Direct determination of photodisintegration cross sections and the p-process

Photon-induced reactions play a key role in the nucleosynthesis of heavy neutron-deficient nuclei, the so-called p-nuclei. In this paper we review the present status of experiments on photon-induced reactions at energies of astrophysical importance and their relevance to p-process modeling.Comment: Nucl. Phys. A, in pres

DIRECT NUMERICAL SIMULATION OF FLUIDIZED BED WITH IMMERSED BOUNDARY METHOD

The applicability of the immersed boundary (IB) method, which is one of direct numerical simulations (DNS) for multiphase flow analyses, has been examined to simulate a fluidized bed. The volumetric-force type IB method developed by Kajishima et al. (2001) has been applied in the present work. While particle-fluid interaction force is calculated with the surface integral of fluid stress at the interface between particle and fluid in the standard IB method, the volume integral of interaction force is used in the volumetric-force type IB method. In order to validate the present simulation code, drag force and lift force firstly were calculated with IB method. Then calculated drag coefficients were compared with values estimated with Schiller-Nauman and Ergun equations, while calculated lift coefficients were compared with the previous simulated results. The difference of drag was within approximately 1% except in the range of low Reynolds number. Thus, the accuracy of the present simulation code was confirmed. Next, simulation of fluidized bed was carried out. Since DNS requires a large computer capacity, only 400 particles were used. The particle is 1.0mm in diameter and 2650kg/m3 in density. From the simulated results, concentrated upward stream lines from the bottom wall were observed in some regions. This inhomogeneous flow would be attributed to particulate structure

Photon-induced Nucleosynthesis: Current Problems and Experimental Approaches

Photon-induced reactions play a key role in the nucleosynthesis of rare neutron-deficient p-nuclei. The paper focuses on (gamma,alpha), (gamma,p), and (gamma,n) reactions which define the corresponding p-process path. The relation between stellar reaction rates and laboratory cross sections is analyzed for photon-induced reactions and their inverse capture reactions to evaluate various experimental approaches. An improved version S_C(E) of the astrophysical S-factor is suggested which is based on the Coulomb wave functions. S_C(E) avoids the apparent energy dependence which is otherwise obtained for capture reactions on heavy nuclei. It is found that a special type of synchrotron radiation available at SPring-8 that mimics stellar blackbody radiation at billions of Kelvin is a promising tool for future experiments. By using the blackbody synchrotron radiation, sufficient event rates for (gamma,alpha) and (gamma,p) reactions in the p-process path can be expected. These experiments will provide data to improve the nuclear parameters involved in the statistical model and thus reduce the uncertainties of nucleosynthesis calculations.Comment: 13 pages, 6 figures, EPJA, accepte

Quasicontinuum γ\gamma-decay of 91,92^{91,92}Zr: benchmarking indirect (n,γn,\gamma) cross section measurements for the ss-process

Nuclear level densities (NLDs) and $\gamma$-ray strength functions ($\gamma$SFs) have been extracted from particle-$\gamma$ coincidences of the $^{92}$Zr($p,p' \gamma$)$^{92}$Zr and $^{92}$Zr($p,d \gamma$)$^{91}$Zr reactions using the Oslo method. The new $^{91,92}$Zr $\gamma$SF data, combined with photonuclear cross sections, cover the whole energy range from $E_{\gamma} \approx 1.5$~MeV up to the giant dipole resonance at $E_{\gamma} \approx 17$~MeV. The wide-range $\gamma$SF data display structures at $E_{\gamma} \approx 9.5$~MeV, compatible with a superposition of the spin-flip $M1$ resonance and a pygmy $E1$ resonance. Furthermore, the $\gamma$SF shows a minimum at $E_{\gamma} \approx 2-3$~MeV and an increase at lower $\gamma$-ray energies. The experimentally constrained NLDs and $\gamma$SFs are shown to reproduce known ($n, \gamma$) and Maxwellian-averaged cross sections for $^{91,92}$Zr using the {\sf TALYS} reaction code, thus serving as a benchmark for this indirect method of estimating ($n, \gamma$) cross sections for Zr isotopes.Comment: 10 pages and 9 figure

Study of deformation texture in an AZ31 magnesium alloy rolled at wide range of rolling speed and reductions

Having the lowest density among all structural metals, magnesium has opened new horizons for developing commercial alloys with successful use in a wide variety of applications [1-2]. However, the plasticity of Mg is restricted at low temperatures because: (a) only a small number of deformation mechanisms can be activated [3-4], and (b) a preferred crystallographic orientation (texture) develops in wrought alloys, especially in flat-rolled sheets [5-7]. Therefore, manufacturing processes such as rolling and stamping should be performed at elevated temperatures [1, 8]. These barriers to the manufacturing process increase the price of magnesium wrought alloy products and limits the use of Mg to castings [9-10]. As a result, many studies have been conducted to improve formability by investigating the effect of manufacturing process. Therefore the current sheet production techniques, based on DC casting and hot rolling, are basically slow because the demand is easily met [11]. Twin roll casting followed by hot rolling appears to be processing route which can fulfil high volumes and reduced costs. The present authors succeeded in single-pass large draught rolling of various magnesium alloy sheets at low temperature (<473K) by high speed rolling [12]. Based on the data available in those works [13- 17], the sheet obtained by high-speed rolling exhibited a fine-grained microstructure (mean grain size of 2-3 μm), with good mechanical properties. For these advantages, the high speed rolling is a promising process to produce high-quality rolled magnesium alloy sheets at a low cost. For these advantages, the HSR is a promising process to produce high-quality rolled magnesium alloy sheets at a low cost. The goal of this research is thus to investigate the mechanisms responsible for the much higher rollability and the grain refinement after HSR. To do that, in this study, different rolling speeds from 15 to 1000 m/min were employed to twin rolled cast AZ31B magnesium alloy and different reductions

Astrophysical reaction rate for α(αn,γ)\alpha(\alpha n,\gamma)9^{9}Be by photodisintegration

We study the astrophysical reaction rate for the formation of $^{9}$Be through the three body reaction $\alpha(\alpha n,\gamma)$. This reaction is one of the key reactions which could bridge the mass gap at A = 8 nuclear systems to produce intermediate-to-heavy mass elements in alpha- and neutron-rich environments such as r-process nucleosynthesis in supernova explosions, s-process nucleosynthesis in asymptotic giant branch (AGB) stars, and primordial nucleosynthesis in baryon inhomogeneous cosmological models. To calculate the thermonuclear reaction rate in a wide range of temperatures, we numerically integrate the thermal average of cross sections assuming a two-steps formation through a metastable $^{8}$Be. Off-resonant and on-resonant contributions from the ground state in $^{8}$Be are taken into account. As input cross section, we adopt the latest experimental data by photodisintegration of $^{9}$Be with laser-electron photon beams, which covers all relevant resonances in $^{9}$Be. We provide the reaction rate for $\alpha(\alpha n,\gamma)^{9}$Be in the temperature range from T$_{9}$=10$^{-3}$ to T$_{9}$=10$^{1}$ both in the tabular form and in the analytical form. The calculated reaction rate is compared with the reaction rates of the CF88 and the NACRE compilations. The CF88 rate is valid at $T_{9} > 0.028$ due to lack of the off-resonant contribution. The CF88 rate differs from the present rate by a factor of two in a temperature range $T_{9} \geq 0.1$. The NACRE rate, which adopted different sources of experimental information on resonance states in $^{9}$Be, is 4--12 times larger than the present rate at $T_{9} \leq 0.028$, but is consistent with the present rate to within $\pm 20$ at $T_{9} \geq 0.1$.Comment: 32 pages (incl 6 figures), Nucl. Phys. in pres

Relation between the 16O(alpha,gamma)20Ne reaction and its reverse 20Ne(gamma,alpha)16O reaction in stars and in the laboratory

The astrophysical reaction rates of the 16O(a,g)20Ne capture reaction and its inverse 20Ne(g,a)16O photodisintegration reaction are given by the sum of several narrow resonances and a small direct capture contribution at low temperatures. Although the thermal population of low lying excited states in 16O and 20Ne is extremely small, the first excited state in 20Ne plays a non-negligible role for the photodisintegration rate. Consequences for experiments with so-called quasi-thermal photon energy distributions are discussed.Comment: 4 pages, 2 figures, Proceedings Nuclear Physics in Astrophysics-II, Debrecen, Hungary, 200

Photo-disintegration cross section measurements on 186^{186}W, 187^{187}Re and 188^{188}Os: Implications for the Re-Os cosmochronology

Cross sections of the $^{186}$W, $^{187}$Re, $^{188}$Os($\gamma,n$) reactions were measured using quasi-monochromatic photon beams from laser Compton scattering (LCS) with average energies from 7.3 to 10.9 MeV. The results are compared with the predictions of Hauser-Feshbach statistical calculations using four different sets of input parameters. In addition, the inverse neutron capture cross sections were evaluated by constraining the model parameters, especially the $E1$ strength function, on the basis of the experimental data. The present experiment helps to further constrain the correction factor $F_{\sigma}$ for the neutron capture on the 9.75 keV state in $^{187}$Os. Implications of $F_{\sigma}$ to the Re-Os cosmochronology are discussed with a focus on the uncertainty in the estimate of the age of the Galaxy.Comment: 11 page

Observations on the Mating rituals of the Anaconda

This is where the abstract of this record would appear. This is only demonstration data