formation have been measured in primitive meteorites. The astrophysical origin of this material, however, has remained unknown. In this Letter, we present new calculations which demonstrate a novel origin for 92Nb via neutrino-induced reactions in core-collapse supernovae (ν-process). Our calculated result shows that the observed ratio of 92Nb/93Nb ∼ 10-5 can be explained by the ν-process. © 2013. The American Astronomical Society. All rights reserved.

A new system proposed for the generation of radioisotopes with accelerator neutrons by deuterons (GRAND) is described by mainly discussing the production of Mo-99 used for nuclear medicine diagnosis. A prototype facility of this system consists of a cyclotron to produce intense accelerator neutrons from the natC(d,n) reaction with 40MeV 2mA deuteron beams, and a sublimation system to separate Tc-99m from an irradiated (MoO3)-Mo-100 sample. About 8.1 TBq/week of Mo-99 is produced by repeating irradiation on an enriched Mo-100 sample (251 g) with accelerator neutrons for two days three times. It meets about 10% of the Mo-99 demand in Japan. The characteristic feature of the system lies in its capability to reliably produce a wide variety of high-quality, carrier-free, carrier-added radioisotopes with a minimum level of radioactive waste without using uranium. The system is compact in size, and easy to operate; therefore it could be used worldwide to produce radioisotopes for medical, research, and industrial applications.

We have measured the activation cross sections producing Cu-64 and Cu-67, promising medical radioisotopes for molecular imaging and radioimmunotherapy, by bombarding a natural zinc sample with 14MeV neutrons. We estimated the production yields of Cu-64 and Cu-67 by fast neutrons from C-nat(d,n) with 40 MeV 5 mA deuterons. We used the present result together with the evaluated cross section of Zn isotopes. The calculated Cu-64 yield is 1.8 TBq (175 g Zn-64) for 12 h of irradiation; the yields of Cu-67 by Zn-67(n,p) Cu-67 and Zn-68(n,x)Cu-67 were 249 GBq (184 g Zn-67) and 287 GBq (186 g Zn-68) at the end of 2 days of irradiation, respectively. From the results, we proposed a new route to produce 67Cu with very little radionuclide impurity via the Zn-68(n,x) Cu-67 reaction, and showed the Zn-64(n,p)Cu-64 reaction to be a promising route to produce Cu-64. Both Cu-67 and Cu-64 are noted to be produced using fast neutrons.

Radiative neutron capture cross sections are of direct relevance for the synthesis of heavy elements referred to as the s-process and the r-process in nuclear astrophysics and constitute basic data in the field of nuclear engineering. The surrogate reaction technique is in active use to indirectly determine radiative neutron capture cross sections for unstable nuclei. We have devised an indirect method alternative to the surrogate reaction technique on the basis of the gamma-ray strength function (gamma SF), a nuclear statistical quantity that interconnects photoneutron emission and radiative neutron capture in the Hauser-Feshbach model calculation. We outline the gamma SF method and show applications of the method to tin, palladium, and zirconium isotopes. In the application of the gamma SF method, it is important to use gamma SF's that incorporate extra strengths of PDR and/or Ml resonance emerging around neutron threshold.

Neutron nuclear data of Tc-99 was evaluated, considering cross-sections and spectra provided from recent experiments. The evaluation was made in the incident neutron energy range from 1 keV to 20 MeV, using the optical model and nuclear reaction models. The optical model calculation based on the coupled-channels method was performed for the interaction of neutrons with Tc-99, and potential parameters appropriately chosen reasonably explain the measured data of total cross-section. The cross-section of inelastic scattering, capture, (n, 2n), (n, p), (n, a) and (n, a) reactions, and gamma-ray emission spectra were calculated on the basis of statistical model with preequilibrium and direct components, and they were compared with available experimental data. It is found that the presently evaluated cross-sections and gamma-ray emission spectra well reproduce those experimental values and that there is a large discrepancy among the present result and evaluated data for neutron emission spectra. The obtained capture cross-section increases at the energies below 1 MeV, relative to that in JENDL-4.0. This makes the transmutation efficiency of Tc-99 into stable Ru-100 by accelerator driven system enhanced. The production cross-section of Mo-99 important for the medical use of nuclear diagnostics reduces by 5-30% at the energies above 12 MeV, compared with JENDL-4.0.

For the development of JENDL-4.0, neutron nuclear data for fission product nuclides, (CS)-C-133,134,135,136,137, were revised in the incident neutron energy range from 1 eV to 20 MeV by using a coupled-channels optical model (OM), and nuclear reaction models. The OM potential parameters were determined for stable Cs-133 to reproduce the experimental data of total and elastic scattering cross sections and angular distributions of elastically scattered neutrons. The present results reasonably reproduce measured data for (n,2n), (n, p), (n, alpha), and capture reactions on Cs-133. Important differences between the present results and JENDL-3.3 are found for the capture cross sections of (CS)-C-134,137. The cross section obtained for Cs-137 was smaller than that in JENDL-3.3. This result makes the transmutation of medium-lived Cs-137 increasingly difficult. The production probabilities of metastable states for (CS)-C-134,138 via capture reactions on (CS)-C-133,137 are compared with experimental values. The present result for Cs-134m production is marginally consistent with measured data. However, a large discrepancy is recognized for Cs-138m production. The gamma-ray emission data were evaluated with available measurements, and newly compiled in JENDL-4.0. Maxwellian-averaged capture cross sections were calculated in the energy range from 1 to 10(3) keV, and are compared with other derived data.

The fourth version of the Japanese Evaluated Nuclear Data Library (JENDL-4.0) was developed with one of the aims of improving the neutron nuclear data of fission products. The isotopes of Nd, Pm, Sm, Eu, Gd, Tb and Dy of lanthanoids were newly evaluated. The resolved resonance parameters were updated and the reaction cross sections in the energy region above resolved resonances were calculated by applying a new nuclear reaction model code developed in JAEA Nuclear Data Center. The gamma-ray production data were added for all of these nuclides. The obtained cross sections are compared with available experimental data and existing evaluated libraries, and show good performance.

The fourth version of Japanese Evaluated Nuclear Data Library (JENDL-4.0) has been produced in cooperation with the Japanese Nuclear Data Committee. In the new library, much emphasis is placed on the improvements of fission product and minor actinide data. Achieving this, nuclear model codes were developed. Coupled-channel optical model parameters, which can be applied to a wide mass range, were obtained for evaluations. Thermal cross sections of many actinides were revised on the basis of experimental data or systematics. Simultaneous evaluation was performed for the fission cross sections of important uranium and plutonium isotopes above 10 keV. The new library JENDL-4.0 is made available on the Web site of the JAEA Nuclear Data Center.

The fourth version of the Japanese Evaluated Nuclear Data Library has been produced in cooperation with the Japanese Nuclear Data Committee. In the new library, much emphasis is placed on the improvements of fission product and minor actinoid data. Two nuclear model codes were developed in order to evaluate the cross sections of fission products and minor actinoids. Coupled-channel optical model parameters, which can be applied to wide mass and energy regions, were obtained for nuclear model calculations. Thermal cross sections of actinoids were carefully examined by considering experimental data or by the systematics of neighboring nuclei. Most of the fission cross sections were derived from experimental data. A simultaneous evaluation was performed for the fission cross sections of important uranium and plutonium isotopes above 10 keV. New evaluations were performed for the thirty fission-product nuclides that had not been contained in the previous library JENDL-3.3. The data for light elements and structural materials were partly reevaluated. Moreover, covariances were estimated mainly for actinoids. The new library was released as JENDL-4.0, and the data can be retrieved from the Web site of the JAEA Nuclear Data Center.

We calculate the nucleosynthesis of proton-rich isotopes in the carbon-deflagration model for Type Ia supernovae (SNe Ia). The seed abundances are obtained by calculating the s-process nucleosynthesis that is expected to occur in the repeating helium shell flashes on the carbon-oxygen (CO) white dwarf (WD) during mass accretion from a binary companion. When the deflagration wave passes through the outer layer of the COWD, p-nuclei are produced by photodisintegration reactions on s-nuclei in a region where the peak temperature ranges from 1.9 to 3.6 x 10(9) K. We confirm the sensitivity of the p-process on the initial distribution of s-nuclei. We show that the initial C/O ratio in the WD does not affect much the yield of p-nuclei. On the other hand, the abundance of Ne-22 left after s-processing has a large influence on the p-process via the 22Ne(alpha,n) reaction. We find that about 50% of p-nuclides are co-produced when normalized to their solar abundances in all adopted cases of seed distribution. Mo and Ru, which are largely underproduced in Type II supernovae (SNe II), are produced more than in SNe II although they are underproduced with respect to the yield levels of other p-nuclides. The ratios between p-nuclei and iron in the ejecta are larger than the solar ratios by a factor of 1.2. We also compare the yields of oxygen, iron, and p-nuclides in SNe Ia and SNe II and suggest that SNe Ia could make a larger contribution than SNe II to the solar system content of p-nuclei.

The astrophysical origin of a p-nucleus Sn-115 has remained still an open question. The nucleus Sn-115 may be produced by a weak branch of the s-process through a beta-unstable isomer in Cd-113. However, a neutron capture cross-section to this isomer has not been measured with high accuracy at any energy. A neutron capture cross-section for the Cd-112(n,gamma)Cd-113(m) reaction has been measured with neutrons provided from a nuclear reactor. The nucleus Sn-115 may be produced by a nucleosynthesis flow through Cd-113(m) in the s-process. We have obtained the thermal neutron capture cross-section of 0.028 +/- 0.009 [b] and the resonance integral of 1.1 +/- 0.3 [b] using a cadmium difference method. The cross-section ratio of the isomer to the ground state has been calculated as a function of the incident neutron energy, E, by using a statistical model. The calculated ratios are almost constant over a wide range of E &lt; 100 keV. We have evaluated the s-process contribution to the solar abundance of Sn-115 using the classical steady-flow model. This calculated result has shown that the production through Cd-113(m) may be minor contribution to Sn-115.

A neutron capture cross section for the Cd-112( n,gamma) Cd-113(m) reaction has been measured with neutrons provided from a nuclear reactor in order to study the astrophysical origin of a rare p-process isotope Sn-115, which may be produced by a nucleosynthesis flow through Cd-113(m) in the s-process. We have obtained the thermal neutron capture cross section of 0.028 +/- 0.009 [b] and the resonance integral of 1.1 +/- 0.3 [b] using a cadmium difference method. The cross section ratio of the isomer to the ground state has been calculated as a function of the incident neutron energy, E, by using a statistical model. The calculated ratios are almost constant over a wide range of E &lt; 100 keV. We have evaluated the s-process contribution to the solar abundance of 115Sn using the classical steady-flow model with various astrophysical parameters. This calculated result has shown that the production through Cd-113(m) may give minor contribution to Sn-115.

Y-90g radiopharmaceuticals for cancer therapy have been used together with In-111 radiopharmaceuticals for diagnostics, since a daughter nucleus of Sr-90, the ground state of Y-90, Y-90g, is a pure beta-ray emitting nucleus with no gamma-ray emissions, providing no practical way for imaging. We have noted that the 682keV isomeric state of Y-90, Y-90m, with a half-life of 3.2h as well as Y-90g can be populated significantly by Zr-90(n,p)Y-90 and Nb-93(n,alpha)Y-90 at a neutron energy of 14 MeV. On the basis of the result, we have proposed a new method to use Y-90 radiopharmaceuticals containing Y-90m for diagnostics and Y-90g for therapy, since the isomeric state decays to the ground state of Y-90 by emitting 480 and 203 keV gamma-rays, appropriate energies for imaging. Y-90 radiopharmaceuticals containing Y-90m could solve long-standing problems associated with the use of Y-90g together with In-111 for imaging.

Soft-rotator model Hamiltonian parameters were deduced for 63 even-even nuclei in the mass range 56 &lt;= A &lt;= 238 by a combination of low-lying level structure and coupled-channel proton scattering analyses toward a systematic and accurate calculation of nuclear data. It was found that the obtained effective quadrupole and octupole deformation parameters were consistent with those derived from experimental B(E2) and B(E3) data. In addition, equilibrium ground-state quadrupole deformation parameters were also in reasonable accord with theoretical results for deformed heavy nuclei. The obtained parameters often varied with neutron and/or proton numbers anomalously, showing mostly the effects of shell closure. On the other hand, some clear systematic trends were seen among major Hamiltonian parameters.

We evolve extremely metal-poor ([Fe/H] similar or equal to -3), thermally pulsing Asymptotic Giant Branch (AGB) models with the mass range of 1-8 M(circle dot). The chemical yields ejected from the models are obtained by considering mass loss. We find that the 1- and 2-M(circle dot) AGB models are not affected by hot bottom burning (HBB). Nevertheless, they produce large amount of (7)Li in an H-flash event. The occurrence of this event is associated with the ingestion of protons from the overlying H-rich envelope into the He convective shell driven by thermal pulse. The resulting (7)Li abundances in the ejecta are higher than the primordial one predicted in Big-Bang nucleosynthesis. The efficient production of (7)Li by the operation of HBB is also confirmed in the models of 4-8 M(circle dot). If these AGB stars have a low-mass companion, it is probable that mass loss from the primary AGB star brings the materials enriched in (7)Li into the secondary star. This makes the surface composition of the secondary Li-rich. The formation of Li-rich stars, however, is strongly dependent on the mass loss history and binary separation. The nucleosynthesis for the other light nuclei is also calculated up to the end of the AGB phase. We find that the abundance patterns of the metal-poor stars CS 29528-041 and CS 29497-030 are well reproduced by yields from our AGB models.

Analyzing solar system abundances, we have found two empirical abundance scaling laws for p-and s-nuclei with the same atomic number. The first scaling law is that s/p ratios are almost constant over a wide range of atomic numbers where the p-nuclei are lighter than the s-nuclei by 2 or 4 neutrons. The second law is that p/p ratios are almost constant where the second p-nuclei are lighter than the first p-nuclei by 2 neutrons. These scalings provide evidence that most p-nuclei are dominantly synthesized by the gamma-process in supernova explosions. These scalings lead to a novel concept of the "universality of the gamma-process,'' in that the s/p and p/p ratios of nuclei produced by individual gamma-processes are almost constant. We have calculated the ratios produced by the gamma-process based on core-collapse supernova explosion models under various astrophysical conditions, and found that the scalings hold for materials produced by individual gamma-processes independent of the astrophysical conditions assumed. The universality originates from three mechanisms: the shifting of the gamma-process layers in order to keep their peak temperature, the weak s-process in presupernovae, and the independence of the s/p ratios from nuclear reactions. The results further suggest an extended universality, that the s/p ratios in the gamma-process layers are not only constant but also centered on a specific value of 3. With this specific value and the first scaling law, we estimate that the ratio of s-process abundance contributions from AGB stars to massive stars will be almost 6.7 for the s-nuclei of A &gt; 90. We find that large enhancements of the s/p ratios for Ce, Er, and W are evidence that the weak s-process actually occurred before supernovae.

Analyzing the solar system abundances, we have found two empirical abundance scaling laws concerning the p- and s-nuclei with the same atomic number. They are evidence that the 27 p-nuclei are synthesized by the supernova gamma-process. The scalings lead to a novel concept of "universality of gamma-process" that the s/p and p/p ratios of nuclei produced by individual gamma-processes are almost constant, respectively. We have calculated the ratios of materials produced by the gamma-process based on core-collapse supernova explosion models under various astrophysical conditions and found that the scalings hold for individual gamma-processes independent of the conditions assumed. The results farther suggest an extended universality that the s/p ratios in the gamma-process layers are not only constant but also centered on a specific value of 3. With this specific value and the scaling of the s/p ratios, we estimate that the ratios of the s-process abundance contributions from the AGB stars to the massive stars are almost 6.7 for the s-nuclei of A &gt; 90 in the solar system.

The solar abundances show empirical scaling laws for p- and s-nuclei with the same atomic number, which are a piece of evidence that most p-nuclei are dominantly synthesized by supernova gamma-process. The scalings led to a novel concept of the universality of the gamma-process that scalings should hold for individual supernova nucleosyntheses. Supernova gamma-process calculations under various astrophysical conditions show the universality originated from three mechanism, shift of gamma-process layers, change of abundance distribution by weak s-process, independence of nuclear reaction flows. Scaling show some deviations which may originate from contribution of other nucleosynthesis processes. The corrected abundance ratios show clear correlation, which means that the scaling is robust.

General- and special-purpose JENDL data files are being produced in cooperation with the Japanese Nuclear Data Committee. Nuclear model codes have been developed in order to raise the reliability of the fourth version of JENDL General-Purpose File (JENDL-4). MA and FP data have been evaluated for JENDL-4. The capture cross section of U-235 was examined in the energy region from 2 keV to 1 MeV. As a follow-up action on the previous library JENDL-3.3, covariances of several nuclei were estimated for a study on ADS. The evaluation for the 2007 versions of JENDL High Energy File (JENDL/HE) and JENDL Photonuclear Data File (JENDL/PD), which are regarded as special-purpose files, is in the final stage. Analyses of neutron transmission experiments reveal the reliability of JENDL/HE.

The evolution of extremely metal-poor (EMP) Stars of low-/intermediate-masses is distinct from those of metal-rich stars in that the convection driven by the helium shell flash can extend outward into the hydrogen-rich layer during TP-AGB phase. In the circumstance of [Fe/H] &lt; -2.5, protons are mixed and converted into neutrons in the convective zone to promote nucleosynthesis through neutron and a-captures. We study the nucleosynthesis in the helium-flash convective zone, induced by this hydrogen mixing. In the dearth of the pristine metals, the neutron-recycling reactions, C-12(n, gamma)C-13(alpha, n)O-16, and in some cases, the subsequent O-16(n, gamma)O-17(alpha, n)Ne-20, play an important role and catalyze the syntheses of O through Mg and still heavier elements. In particular, it is demonstrated that such peculiar abundance patterns of light elements from C through Al and heavy elements of Sr as observed from the two most iron-deficient stars, HE0107-5240 and HE1327-2326, can well be reproduced in terms of the nucleosynthesis in the metal-free and EMP AGB stars. In addition, the lack of Na and Al enhancement for a carbon-rich giant HE0557-4840 can be interpreted as the absence of neutron-capture reactions because of the negligible amount of proton ingestion. Based on these results, we assign their origin to the Pop III stars, born out of the primordial gas. We also discuss about the surface pollution both via the mass transfer in the binary systems and via the accretion of interstellar gas.

We investigate hydrodynamical and nucleosynthctic properties of the jet-induced explosion of a population III 40M(circle dot) star with a two-dimensional special relativistic hydrodynamical code and compare the abundance patterns of the yields with those of the metal-poor stars. We conclude that (1) the ejection of Fe-peak products and the fallback of unprocessed materials can account for the abundance patterns of the extremely metal-poor (EMP) stars and that (2) the jet-induced explosion with different energy deposition rates can explain the difference of the abundance patterns of the metal-poor stars. Furthermore, the abundance distribution after the explosion and the angular dependence of the yield are obtained for the models with high and low energy deposition rates E-dep = 120 x 10(51)erg s(-1) and 1.5 x 10(51)erg s(-1). We also find that the peculiar abundance pattern of a Si-deficient metal-poor star HE 1424-0241 can be reproduced by the angle-delimited yield for theta = 30 degrees - 35 degrees of the model with the energy deposition rate of E-dep = 120 x 10(51) erg s(-1).

We evolve thermally pulsing AGB star models in the mass range of 1 - 8 M-circle dot. The metallicity of the models is assumed to be [Fe/H] similar or equal to -3. Mass loss is taken into account to investigate the abundance patterns of the yields ejected from the AGB models. In the 1 and 2 M-circle dot AGB models hot bottom burning (HBB) does not take place at the base of the convective envelope during interpulse phases, but the low-mass models produce Li-7 in an H-flash event. The occurrence of this event is associated with the ingestion of protons from the overlying H-rich envelope into the He-flash driven convective shell during thermal pulse phase. The resulting Li-7 abundances are higher than the primordial one based on the analysis of the WMAP data. The present investigation also confirms the efficient production of Li-7 by the HBB in the intermediate-mass (4 - 8 M-circle dot) AGB stars. If these AGB stars belong to a binary system with a low-mass companion, mass loss from the primary AGB star transfers the materials enriched in Li-7 to the surface of the secondary star and makes the surface composition Li-rich. The formation of the Li-rich stars, however, strongly depends on the mass loss history and binary separation. The nucleosynthesis of the other light elements up to the phosphorus is also followed until the end of the AGB phase. We find that the yields of the low metallicity AGB stars well reproduce the abundance patterns of extremely metal-poor stars.

The first stars in our Universe (Population II) are the useful probes for the star formation history in the very early Universe. These stars were born in the primordial gas cloud produced soon after the Big Bang and considered to be metal-free, i.e., comletely lack of elements heavier than lithium. In order to identify these survivors, we should consider the effect of changing surface abundances during their long lives. The surface abundances are modified by the accretion of gas from the interstellar matter and/or the binary mass transfer. The former possibly affects the iron group elements through the pollution of the parent cloud with the ejecta of supernovae. On the other hand, the latter can affect the abundance pattern of light and s-process elements through the evolution of primary star that experienced the internal mixing and dredge-up during thermally pulsating AGB before the final mass loss. The top three of the iron deficient stars HE1327-2326, HE0107-5240, and HE0557-4840 are reported as the candidates of the first stars by the current observations of extremely metal-poor stars in the Galactic halo. These stars have [Fe/H] &lt; -4.5 and share the common feature of large enhancement of C. We argue that these abundance patterns are testified to the evolutionary characteristics of the first stars with low- and intermediate-mass by trying to constrain the mass of primary under the assumption that they were the suvivors of secondary stars in the binary system when they were born. We also argue that the binary scenario for these stars are validated with the merging history of the Galaxy. The considerations of stellar evolution, nucleosynthesis, and Galactic chemical evolution reveal that these three stars am promising candidate for the first stars.

The first metal enrichment in the universe was made by supernova (SN) explosions of population (Pop) III stars. The history of chemical evolution is recorded in abundance patterns of extremely metal-poor (EMP) stars. We investigate the properties of nucleosynthesis in Pop III SNe by comparing their yields With the abundance patterns of the EMP stars. We focus on (1) jet-induced SNe with various properties of the jets, especially energy deposition rates [(E) over dot(dep) = (0.3 - 1500) x 10(51) ergs s(-1)], and (2) SNe of stars with various main-sequence masses (M-ms = 13 - 50M(circle dot)) and explosion energies [E = (1 - 40) x 10(51) ergs]. The varieties of Pop III SNe call explain the observations of the EMP stars: (1) higher [C/Fe] for lower [Fe/H] and (2) trends of abundance ratios [X/Fe] against [Fe/H].

evaluation of neutron-induced nuclear data for five stable isotopes of zinc (mass numbers A = 64, 66, 67, 68, and 70) was consistently carried out in the incident neutron energy range from 10(-5) eV up to 20 MeV. In the low energy region up to about 100 keV, the resonance parameters were evaluated by taking account of the available measured data. In the fast neutron region, the comprehensive calculations with nuclear reaction models, in which compound, preequilibrium, and direct processes are taken into account, were performed to estimate cross sections for various reactions and double differential cross sections of emitted neutrons and gamma-rays. The comparisons of the evaluated cross sections with the experimental data measurements. and existing evaluated nuclear data libraries are made and show a good agreement with the measurements.

detailed elemental abundance analysis has been carried out for the very metal-poor (Fe/H = -2.7)star BS 16934-002, which was identified in our previous work as a star exhibiting large overabundances of Mg and Sc. A comparison of the abundance pattern of this star with that of the well-studied metal-poor star HD 122563 indicates excesses of O, Na, Mg, Al, and Sc in BS 16934 002. Of particular interest, no excess of C or N is found in this object, in contrast to CS 22949-037 and CS 29498-043, two previously known carbon-rich, extremely metal-poor stars with excesses of the alpha-elements. No established nucleosynthesis model exists that explains the observed abundance pattern of BS 16934-002. A supernova model, including mixing and fallback and assuming severe mass loss before explosion, is discussed as a candidate progenitor of BS 16934-002.

Long-duration gamma-ray bursts (GRBs) are thought to be connected to luminous and energetic supernovae (SNe) called hypernovae (HNe), resulting from the black hole (BH)-forming collapse of massive stars. For recent nearby GRBs 060505 and 060614, however, the expected SNe have not been detected. The upper limits to the SN brightness are about 100 times fainter than GRB-associated HNe (GRB-HNe), corresponding to the upper limits to the ejected Ni-56 masses of M(Ni-56) similar to 10(-3) M. SNe with a small amount of Ni ejection are observed as faint Type II SNe. HNe and faint SNe are thought to be responsible for the formation of extremely metal-poor (EMP) stars. In this Letter, a relativistic jet-induced BH-forming explosion of the 40 M. star is investigated M, and hydrodynamic and nucleosynthetic models are presented. These models can explain both GRB-HNe and GRBs without bright SNe in a unified manner. Their connection to EMP stars is also discussed. We suggest that GRBs without bright SNe are likely to synthesize M(Ni-56) similar to 10(-4) to 10(-3) M. or similar to 10(-6) M..

Europium isotopic composition could be a good probe to investigate the neutron capture process in Asymptotic Giant Branch stars (AGB stars) and/or supernovae, because the Sm-151 and Sm-153 branchings are sensitive to the neutron densities and temperature. Here, we report Eu isotopic analyses of single SiC grains from primitive meteorites using the sensitive high resolution ion microprobe (SHRIMP). The results are compared with Eu isotopic ratios predicted from the recently determined Sm-151(n,gamma) cross-sections and the thermally pulsed s-process model of AGB stars. The observed Eu isotopic composition of SiC grains place constraints on s-process conditions such as the temperature and neutron densities in AGB stars. (c) 2006 Elsevier B.V. All rights reserved.

Using core-collapse supernova explosion models, we investigate the principle of the universality of the gamma-process, according to which the s/p abundance ratios produced by individual nucleosynthesis episode are almost constant over a wide range of atomic number. The universality originates from the shift of the gamma-process layers, the independence of the s/p abundance ratios of the nuclear reactions, and the weak s-process in presupernovae. Our calculations further suggest an extended universality in which the s/ p ratios in the gamma-process layers are not only constant but also centered around a specific value of 3. To verify this, we propose an astronomical observation of indium isotopic abundance fractions.

We report on detailed spectroscopic studies performed for the secondary star in the black hole binary (micro-quasar) V4641 Sgr in order to examine its surface chemical composition and to see if its surface shows any signature of pollution by ejecta from a supernova explosion. High-resolution spectra of V4641 Sgr observed in the quiescent state in the blue-visual region are compared with those of the two bright well-studied B9 stars (14 Cyg and v Cap) observed with the same instrument. The effective temperature of V4641 Sgr (10500 +/- 200K) is estimated from the strengths of HeI lines, while its rotational velocity, vsini (95 +/- Okms(-1)), is estimated from the profile of the Mg +/- line at 4481 A. We obtain abundances of 10 elements and find definite over-abundances of N (by 0.8 dex or more) and Na (by 0.8 dex) in V4641 Sgr. From line-by-line comparisons of eight other elements (C, O, Mg, Al, Si, Ti, Cr, and Fe) between V4641 Sgr and the,two reference stars, we conclude that there is no apparent difference in the abundances of these elements between V4641 Sgr and the two normal late B-type stars, which have been reported to have solar abundances. An evolutionary model of a massive close binary system has been constructed to explain the abundances observed in V4641 Sgr. The model suggests that the progenitor of the black hole forming supernova was as massive as similar to 35 M-circle dot on the main-sequence and, after becoming a similar to 10 M circle dot He star, underwent a "dark" explosion which ejected only N- and Na-rich outer layer of the He star without radioactive Ni-56.

Analyzing the Solar System abundance, we have found two universal scaling laws concerning the p- and s-nuclei with the same atomic number. They are evidence of the p-nucleus origin that has been discussed for long years. The first scaling is the correlation of the isotope abundances between a p-nucleus and an s-nucleus that is two neutron heavier than the p-nucleus. The abundance ratios of the s-nucleus to the p-nucleus are almost constant in a wide range of atomic numbers. This scaling indicates that the p-nucleus is dominantly produced from the s-nucleus by (gamma, n) reactions in huge photon bath in supernova explosions. The second scaling indicates that the isotope abundance ratio between two p-nuclei with the same atomic number is almost unity. These two scalings are a new useful method to verify nucleosynthesis models for the p-process. We have calculated these ratios by a p-process nucleosynthesis based on a typical core-collapse supernova explosion model. The results are consistent with the scaling in the solar abundances. In addition, the scalings provide new concepts: a universality of the p-process, a rate meter for the s-process and a new nuclear cosmochronometer.

The discoveries of two extremely iron-poor stars with [Fe/H]&lt;-5, HE0107-5240 and HE1327-2326 provided the great opportunities of verifying whether these stars are the survivors of the first generation stars; the very weak lines of detected metals in their atmospheres can be extrinsic source that is the accretion from interstellar gas or from binary companion, rather than intrinsic one. In this work, we explore the possibility that these stars were born in binary systems from the primordial clouds by considering the results of stellar evolution and nucleosynthesis in metal-free models of low to intermediate mass AGB stars. Observed abundance patterns for these 2 stars are in agreement with the results and can be explained by the binary scenario that observed stars disguise their surface abundances by the mass transfer in the binary system. In particular, we first demonstrated the reproduction of Sr without large enhancement of Ba through the neutron capture reactions in the helium flash convective region of AGB models without any iron seeds for s-process. The apparent lack of stars in -5 &lt; [Fe/H] &lt; -4 may suggest the effect of dilution by the surface convection at the red giant branch. If this is true, other Pop.III survivors can be discovered at the main sequence having [Fe/H] similar to -3, whose surface abundances are changed by the mass transfer from evolved companions in binary systems.

The solar abundances provide a concept of universality that the abundance ratios of the p-nucleus to the s-nucleus with the same atomic number are almost constant with the wide region for materials produced by individual stellar nucleosynthesis episode. We study this universality using γ -process calculations with core-collapse supernova explosions under various conditions. The calculated results show that the γ -process under the various conditions can occur but the ratios are almost constant with the wide region independent of the conditions. The shift of γ -process layers, weak s-process and the beta; -decay after the γ -process contribute to the manifestation of the universality. © Copyright owned by the author(s).

We report Eu isotopic analyses of single SiC grains from primitive meteorites using the Sensitive High Resolution Ion Microprobe. The results are compared with Eu isotopic ratios predicted from the recently determined Sm-151(n, gamma) cross sections and the thermally pulsed s-process model of AGB stars. The observed Eu isotopic compositions of SiC grains place constraints on s-process conditions such as the temperature and neutron densities in AGB stars.

The recent discovery of a hyper metal-poor (HMP: -5 less than or similar to [Fe/H] less than or similar to -4) star have raised a challenging question if these HMP stars are first generation stars in the Universe. We argue that these HMP stars are the second generation stars being formed from gases which were chemically enriched by the first generation supernovae. The key to this solution is the very unusual abundance patterns of these HMP stars with important similarities and differences. We can reproduce these abundance features with the core-collapse "faint" supernova models which undergo extensive matter mixing and fallback during the explosion (mixing-fallback model). We also show that the abundance patterns of extremely metal-poor (EMP: -4 less than or similar to [Fe/H] less than or similar to -3) stars are well-reproduced by a 25 M-circle dot hypernova mixing-fallback model and those of very metal-poor (VMP: -3 less than or similar to [Fe/H] less than or similar to -2) stars are well-reproduced by a model integrated by Salpeter's initial mass function over 13 - 50 M-circle dot models.

We find two empirical scaling laws in the solar system, which is evidence that the most probable origin of the p-nuclei is photodisintegration reactions in supernova explosions (p-process). We also find a novel concept of "the universality of the p-process". We discuss the mechanism of this universality in typical core-collapse supernova explosion models.

Recent spectroscopic studies have revealed the presence of numerous carbon-enhanced, metal-poor stars with [Fe/H ] &lt; - 2.0 that exhibit strong enhancements of s-process elements. These stars are believed to be the result of a binary mass transfer episode from a former asymptotic giant branch (AGB) companion that underwent s-process nucleosynthesis. However, several such stars exhibit significantly lower Ba/Eu ratios than solar s-process values. This might be explained if there were an additional contribution from the r-process, thereby diluting the Ba/Eu ratio by extra production of Eu. We propose a model in which the double enhancements of r-process and s-process elements originate from a former 8-10M(circle dot) companion in a wide binary system, which may undergo s-processing during an AGB phase, followed by r-processing during its subsequent supernova explosion. The mass of Eu ( as representative of r-process elements) captured by the secondary through the wind from the supernova is estimated and is assumed to be proportional to the geometric fraction of the secondary (low-mass, main-sequence) star with respect to the primary (exploding) star. We find that the estimated mass is in good agreement with a constraint on the Eu yield per supernova event obtained from a Galactic chemical evolution study, when the initial orbital separation is taken to be tilda similar to 1 yr. If one assumes an orbital period on the order of 5 yr, the efficiency of wind pollution from the supernova must be enhanced by a factor of similar to 10. This may, in fact, be realized if the expansion velocity of the supernova's innermost ejecta, in which the r-process has taken place, is significantly slow, resulting in an enhancement of accretion efficiency by gravitational focusing.

We investigate the nucleosynthesis in the helium flash convective zone, triggered by the hydrogen mixing, for extremely metal-poor stars of low and intermediate mass. Mixed hydrogen is converted into neutron through C-12(p,gamma)N-13(e+v)C-13(alpha,n)O-16 and the doubly neutron-recycling reactions C-12(n,gamma)C-13(alpha,n)O-16(n,gamma)O-17(alpha,n)Ne-20 operate. In addition to oxygen and neon, not only light elements from sodium through phosphorus but also the s-process elements, heavier than iron, are synthesized via successive neutron captures with Ne-20 as seeds even in the stars originally devoid of metals. We follow the both the doubly neutron-recycling reactions and the s-process nucleosynthesis up to Ph and Bi by varying model parameters such as the amount of mixed C-13. The resultant abundance patterns is shown to reproduce the observed enhancement not only of oxygen, the light elements but also Sr observed from HE 0107-5240 and HE 1327-2326.

We study nucleosynthesis of p-nuclei in the carbon deflagration model for Type la supernovae (SNe Ia) by assuming that seed nuclei are produced by the s-process in accreting layers on a carbon-oxygen white dwarf during mass accretion from a binary companion. We find that about 50% of the p-nuclides are synthesized in proportion to the solar abundance and that p-isotopes of Mo and Ru which are significantly underproduced in Type II supernovae (SNe H) are produced up to a level close to other p-nuclei. Comparing the yields of iron and p-nuclei in SNe Ia we find that SNe Ia can contribute to the galactic evolution of the p-nuclei. Next, we consider nucleochronology of the solar system formation by using four radioactive nuclides and apply the result of the p-process nucleosynthesis to simple galactic chemical evolution models. We find that when assumed three phases of interstellar medium are mixed by the interdiffusion with the timescale of about 40 Myr Mn-53/Mn-55 value in the early solar system is consistent with a meteoritic value. In addition, we put constraints to a scenario that SNe Ia induce the core collapse of the molecular cloud, which leads to the formation of the solar system.

The influence of a large variation of Ye on explosive yield is investigated. We calculate nucleosynthesis with the initial electron fraction Ye ranging from 0.48 to 0.58 in explosive Si burning region in Population 111, 25 MD supernovae. We obtain the significant overproduction of odd elements, K and Sc. In the Y-e &lt; 0.5 cases light p-process nuclei are enhanced. We find that the abundance pattern taken from arbitrary mixture of each nucleosynthesis yield in various values of Ye can reasonably explain that in observed extremely metal-poor stars.

The recent discovery of a hyper-metal-poor (HMP) star, with a metalticity Fe/H smaller than 1/1000,000 of the solar ratio, together with one earlier HMP star, has raised a challenging question whether these HMP stars are the actual first-generation, tow-mass stars of the universe. We argue that these HMP stars are second-generation stars formed from gases that were chemically enriched by the first-generation supernovae. The key to this solution is the very unusual abundance patterns of these HMP stars and the similarities and differences between them. We can reproduce these abundance features with core-collapse "faint" supernova models that include extensive matter mixing and fallback during explosions.

We calculate nucleosynthesis of proton-rich isotopes in the Carbon deflagration model for Type Ia supernovae (SNe Ia). We investigate the influence of variations in the C/O ratios and Ne-22 abundance left in accreting CO white dwarf on the p-process nuelcosynthesis and the sensitivity of the seed abundance, distribution. We find that about 55% of the p-nuelides are produced at the levels that can explain the solar abundances in all adopted cases of initial compositions. Mo and Ru isotopes severely deficient in Type II supernovae (SNe II) are enhanced by a factor of similar to 10, but unavoidable underproduction still exists. We also compare the yields of Fe-56 and p-nuclei in SNe la and SNe II, and obtain a result that C-deflagration supernovae can contribute to the galactic evolution (and the solar system) of the p-nuclei if the s-process occurs in accreting CO white dwarfs at the similar efficiency as in AGB stars.

Analyzing the solar system abundances, we find two universal scaling relations concerning the p- and s-nuclei. These scalings indicate that the gamma-process nucleosynthesis in supernova, (SN) explosions is the most probable origin of the p-nuclei. In addition the scalings lead to new concepts: a universality of the gamma-process and a new nuclear cosmochronometer. Calculations of the gamma-process are carried out for typical core-collapse SN explosion models. These confirm the observed

We present results of p-process nucleosynthesis in core collapse supernova-e (SNe). We focus on the influence of different explosion energies and metallicities on p-process yields. We find that overproduction factors have a strong sensitivity on peak temperatures and that the distribution of normalized mean overproduction factors is robust to changing the explosion energy and metallicity. Our results indicate that (1) the contribution to the galactic evolution of p-nuclei from stars with Z less than or similar to Z circle dot/20 reduces significantly, and (2) more massive (M greater than or similar to 25M circle dot) and energetic SNe may be a dominant production site of the p-nuclei.

We investigate important reactions and reaction paths in order to reproduce the isotopic ratios of characteristic elements, C, N, and Si, in presolar SiC grains from novae. We find that the N-isotopic ratio strongly depends on the temperature profile in a nova explosion. By using this temperature dependence, we obtain a favorable temperature profile during a nova outburst. Moreover, the calculated Si-30/Si-28 ratio is high compared with the observational data of presolar nova grains. We also find that this overproduction of 30 Si can be avoided if the reaction rate of 3P(p, gamma)(31) S, which is experimentally still unknown, could increase by a factor of a few tens around the temperature of similar to 3 X 10(8) K.

Recent observational and theoretical advances in studies of gamma-ray bursts (GRBs) indicate that there can be a significant "dark side" to the GRB energy budget: besides the ultrarelativistic jet giving rise to the bright gamma-ray emission, there can be an even greater amount of "dark" energy contained in an accompanying, mildly relativistic outflow. The occurrence of such outflows are strongly supported in theoretical models, particularly for collapsar-type GRB progenitors, and also has been directly confirmed in observations of GRB030329/SN2003dh. This outflow component, which should be more baryon-rich than the GRB jet, can have interesting implications for nucleosynthesis. Inside the outflow, light elements may be produced through reactions similar to big bang nucleosynthesis. Heavy element synthesis by neutron capture can also take place, sometimes by a moderately rapid "n-process" rather than an r-process. The resulting nucleosynthetic products may be observationally relevant for the most metal-poor stars, as well as the companion stars of black hole binary systems.

Analyzing the solar system abundance, we find two universal scaling laws concerning the p and s nuclei. They indicate that the gamma process in supernova (SN) explosions is the most probable origin of the p nuclei that has been discussed with many possible nuclear reactions and sites in about 50 years. In addition, the scalings lead to new concepts: a universality of the gamma process and a new nuclear cosmochronometer. We carry out gamma-process nucleosynthesis calculations for typical core-collapse SN explosion models, and the results satisfy the observed scalings.

We have calculated models for low-mass, metal-deficient ([Fe/H] = -2.7) stars from the zero-age main sequence through the thermally. pulsing asymptotic giant branch (TP-AGB) phase. We confirm that the entropy barrier between the H-rich envelope and the He intershell can be surmounted by the energy released by thermal pulses during the early phase of the TP-AGB. For models in the mass range of 1 less than or equal to M/M-. &lt; 3, this energy release causes the top of the flash-driven convective shell to reach into the bottom of the overlying H-rich envelope. Protons are then carried downward into the hotter He- and C-12-rich layer, while He intershell material is mixed upward. This phenomenon causes the surface chemical composition to change dramatically. In particular, surface abundances are enriched in CNO elements by as much as 1 to 3 orders of magnitude. Lithium is also enhanced by this event in the 1, 1.5, and 2 M-. models. We have also studied the formation and reactions of C-13 as protons are mixed into the He intershell. We find that this mixed material experiences the s-process through the alpha-capture reaction on newly synthesized C-13 under convective conditions during the thermal pulse. This results in neutron-capture nucleosynthesis under relatively high neutron density environments. In lower mass models, the s-abundance distributions would be characterized by the small number of neutron irradiations through the standard s-process, which occurs under radiative conditions in a C-13 pocket as a result of the immediate termination of the third dredge-up. Accordingly, in extremely metal-poor stars, we may observe the s-element distributions mainly created by the s-processing relevant to the proton-mixing event. Furthermore, we discuss possible observational signatures of the mixing of protons into He-burning regions.

Gamma-ray bursts (GRBs) must originate from low baryon load, ultrarelativistic outflows; however, slower, more baryon-rich outflows (BROs) should also arise in connection with GRBs as "circum-jet winds" and/or "failed GRBs". We study the possibility of nucleosynthesis within such BROs by conducting detailed reaction network calculations in the framework of the fireball model, showing that they can be interesting sites for synthesis of heavy neutron capture elements, as well as of light elements such as deuterium. These products may be observable in the companion stars of black hole binary systems or in extremely metal-poor stars, offering an interesting probe of conditions in the central engine.

Robust generation of gamma-ray bursts (GRBs) implies the formation of outflows with very low baryon loads and highly relativistic velocities, but more baryon-rich, slower outflows are also likely to occur in most GRB central engine scenarios, either as "circumjet winds" or as "failed GRBs." Here we study the possibility of nucleosynthesis within such baryon-rich outflows by conducting detailed reaction network calculations in the framework of the basic fireball model. It is shown that high baryon load fireballs attaining mildly relativistic velocities can synthesize appreciable quantities of heavy neutron capture elements with masses up to the platinum peak and beyond. Small but interesting amounts of light elements such as deuterium and boron can also be produced. Depending on the neutron excess and baryon load, the combination of high entropy, rapid initial expansion, and gradual expansion at later times can cause the reaction flow to reach the fission regime, and its path can be intermediate between those of the r- and s-processes ("n-process"). The nucleosynthetic signature of these outflows may be observable in the companion stars of black hole binary systems and in the most metal-poor stars, potentially offering an important probe of the inner conditions of the GRB source. Contribution to the solar abundances for some heavy elements may also be possible. The prospects for further developments in various directions are discussed.

We report on the first measurement of the Eu isotope fractions (Eu-151 and Eu-153) in s-process element - enhanced metal-poor stars. We use these ratios to investigate the Sm-151 branching of s-process nucleosynthesis. The measurement was made by detailed study of Eu II lines that are significantly affected by hyperfine splitting and isotope shifts in spectra of the carbon-rich very metal poor stars LP 625 - 44 and CS 31062 - 050, observed with the Subaru Telescope High Dispersion Spectrograph. The Eu-151 fractions [fr(Eu-151) = Eu-151/(Eu-151 + Eu-153)] derived for LP 625 - 44 and CS 31062 - 050 are 0.60 and 0.55, respectively, with uncertainties of about +/- 0.05. These values are higher than found in solar system material but agree well with the predictions of recent s-process models. We derive new constraints on the temperature and neutron density during the s-process based on calculations of pulsed s-process models for the Eu-151 fraction.

The evolution of stars with masses ranging between 1 and 3M(circle dot), metallicity [Fe/H] = -2.7 and He mass fraction Y = 0.24 is followed from the zero-age main sequence through core He burning up to the thermally pulsing asymptotic giant branch phase. We find that the second. thermal pulse leads to the injection of protons into a flash-driven convective shell, the outer part of which reaches the lower part of the hydrogen tail. The energy produced by proton capture reactions then induces various changes in the stellar interior. The main results of this event are that the surface abundances of CNO and Li-7 become highly enhanced relative to solar abundance. We describe a new production mechanism for Li-7 by this phenomenon.

We have investigated evolution of low-mass, low-metallicity AGB stars. We evolved models with masses ranging from 1 to 3M(circle dot) and metallicity of [Fe/H]= -2.7. We found for M less than or similar to 2.5M(circle dot) models that in the early phase of the AGB evolution convective shell triggered by thermal runaway of He shell burning extends upwards and reaches into the bottom of the overlying H-rich envelope. Protons are mixed into hotter He intershell. Proton capture reactions occur under He burning conditions and lead to release of huge amounts of energy. This phenomenon causes the surface chemical composition to change dramatically. We present surface abundance changes of CNO elements and lithium in this event.

We have made a parametric study of s-process nucleosynthesis in the metal poor ([Fe/H] = —2.7) stars LP625-44 and LP706-7. We find that a high neutron exposure and a small overlap factor are necessary to fit the abundance pattern observed in these two metal-deficient stars, particularly the abundance ratios, Pb/Ba ≈ 1 and Ba/Sr ≈ 10. We have also constructed stellar models to better understand how such s-process conditions could arise. We have calculated a 2M ⊙ model star with metallicity [Fe/H] = —2.7 from the ZAMS up to AGB phase. We find that for such low-metallicity stars the He convective shell reaches the bottom of the overlying H-rich envelope at the second thermal pulse. Protons are then carried into the hotter He burning layers and 13C is formed as protons mix into the He shell. Subsequently, material in the H-flash driven convective zone experiences a high neutron exposure due to the 13C(α, n) reaction. This results in a new neutron-capture s-process paradigm in which the abundances are characterized by only one neutron exposure. We suggest that this new s-process site may be a significant contributor to the s-process abundances in low-metallicity ([Fe/H] ≤ —2.5) stars. © 2014 Atomic Energy Society of Japan. All Rights Reserved.

We report abundance estimates for neutron capture elements, including lead (Pb), and nucleosynthesis models for their origin, in two carbon-rich, very metal-poor stars, LP 625-44 and LP 706-7. These stars are subgiants whose surface abundances are likely to have been strongly affected by mass transfer from companion asymptotic giant branch (AGB) stars that have since evolved to white dwarfs. The detections of Pb, which forms the final abundance peak of the s-process, enable a comparison of the abundance patterns from Sr (Z=38) to Pb (Z=82) with predictions of AGB models. The derived chemical compositions provide strong constraints on the AGB stellar models, as well as on s-process nucleosynthesis at low metallicity. The present paper reports details of the abundance analysis for 16 neutron capture elements in LP 625-44, including the effects of hyperfine splitting and isotope shifts of spectral lines for some elements. A Pb abundance is also derived for LP 706-7 by a reanalysis of a previously observed spectrum. We investigate the characteristics of the nucleosynthesis pathway that produces the abundance ratios of these objects using a parametric model of the s-process without adopting any specific stellar model. The neutron exposure tau is estimated to be about 0.7 mbarn(-1), significantly larger than that which best fits solar system material, but consistent with the values predicted by models of moderately metal-poor AGB stars. This value is strictly limited by the Pb abundance, in addition to those of Sr and Ba. We also find that the observed abundance pattern can be explained by a few recurrent neutron exposures and that the overlap of the material that is processed in two subsequent exposures is small (the overlap factor r similar to 0.1).

We explore models for s-process nucleosynthesis in the recently discovered [Fe/H]= -2.7 s-enhanced star LP625-44. We apply schematic pulsed neutron source models and show that optimum fits to the observed elemental distribution imply that either a single neutron exposure or that few multiple exposures have contributed to produce the observed abundances. These results are interpreted in the context of the Case II' third dredge-up scenario recently proposed to occur in stars with [Fe/H] less than or similar to -2.5. We argue that this star maybe the first evidence for this new s-process paradigm in low-metallicity stars.

We studied the s-process nucleosynthesis in the canonical method by using a large dimension network code. We found that (1) an appropriate neutron exposure exists to best fit the observed abundances in LP 625-44 and LP 706-7 with metallicity [Fe/H] = -2.7, and (2) in this exposure the observational discovery of Pb/Ba similar to1 and Ba/Sr similar to10 are well explained. High neutron exposure and a small overlap factor are necessary to fit the abundance pattern in these two metal-deficient stars. An equilibrium pattern, except for lead, can be obtained by a single neutron irradiation. A He convective shell developed by a thermal pulse is likely to be a viable site for the s-process in metal-deficient stars.

We have compared stellar evolution models with the three intermediate-mass binary systems V2291 Oph, alpha Aur, and eta And, whose masses are determined accurately within 7%. These systems were recently regarded by Schroder and coworkers as systems that favor evolution with moderate overshoot mixing from the convective cores. While they assumed a standard Population I metallicity for these binaries, we have taken into account the available heavy-element abundance data in the literature. We have taken two approaches for each system. First, assuming no care overshooting, we have adjusted helium abundance for each binary to obtain the best fit. Second, adopting a helium abundance from a standard metallicity-helium relation, we have estimated a required extent of core overshooting l(ov). Our results indicate that the required extent of core overshooting is less than similar to 0.15H(p), which is smaller than the extent estimated by Schroder and his collaborators. The main reason for the difference is attributed to the fact that we have taken into account published estimates of metallicity for each system. We have found that to obtain a good fit with red components we have to modify the ratio of mixing length to pressure scale height for each system. The required ratio is found to be smaller for a metal-poor system and vice versa.