Calculation of astrophysical reaction rate of 82Ge(n,γ)83Ge

The neutron capture reaction on a neutron-rich near closed-shell nucleus 82Ge may play an important role in the r-process following the fallout from nuclear statistical equilibrium in core-collapse supernovae.By carrying out a DWBA analysis for the experimental angular distribution of 82Ge(d, p)83Ge reaction we obtain the single particle spectroscopic factors, S2,5/2 and S0,1/2 for the ground and first excited states of 83Ge=82Ge(⊕)n, respectively. And then these spectroscopic factors are used to calculate the direct capture cross sections for the 82Ge(n, γ)83Ge reaction at energies of astrophysical interest. The optical potential for neutron scattering on unstable nucleus 82Ge is not known experimentally. We employed a real folding potential which was calculated by using the proper 82Ge density distribution and an effective nucleon-nucleon force DDM3Y.The neutron capture reactions on neutron-rich closed-shell nuclei are expected to be dominated by the direct capture to bound states. We will show that the direct capture rates on these nuclei are sensitive to the structure of the low-lying states.     

Configuration of the valence neutrons of 17B

The reaction cross section of ¹⁷B on ¹²C target at (43.7±2.4)MeV/u has been measured at the Radioactive Ion Beam Line in Lanzhou (RIBLL). The root-mean-square matter radius (R_rms) was deduced to be (2.92±0.10)fm, while the R_rms of the core and the valence neutron distribution are 2.28fm and 5.98fm respectively. Assuming a ``core plus 2n' structure in ¹⁷B, the mixed configuration of (2s_1/2) and (1d_5/2) of the valence neutrons is studied and the     

Calculation of prompt fission neutron spectra for 235U(n,f)

The prompt fission neutron spectra for the neutron-induced fission of ²³⁵U at E_n < 5 MeV are calculated using nuclear evaporation theory with a semi-empirical model, in which the nonconstant and constant temperatures related to the Fermi gas model are taken into account. The calculated prompt fission neutron spectra reproduce the experimental data well. For the n(thermal)+²³⁵U reaction, the average nuclear temperature of the fission fragment, and the probability distribution of the nuclear temperature, are discussed and compared with the Los Alamos model. The energy carried away by γ rays emitted from each fragment is also obtained and the results are in good agreement with the existing experimental data.     

Systematical law of (n, γ) reaction cross sections of even-even nuclei

We have derived a formula for the neutron radiative capture cross section in the framework of a statistical model approach to nuclear reactions. Based on this formula, new systematics are established between the (n, γ) reaction cross section and the energy level density of a compound nucleus or a relative neutron excess of an even-even target nucleus for neutron incident energy above the resonance region to MeV. Good agreement with experimental data suggests that this new systematical law is helpful to analyze the experimental data.     

Astrophysical S-factor of the d(p,γ)3He processby

We summarize the recent effective field theory (EFT) studies of low-energy electroweak reactions of astrophysical interest, relevant to big-bang nucleosynthesis. The zero energy astrophysical S(0) factor for the thermal proton radiative capture by deuteron is calculated with pionless EFT. The astrophysical S(0) factor is accurately determined to be S(0)=0.243 eV·b up to the leading order (LO). At zero energies, magnetic transition M₁ gives the dominant contribution. The M₁ amplitude is calculated up to the LO. A good, quantitative agreement between theoretical and experimental results is found for all observables. The demonstrations of cutoff independent calculation have also been presented.     

Astrophysical S-factor of the ~(12)C(α, γ)~(16)O reaction at solar energies

The astrophysical S-factor of the4He+12C radiative capture is calculated in the potential model at the energy range 0.1-2.0 MeV.Radiative capture12C(α,γ)16O is extremely relevant for the fate of massive stars and determines if the remnant of a supernova explosion becomes a black hole or a neutron star.Because this reaction occurs at low energies,the experimental measurements are very difficult and perhaps impossible.In this paper,radiative capture of the12C(α,γ)16O reaction at very low energies is taken as a case study.In comparison with other theoretical methods and available experimental data,good agreement is achieved for the astrophysical S-factor of this process.     

Fore-aft asymmetry of the 2H(n,γ)3H at very low energies

We have used the recent effective field theory (EFT) which is constructed from two-and three-nucleon interactions, using minimal substitution in the momentum dependence of these interactions. We present the calculations of the fore-aft asymmetry of γ-rays in the reaction ²H(n,γ)³H which are based on EFT up to next-to-next-to leading order (N²LO). The results are compared with the recently reported calculations and measurements of the fore-aft asymmetry of γ-rays from neutron-deuteron radiative capture. The calculated fore-aft asymmetry of the nd radiative capture process above deuteron breakup threshold is in good agreement with the available experimental data up to 20 MeV.     

Measurement of astrophysical S-factor for 9Be(d, α0)7Li and 9Be(d, α1)7Li* reactions at low energies

The thick-target yield of the ⁹Be(d,α0)7Li and ⁹Be(d,α1)7Li*reactions has been first directly measured over deuteron energies from 66 to 94 keV.The obtained S(Ei)ofα0 andα1 have similar trends calculated by the thin-target yield,consistent with Yan’s report within the errors.Furthermore,the parametric expression of S(E)was obtained to calculate the theoretical thick target yield,and it roughly agrees with the experimental thick target yield.     

New detector system to measure (n,γ) reaction cross section precisely in China

Based on the urgent requirement of the (n,γ) reaction cross-section in the energy range of keV~MeV, 4π gamma total absorption facility (GTAF) is being constructed at China Institute of Atomic Energy (CIAE). In this paper, firstly the review of historic experimental facilities over the world is presented, and then measurement method of GTAF is described. Finally, the structure requirement for GTAF is presented. Neutron capture reactions are the key process of nucleosynthesis in astrophysics beyond iron element. The application of such facility will improve the experimental condition for the research of (n,γ) reaction.     

Cross section of reaction 181Ta(p,nγ)181W and the influence of the spin cut-off parameter on the cross section

In this work, the program Cindy was modified to calculate the formation cross section of each energy level of residual nucleus ¹⁸¹W resulting from the reaction ¹⁸¹Ta(p,nγ)¹⁸¹W. The concerned cross sections calculated at proton energy E_p=4.5-8.5 MeV agreed well with experimental results. The influence of the spin cut-off parameter in the energy level density model on the cross section was studied. The obtained results show that the influence of spin cut-off is obvious for lower energy levels.     

Measurement and analysis of the 238U(n, 2n) reactionrate in depleted uranium/polyethylene shells

In order to check the conceptual design of the subcritical blanket in a fusion-fission hybrid reactor, a depleted uranium/polyethylene simulation device with alternate shells has been established. The measurement of the ²³⁸U(n, 2n) reaction rate was carried out using an activation technique, by measuring the 208 keVγ rays emitted from ²³⁷U. The self-absorption of depleted uranium foils with different thicknesses was experimentally corrected. The distribution of the ²³⁸U(n, 2n) reaction rate at 90° to the incident D⁺ beam was obtained, with uncertainty between 5.3% and 6.0%. The experiment was analyzed using MCNP5 code with the ENDF/BVI library, and the calculated results are all about 5% higher than the measured results.     

Determination of the stellar reaction rate for 12C（α,γ）16O： using a new expression with the reaction mechanism

The astrophysical reaction rate of 12C(α, γ)16O plays a key role in massive star evolution. However, this reaction rate and its uncertainties have not been well determined yet, especially at T9=0.2. The existing results even disagree with each other to a certain extent. In this paper, the E1, E2 and total (E1+E2) 12C(α, γ)16O reaction rates are calculated in the temperature range from T9=0.3 to 2 according to all the available cross section data. A new analytic expression of the 12 C(α, γ)16 O reaction rate is brought forward based on the reaction mechanism. In this expression, each part embodies the underlying physics of the reaction. Unlike previous works, some physical parameters are chosen from experimental results directly, instead of all the parameters obtained from fitting. These parameters in the new expression, with their 3σ fit errors, are obtained from fit to our calculated reaction rate from T9=0.3 to 2. Using the fit results, the analytic expression of 12C(α, γ)16O reaction rate is extrapolated down to T9=0.05 based on the underlying physics. The 12C(α, γ)16 O reaction rate at T9=0.2 is (8.78 ± 1.52) × 1015 cm3s-1mol-1. Some comparisons and discussions about our new 12 C(α, γ)16 O reaction rate are presented, and the contributions of the reaction rate correspond to the different part of reaction mechanism are given. The agreements of the reaction rate below T9=2 between our results and previous works indicate that our results are reliable, and they could be included in the astrophysical reaction rate network. Furthermore, we believe our method to investigate the 12C(α, γ)16O reaction rate is reasonable, and this method can also be employed to study the reaction rate of other astrophysical reactions. Finally, a new constraint of the supernovae production factor of some isotopes are illustrated according to our 12C(α, γ)16O reaction rates.     

THE CROSS-SECTION MEASUREMENTS FOR 59Co(n,p)59Fe,59Co(n,α)56Mn AND 59Co(n,2n)58Co REACTIONS

The cross sections of ⁵⁹Co(n,p)⁵⁹Fe,⁵⁹Co(n,α)⁵⁶Mn AND ⁵⁹Co(n,2n)⁵⁸Co reactions have been measured at neutron energy region of 12.8MeV—17.8MeV by activation method.The coveriance matrix of measured errors was calculated,and the comparison between the values of measured and calculated using theory model was made.The evaluated excitation functions for the three reactions are given.     

The Cross Section Measurement for the Reactions of 48,46Ti(n,p) 48,46Sc 50Ti(n,α) 47Ca and 58Ni (n,2n) 57Ni 58Ni(n,p)58m+gCo

The cross sections for the ⁵⁰Ti(n,α)⁴⁷Ca,⁴⁶Ti(n,p)⁴⁶Sc、⁴⁸Ti(n,p)⁴⁸Sc and ⁵⁸Ni(n,2n)⁵⁷Ni ⁵⁸Ni(n,p)^58m+gCo reactions have been measured by using the activation method relative to the cross sections of the ²⁷Al(n,α)²⁴Na reaction in the neutron energy range of 13.50—14.81MeV.The neutron energies were determined by the cross section ratios of the ⁹⁰Zr(n,2N) ^89m+gZr and ⁹³Nb (n,2n) ^92mNb reactions.The results obtained are compared with the published and to be published data of several authors.     

Determination of the ~(12)C(p, γ)~(13)N reaction rates fromthe ~(12)C(~7Li,~6He)~(13)N reaction

The angular distribution of the 12C(7Li,6He)13N reaction at E(7Li) = 44.0 MeV was measured at the HI-13 tandem accelerator of Beijing, China. The asymptotic normalization coefficient (ANC) of 13N → 12C + p was derived to be (1.64 ± 0.11) fm-1/2 through the distorted wave Born approximation (DWBA) analysis. The ANC was then used to deduce the astrophysical S (E) factors and reaction rates for the 12C(p,γ)13N direct capture reaction at energies of astrophysical relevance.     

Calculation of prompt fission neutron spectrum for 233U（n,f）reaction by the semi-empirical method~

The prompt fission neutron spectra for the neutron-induced fission of ²³³U for low energy neutrons (below 6 MeV) are calculated using nuclear evaporation theory with a semi-empirical method, in which the partition of the total excitation energy between the fission fragments for the n_th+²³³U fission reactions is determined by the available experimental and evaluation data. The calculated prompt fission neutron spectra agree well with the experimental data. The proportions of high-energy neutrons of prompt fission neutron spectrum versus incident neutron energies are investigated with the theoretical spectra, and the results are consistent with the systematics. The semi-empirical method could be a useful tool for the prompt evaluation of fission neutron spectra.     

The Cross Section Measurements for the 100Mo(n2n)99Mo,96Mo(n,p)96Nb and 92Mo(n,α)89m+gZr Reactions

The cross sections for ¹⁰⁰Mo(n2n)⁹⁹Mo,⁹⁶Mo(n,p)⁹⁶Nb and ⁹²Mo(n,α)^89m+gZr have been measured by using the activation method relative to the cross sections of ²⁷Al(n,α)²⁴Na in the neutron energy range 13.40—14.79MeV.The comparison between the values of measured and calculated using theory mode was made.The evaluated excition functions for the three reactions are given.     

The Cross-Section Measurements and Evaluations for 58Ni(n,p),60Ni(n,p),62Ni(n,α) and 54Fe(n,p) Reactions

Activation techniques have been used to measure the cross-section for ⁵⁸Ni(n,p),⁶⁰Ni(n,p) and ⁶²Ni(n,α) reactions in the neutron energy range 13.6—17.8MeV.The uncertainty of measured data has been aculated from 3%—7%.The covariance matrixes for measurement error are calculated.Evaluations for ⁵⁸Ni(n,p),⁶⁰Ni(n,p),⁶²Ni(n,α) and ⁵⁴Fe(n,p) crpss-section are made.     

MEASUREMENT OF ISOMERIC CROSS-SECTION RATIO IN 133Cs(n,γ) 134Cs REACTION

The isomeric absolute cross-section have been measured for the reaction ¹³³Cs (n,c) ¹³⁴ Cs at 14.8 MeV neutron energy.The results are:σ_n,γ^134mCs=1.76±0.14mb;σ_n,γ^134gCs=5.17±0.41mb;σ_n,γ^134+gCs=6.93±0.55mb.The isomeric cross-section ratio is σ^134m_Cs/σ^134gCs=0.34±0.03 The experimental results are in agreement with the values given by S.M. Qaim andcompared with the theoretical results calculated by Huizenga-Vandenbosch theory.From this, the spin cut-off paramenter σ and the number of γ-Cascades have been de-termined.     

α-decay study of 218Ac and 221Th in 40Ar+186W reaction

In this study,²¹⁸Ac and ²²¹Th nuclides were produced via the heavy-ion induced fusion evaporation reaction ⁴⁰Ar+¹⁸⁶W.Their decay properties were studied with the help of the gas-filled recoil spectrometer SHANS and a digital data acquisition system.The cross section ratio between ²²²Pa and ²¹⁸Ac was extracted experimentally,withmeasured value 0.69(9).Two new possible α decay branches to ²²¹Th are suggested.The valence neutron configurations for the daughter ²¹⁷Ra are discussed in terms of the hindrance factors.