Theoretical studies of proton capture reactions in A～25 proton-rich nuclei

The direct proton capture and resonance proton capture properties of stellar reactions 22Mg(p,γ)23Al and 26Si(p,γ)27P are studied by employing a mean-field potential obtained from the Skyrme-Hartree-Fock(SHF) model.Calculations with the SHF potential reproduce well the loosely-bound structure of the ground states as well as the widths of the resonant states in these nuclei.With the obtained potential we estimate the reaction rates of direct proton capture and resonance proton capture to nuclei 23Al and 27P....     

Cross sections for 197Au(n, γ)198Au and 115In(n, γ)116mIn in the neutron energy region 2.0–7.7 MeV

The cross sections for the reactions ¹⁹⁷Au(n, γ)¹⁹⁸Au and ¹¹⁵In(n, γ)^116mIn have been measured with the activation method in the neutron energy region 2.0–7.7 MeV. The influence of background neutrons on the results was studied in considerable detail. The main problems are caused by low-energy neutrons produced by charged-particle reactions in the target material and secondary neutrons from nonelastic reactions in the sample and surrounding materials.The measured capture cross sections are generally lower than previous results and the deviation tends to increase with increasing neutron energy. The data are also compared with calculations based on the compound-nucleus model and quite good agreement is obtained.     

Interference of isovector and isoscalar giant quadrupole resonances in Y and Pb

We present the calculations of the fore-aft asymmetry of γ-rays in fast nucleon capture reactions ⁸⁹Y(n, γ)⁹⁰Y, ²⁰⁸Pb(n, γ)²⁰⁹Pb and ²⁰⁸Pb(p, γ)²⁰⁹Bi which are based on a consistent version of the direct-semi-direct (DSD) capture model. The results are in good agreement with observed differential cross sections.     

恒星能量下核子俘获反应率的晕核效应

恒星能量下俘获截面很难直接测量。¹⁰Be（n，γ）¹¹Be俘获反应涉及到非均匀宇宙大爆炸核合成，无直接测量实验截面数据。利用转移反应¹⁰Be（d，p）¹¹Be的渐近归一化系数（ANC）方法，计算了¹⁰Be（n，γ）¹¹Be俘获反应截面和反应率。¹¹Be是中子晕核。研究表明，在恒星能量下俘获到晕态的截面和反应率显著增大。     

Proton-induced direct capture on 21Ne and 22Ne

The direct capture process in the reactions ²¹Ne(p, γ)²²Na and ²²Ne(p, γ)²³Na has been investigated at E_p = 0.3–1.6 MeV using neon gas enriched to 91 % in ²¹Ne and to 99 % in ²²Ne, respectively. The gas was recirculated in a differentially pumped gas target system of the extended-static and quasi-point supersonic jet type. For ²²Ne(p, γ)²³Na, the direct capture process has been observed to several final states in ²³Na up to E_x = 8.83 MeV excitation energy. The deduced spectroscopic factors C²S are in fair agreement with the corresponding values from stripping reactions. The capture transition into the ²³Na ground state exhibits broad structures, which resemble Ericson fluctuations. The data remove the previously reported discrepancies in C²S for the ²³Na ground state. The excitation functions for the ²¹Ne(p, γ)²²Na reaction are dominated by broad and intense resonances, which hampered the measurement of the direct capture process. The nuclear and astrophysical aspects of the results are discussed.     

Radiative capture reactions with the participation of weakly bound light nuclei

Reactions of radiative capture of weakly bound light nuclei are investigated in the scope of the potential model. The applicability of the approach is demonstrated with an analysis of the cross section for the ⁶Li(p, ??)⁷Be reaction. Good agreement with the available experimental data is shown. The radiative capture cross section for the ⁶He(p, ??)⁷Li reaction in the region of low sub-barrier energies is evaluated. It is concluded that reactions involving ⁶He could also play a noteworthy part in stellar nucleosynthesis processes.     

Study of isotopic chain capture

Isotopic dependences of the capture cross section and the mean and mean-square angular momenta of a captured system in the ¹⁶O, ⁴⁸Ca + ^{196,200,204,208}Pb and ¹⁶O + ^152,154Sm reactions are investigated using the quantum diffusion approach. The obtained results are in good agreement with the existing experimental data.     

The role of the entrance channel in the fusion of massive nuclei

The role of the entrance channel in the fusion-fission reactions leading to nearly the same superheavy compound nucleus is studied in the framework of dynamic model. The calculations are done for ⁴⁸Ca +²⁴⁴Pu and ^74,76Ge +²⁰⁸Pb reactions which could lead to formation of superheavy element Z = 114. It is shown that for these reactions there is an energy window for the values of the bombarding energy at which a capture probability is sufficiently large. Together with the restriction coming from the intrinsic barrier for fusion, it helps to find an optimal value of the bombarding energy for a given projectile--target combination. Received: 15 July 1998     

Absolute cross section of the3He(α,γ)7Be reaction

The absolute cross section σ(E) of the³He(α, γ)⁷Be reaction has been measured fromE _c.m. =195 to 686 keV. The studies employed both a supersonic jet gas target and an extended gas target, and were carried out by the observation of the prompt capture γ-ray transitions as well as the⁷Be residual nuclei. The absolute cross sections deduced from the capture γ-rays are in good agreement with most previous work and remove a discrepancy with other earlier work. In comparison, the σ(E) values obtained from the⁷Be residual nuclei are systematically higher, suggesting a small production of additional⁷Be by contaminant reactions.     

Giant M1 resonance in the direct-semidirect model for nucleon radiative capture

The direct-semidirect model for nucleon radiative capture proceeding via giant E1 and E2 resonance states is extended to account for capture through collective M1 excitation. The ²⁰⁸Pb(N, γ₀) and ¹⁴⁰Ce(N, γ₀) reactions are investigated in the 2–10 MeV energy interval. For the M1 and isoscalar E2 neutron capture processes, calculations provide cross section values of the same order of magnitude, as well as comparable effects on γ-ray angular distributions. The model proves to be an appropriate framework for discussing the E1-M1 and E1-E2 interference processes, giving useful suggestions as to effects arising from the presence of the M1 and E2 collectivities.     

Proton direct capture on 40Ca

Excitation functions for the ⁴⁰Ca(p, γ)⁴¹Sc reaction have been measured at 0° and 90° in the proton energy range E_p = 2.1–3.1 MeV. The experimental results have been interpreted in terms of the direct capture process to the first excited state of ⁴¹Sc. The direct capture transition to the ground state has been observed only at a few proton energies. The spectroscopic factor of the first excited state in ⁴¹Sc has been found to be 1.0 ± 0.3. The direct capture cross section to the ground state is consistent with the spectroscopic factor reported from stripping reactions.     

Asymptotic normalization coefficients and astrophysical direct capture rates

Peripheral transfer reactions can be used to determine asymptotic normalization coefficients (ANCs). These coefficients, which specify the normalization of the tail of the nuclear overlap function, determine S-factors for direct capture reactions at astrophysical energies. A variety of proton transfer reactions involving both stable and radioactive beams have been used to measure ANCs. Tests have demonstrated that ANCs determined from proton transfer reactions can be used to calculate astrophysical direct capture rates to within 9%. The ¹⁰B(⁷Be, ⁸B)⁹Be and ¹⁴N(⁷Be, ⁸B)¹³C reactions have been used to measure the ANC appropriate for determining the ⁷Be(p,γ)⁸B rate, and the ¹⁴N(¹¹C, ¹²N)¹³C reaction has been used to measure the ANC required to calculate the ¹¹C(p,γ)¹²N rate. Received: 1 May 2001 / Accepted: 4 December 2001     

Tensor Force Manifestations in ab Initio Study of the 2H(d, γ)4He, 2H(d, p)3H, and 2H(d, n)3He Reactions

The ²H(d, γ)⁴He capture reaction and the ²H(d, p)³H and ²H(d, n)³He transfer reactions at very low energies are studied in an extended microscopic cluster model with a realistic nucleon–nucleon force. Our results show that the tensor force in realistic interactions plays an essential and indispensable role to reproduce the very low-energy astrophysical S factor of these reactions.     

Cross sections and rates of the thermonuclear reactions 64Zn(p,γ)65Ga and 66Zn(p,γ)67Ga

The excitation functions for the reactions of radiative proton capture, ⁶⁴Zn(p,γ)⁶⁵Ga and ⁶⁶Zn(p,γ)⁶⁷Ga, which are of interest for stellar nucleosynthesis, have been measured in the range of incidentproton energies from 1 to 2.8 MeV. The astrophysical S factor and reaction rates have been derived from the reaction cross sections. The experimental results are compared with the predictions of the Hauser-Feshbach statistical theory.     

Three-cluster model of radiative capture reactions in seven-nucleon systems. Effects of cluster polarization

We apply the microscopic three-cluster model, developed by the authors recently, to study the effects of cluster polarization on the capture reactions ³He(??, ??)⁷Be, ³H(??, ??)⁷Li, ⁶Li(p, ??)⁷Be, and ⁶Li(n, ??)⁷Li. These reactions are of great importance for astrophysical applications. Thus, the main attention is paid to the cross sections (or the astrophysical S factor) of the reactions in the low-energy region. Correlations between the astrophysical S factor of the reactions at zero energy and different quantities associated with the ground state of a compound nucleus are studied in detail.     

A study of hypernucleus production by K− capture at rest

The probabilities of hypernucleus formation by K⁻ capture at rest are calculated in the bound state approximation for a wide range of target nuclei, i.e. ⁴He, ¹²C, ¹⁶O, ⁴⁰Ca, ⁹⁰Zr and ²⁰⁸Pb. The mass number dependence of the formation probabilities, the relative populations of the various states in the same nucleus and the effects of kaon- and pion-optical potentials are studied in detail. K⁻ capture at rest seems less selective in populating hypernucleus states than other reactions such as (K, π^∓) in flight and (π^±, K⁺).     

The19F(n, γ)20F reaction

The gamma-ray spectrum emitted following thermal neutron capture in¹⁹F has been studied with curved crystal and Ge(Li) spectrometers. From the 109 transitions assigned to²⁰F, 85 have been placed in a level scheme containing 26 levels. An average gammaray multiplicity of 2.8 gammas per neutron capture was observed. The neutron binding energy was found to be 6601.33(14) keV. The experimental level scheme is compared to rotational model predictions. In addition it is shown that the decay of the capture state is non-statistical and that there is a strong correlation between the strengths of excitation of levels by the (n, γ) and (d, p) reactions. Calculations of the partial cross-sections using the direct capture theory of Lane and Lynn give order of magnitude agreement with experiment.     

Bulk viscosity of a reactive (νenpe−) system

The bulk viscosity arising from neutrino absorption by neutrons, and electron capture by protons, is calculated for arbitrary degeneracy of the leptons. These reactions are the primary processes determining the bulk viscosity of collapsing stellar cores. In this context the value found is of the order of 10²⁴ g cm^?1s^?1.