Hiroaki Utsunomiya

NACRE II: an update of the NACRE compilation of charged-particle-induced thermonuclear reaction rates for nuclei with mass number A < 16

Abstract An update of the NACRE compilation [3] is presented. This new compilation, referred to as NACRE II, reports thermonuclear reaction rates for 34 charged-particle induced, two-body exoergic reactions on nuclides with mass number A 16 , of which fifteen are particle-transfer reactions and the rest radiative capture reactions. When compared with NACRE, NACRE II features in particular (1) the addition to the experimental data collected in NACRE of those reported later, preferentially in the major journals of the field by early 2013, and (2) the adoption of potential models as the primary tool for extrapolation to very low energies of astrophysical S-factors, with a systematic evaluation of uncertainties. As in NACRE, the rates are presented in tabular form for temperatures in the 10 6 ≲ T ⩽ 10 10 K range. Along with the ‘adopted’ rates, their low and high limits are provided. The new rates are available in electronic form as part of the Brussels Library (BRUSLIB) of nuclear data. The NACRE II rates also supersede the previous NACRE rates in the Nuclear Network Generator (NETGEN) for astrophysics. [ http://www.astro.ulb.ac.be/databases.html ]

Excited state production and temperature measurement in a heavy ion reaction

An effective temperature inferred from the slope of kinetic energy spectra of the emitted fragments is not reflected in the relative populations of excited states of the emitted nuclei. We found that the excited state populations of 6Li, 7Li and 7Be emitted near 90° in the lab from the reaction of 490 MeV 14N with Ag are significantly lower than those expected on the basis of their effective temperature.

Multiplicity of γ-rays following fast alpha;-particle emission in the 95 MeV 14N + 159Tb reaction

Abstract Average γ-multiplicities for the reaction 159 Tb ( 14 N , αx n ) 169−x Yb at 95 MeV have been measured as a function of E α . A remarkable linear relationship is found between the gamma;-multiplicity m γ and the angular momentum l α carried off by the fast alpha;-particles: m γ = al α + b , b

Determination of the temperatures of hot nuclei from “first chance” emission spectra

Abstract The “first chance” spectra of light charged particles and neutrons emitted from 160Yb produced in the 60Ni+100Mo reaction have been isolated. The same initial temperature for the different evaporated particles and a decrease of the Coulomb barriers for the charged particles are observed. The inverse level density parameter K= A/ a reaches a value of 13.8±0.7 MeV at ETH≈236 MeV, confirming the decrease of the parameter a at excitation energies above 150 MeV.

Limitations on linear momentum transfer in 14N induced reactions on 238U at EA=15, 20, 25 and 30MeV☆

Abstract Linear momentum transfer distributions have been dermimined for 14 N induced reactions on 238 U by measuring the folding angle between two coincident fission fragments. The data follow the systematic trends previously established for alpha conjugate projectile nuclei. Over the range of energies investigated, the most probable linear momentum transfer has not reached a limiting value. Extrapolation of the present results indicates that complete fusion should cease to be a relevant reaction mechanism above incident energies of E A =40−45 MeV

Emission of complex nuclei in 12C induced reactions at EA = 15 and 30 MeV☆

Abstract Cross sections for emission of complex nuclei (Z ≈ 3–20) with energies close to the exit channel Coulomb barrier increase by more than one order of magnitude for 12C induced reactions on Au between the incident energies of E A = 15 and 30 MeV. For reactions on Ag at E A = 30 MeV , the element yields exhibit a characteristic power law dependence. Simple statistical calculations reproduce the qualitative trends of the element yields.

Direct determination of photodisintegration cross sections and the p-process

Abstract 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.

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

Cross sections of the {sup 186}W, {sup 187}Re, {sup 188}Os({gamma},n) reactions were measured using quasimonochromatic photon beams from laser Compton scattering 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{sub {sigma}} for the neutron capture on the 9.75 keV state in {sup 187}Os. Implications of F{sub {sigma}} for the Re-Os cosmochronology are discussed with a focus on the uncertainty in the estimate of the age of the galaxy.

Preequilibrium α-particle emission in heavy-ion reactions

Abstract The α-particle emission following 14 N-induced reactions on various heavy targets at 85–115 MeV has been studied. Cross sections of heavy residual nuclei produced after α-emission were measured in the case of the 209 Bi target and were found to be close to the angle-integrated cross sections of α-particles, indicating that the α-emission mainly takes place in a binary process. The measured angular distributions of α-particles are pronouncedly forward-peaked, while the energy spectra are always characterized by the Maxwellian distribution even at forward angles and reproduced excellently by the statistical evaporation formula when nuclear temperature is treated as a free parameter. The resultant value of the temperature is high (4–6 MeV) at forward angles and decreases monotonically with increasing emission angles. The energy and angular distributions of protons, deuterons and tritons were also measured in the 181 Ta + 14 N reaction at 115 MeV. The results are similar to those of α-particles. In particular, nuclear temperatures turned out nearly equal to each other, being consistent with the hot-spot interpretation for the relevant preequilibrium light-particle emission.

A flexible 4π neutron detector for in-beam studies: the Texas A&M neutron ball

Abstract A 4π “neutron ball” is described. This detector operates on the same principles as the liquid scintillator tanks traditionally employed in low energy fission studies. However, the current device has been specifically designed for in-beam experiments. The system features a comparatively large scattering chamber and a segmented tank. The response of the detector to 252 Cf neutrons is discussed and compared to Monte Carlo simulations. Some results from in-beam studies are also presented.