Ab initio many-body calculations of the (3)H(d,n)(4)He and (3)He(d,p)(4)He fusion reactions

We apply the ab initio no-core shell model combined with the resonating-group method approach to calculate the cross sections of the (3)H(d,n)(4)He and (3)He(d,p)(4)He fusion reactions. These are important reactions for the big bang nucleosynthesis and the future of energy generation on Earth. Starting from a selected similarity-transformed chiral nucleon-nucleon interaction that accurately describes two-nucleon data, we performed many-body calculations that predict the S factor of both reactions. Virtual three-body breakup effects are obtained by including excited pseudostates of the deuteron in the calculation. Our results are in satisfactory agreement with experimental data and pave the way for microscopic investigations of polarization and electron-screening effects, of the (3)H(d,γn)(4)He bremsstrahlung and other reactions relevant to fusion research.     

Electromagnetic processes in a χEFT framework

Recently,we have derived a two–nucleon potential and consistent nuclear electromagnetic currents in chiral effective field theory with pions and nucleons as explicit degrees of freedom.The calculation of the currents has been carried out to include N 3 LO corrections,consisting of two–pion exchange and contact contributions.The latter involve unknown low-energy constants (LECs),some of which have been fixed by fitting the np Sand P-wave phase shifts up to 100 MeV lab energies.The remaining LECs entering the current operator are determined so as to reproduce the experimental deuteron and trinucleon magnetic moments,as well as the np cross section.This electromagnetic current operator is utilized to study the nd and n 3 He radiative captures at thermal neutron energies.Here we discuss our results stressing on the important role played by the LECs in reproducing the experimental data.     

(n,3He)的反应截面的系统学

本文研究了中、重质量核的14MeV中子的(n,~3He)反应截面的系统学特性,在对实验数据分析,评价的基础上,给出了系统学的经验公式,计算了一批核素的反应截面,同实验值符合较好,并讨论了可能的反应机制。 The systematic characters of (n, ~3He) reaction cross sections have been studied formedium and heavy mass nucleus at 14MeV. A set of the empirital parameters have been eatracted onthe bases of analyzing and evaluating available data. The (n,~3He) reaction cross sections of somenuclei have been calculated, and a good agreement with the experimental data have been obtained.Most possible reaction mechanisms are also discussed.     

Chiral effective field theory predictions for muon capture on deuteron and {3}He

The muon-capture reactions {2}H(μ{-},ν{μ})nn and {3}He(μ{-},ν{μ}){3}H are studied with nuclear potentials and charge-changing weak currents, derived in chiral effective field theory. The low-energy constants (LECs) c{D} and c{E}, present in the three-nucleon potential and (c{D}) axial-vector current, are constrained to reproduce the A=3 binding energies and the triton Gamow-Teller matrix element. The muon-capture rates on deuteron and {3}He are predicted to be 399±3 sec{-1} and 1494±21 sec{-1}, respectively. The spread accounts for the cutoff sensitivity, as well as uncertainties in the LECs and electroweak radiative corrections. By comparing the calculated and precisely measured rates on {3}He, a value for the induced pseudoscalar form factor is obtained in good agreement with the chiral perturbation theory prediction.     

14MeV中子(n,T)与(n,3He)反应截面的系统学研究

本文研究14MeV中子(n,T)和(n,³He)反应截面的系统学特性。在考虑奇偶效应的基础上,给出了截面的系统学公式,σ_u,q=(A^1/3+1)²aexp[β(N-Z+δ)/A]。用最小二乘法拟合得到奇偶核的经验参数对(n,T)反应,α,β分别为327.602,9.592和-24.495,-14.038。对(n,³He)反应,α,β分别为0.918和-11.340。利用这套参数计算的截面与实验值符合较好。此外,文中还讨论了反应的Ω值效应以及可能的反应机制。 关键词：     

H + reactions from 1.96 to 6.20 MeV

The differential cross sections of ²H(d, d)²H, ²H(d, ³He)n, ²H(d, p)³H and ²H(d, t)p have been measured in a gas scattering chamber at ten bombarding energies between 2.0 and 6.2 MeV with accuracies ranging from ±1.7 % to ±3.4 %. The differential cross section of ²H(d, n)³He has been measured at forward angles to an accuracy of ±2.5 % at the same energies using a time-of-flight detection system. The neutron detection efficiency was calibrated from the ²H(d, ³He)n cross sections, so the neutron production cross sections reported here do not depend on any previous neutron measurements. The ²H(d, ³He)n cross sections have been converted into ²H(d, n) ³He cross sections and Legendre polynomial fits are given for the complete angular distributions of ²H(d, n)³He.     

Low energy electromagnetic processes based on the chiral effective field theory approach

Chiral effective field theory describes the interaction of nucleons and pions in the low-energy regime of QCD.This theory offers a consistent picture of nuclear forces and nuclear current operators.We study the electromagnetic processes based on ChEFT dynamical picture and compare our predictions to results obtained in the conventional framework.In particular,we consider low energy photo-disintegration of the deuteron at different orders of the chiral expansion.We investigate a role of different ingredients in the two-nucleon current operator.For the first time calculations involve consistent contributions from long-range two-pion exchange currents which appear at next-to-leading order of the chiral expansion.We present novel results for cross sections and various polarization observables.     

The quasi-free 3He(e,e′p) reaction

The proton spectral function has experimentally been determined with the ³He(e, e′p) reaction for missing energies, 0<E_m<70MeV, and recoil momenta, 0<P_B<310 MeV/c. Experimental results are obtained for both the two-body, ³He(e, e′p)²H, and three-body breakup processes. Proton momentum density distributions, obtained in a PWIA analysis, are compared with theoretical calculations: Faddeev solutions with the RSC and Paris potentials, and variational calculations with various potentials, including those with a three-nucleon interaction term. Energy-weighted sum rule results are presented and compared with theoretical predictions. The coincidence cross sections are also compared with calculations which include the effects of final state interactions and meson exchange currents. Consistency of the results with PWIA is investigated in the framework of the Chew-Low extrapolation procedure.     

单能中子源中低能成份对活化截面测量的影响

对用单能中子源作活化截面测量时低能中子干扰的影响作了分析研究,并从测量的两种常用中子源T(d,n)⁴He和D(d,n)³He的中子源能谱中验证了这种定性分析.最后给出了两个比较典型的反应⁵⁸Ni(n,P)⁵⁸Co和⁶⁴Zn(,P)⁶⁴Cu反应的截面测量结果.     

Oppenheimer-Phillips effect and electron screening ind+ d fusion reactions

Thed(d, n) ³He andd(d,p)t fusion reactions have been studied at center-of-mass energies E=1.6 to 130 keV using intense beam currents from 30, 100, and 450 kV accelerators in combination with detectors in close and far geometry. The cross sesction ratio,R(E)=σ(d,n)/σ(d, p), approaches unity (within 2%) at low energies; thus there is no experimental evidence for the Oppenheimer-Phillips effect at subcoulomb energies. The cross sections of d(d, p)t at E≦10keV show clear evidence for electron screening effects. However, the observed cross section enhancement is significantly larger than can be accounted for from available atomic physics models.     

Dynamical aspects of photonuclear reactions below pion threshold

We study the reactions (γ,p), (γ,n), (γ,pp) and (γ,nn) below pion threshold in view of a systematic treatment of electromagnetic meson exchange currents. As a numerical example we calculate the integrated and differential cross sections for (γ,p) and (γ,n) on ⁴He.     

Absolutbestimmung der Gesamtanregungsquerschnitte der Edelgase durch Elektronenstoß

With an improved Maier-Leibnitz collision chamber absolute values of the total excitation cross sections of the rare gases were measured. The half width of energy distribution in the beam of exciting electrons was approximately 0.7 eV. The results for He and Ne are in reasonable agreement with the excitation functions given by Maier-Leibnitz, if some necessary corrections (especially with regard to contact potentials) are made. Only the cross sections obtained by us are a little smaller. Furthermore the better fine structure yielded more favourable possibilities of comparison with other measurements published so far. The error should not be greater than 30%.     

He-HF(DF，TF)碰撞体系散射截面的理论计算

运用质心变换-拟合的方法,使用Murrell-Sorbie势能函数拟合在对称性匹配微扰理论下精确计算He-HF体系的相互作用能数据,得到了He原子与同位素分子HF(DF,TF)复合物的相互作用势的解析形式. 在此基础上,完成了入射He原子能量分别为50meV,59.5meV,86meV,100meV和120meV时,He-HF(DF,TF)碰撞体系散射截面的密耦计算,获得了弹性、非弹性和总积分截面等信息,并讨论了散射截面的变化趋势及特征. 关键词： He-HF(DF TF)复合物 密耦近似 散射截面 质心偏移     

不同能量下He原子与HCl分子碰撞激发分波截面的同位素效应研究

基于Huxley势函数的拟合势,通过精确度较高的密耦近似方法计算了入射能量为50meV和150meV时,氦原子的四种同位素3He,4He,9He,10He与HCl分子碰撞体系的激发分波截面.通过分析不同能量下,各碰撞体系分波截面的差异,探讨了不同入射能量时He的同位素对He-HCl碰撞体系的分波截面的影响,总结出其分波截面随量子数和体系约化质量的变化规律.     

不同能量下He原子与HCl分子碰撞激发分波截面的同位素效应研究

基于Hux1ey势函数的拟合势,通过精确度较高的密耦近似方法计算了入射能量为50 meV和150meV时,氦原子的四种同位素3He,4He,9He,10He与HCl分子碰撞体系的激发分波截面.通过分析不同能量下,各碰撞体系分波截面的差异,探讨了不同入射能量时He的同位素对He-HCl碰撞体系的分波截面的影响,总结出其分波截面随量子数和体系约化质量的变化规律.     

Energy dependence of the optical model parameters for 3He ions scattered from 40Ca and 58Ni

The differential cross sections for the elastic scattering of ³He ions on targets of ⁴⁰Ca and ⁵⁸Ni have been measured at incident energies of 27.7, 51.4, 73.2 and 83.5 MeV. The results of optical model analyses showed that only one unique potential (J_R ≈ 330 MeV · fm³) with a surface absorptive term can provide acceptable fits to the large angle elastic scattering cross sections at 83.5 MeV. The particular geometrical set found at 83.5 MeV could not, however, give an adequate fit to the data with energy less than 40 MeV. Subsequent analyses indicated that a break in the energy dependence of the real potential is observed for the low energy data. Explicit energy dependent terms were obtained by fitting all the data simultaneously. These phenomenological potentials were also compared with the folded nucleon-nucleus potential. The influence of the α-particle channels on the elastic scattering of ³He ions at 83.5 MeV was also examined.     

The intermolecular potential energy surface of Ar · HC1

Anisotropic potential energy surfaces for Ar · HC1 are obtained by simultaneous least squares fitting to molecular beam spectra, rotational line broadening cross sections, second virial coefficients and molecular beam total differential cross sections. Several potentials are obtained which given good agreement with all these data and the sensitivity of the data to various aspects of the potential is investigated. For all potentials the equilibrium configuration is linear with the atomic arrangement Ar · H-C1. Several different ways of parameterizing the intermolecular potential are considered and it is concluded that the conventional multipole parameterization is not adequate for strongly anisotropic intermolecular potentials.     

Interaction potentials and energy transfer cross sections for collisions of metastable helium and neon I: He(23 S)+Ne

Differential cross sections have been measured for He(2³ S)+Ne at kinetic energies between 28 and 370 meV. For energies above 90meV the elastic cross sections show Stückelberg oscillations from curve crossings, which lead to the energy exchange process: He(2³ S)+Ne→He(1¹ S)+Ne(2p ⁵ 4s,3d,4p). Differential cross sections for this inelastic process could be measured above 200 meV. A fit to the data gives the potentials for He(2³ S)+Ne and, less accurately, for He+Ne^*. These results offer a simple explanation, why the exothermic pumping process of the infrared lines of the HeNe laser has a threshold of about 80 meV and a small cross section.     

Quantum calculations of rotational and NMR relaxation,depolarized Rayleigh and rotational Raman line shapes for H2(HD)−He mixtures

The two ab initio vibrotor potentials of H₂?He previously published by Meyer, Hariharan, and Kutzelnigg have been composed in one potential grid. After using this potential in close coupled scattering calculations we have subsequently obtained rotational relaxation cross sections for para- and ortho-H₂, NMR relaxation times for ortho-H₂, depolarized Rayleigh line broadening cross sections for para-, ortho-, and normal-H₂, and rotational Raman line width and shift cross sections for S₀(0), S₀(2) transitions, at temperatures between 20 and 450 K. The agreement with previous and more recent measurements has been found completely satisfying, with the exception of the rotational relaxation cross sections of para-H₂. Throughout the paper previous results derived from the multiple property fit of Shafer and Gordon have been included for comparison. The new ab initio potential is obviously better, except for the rotational relaxation cross sections. The interaction potential of HD?He transformed from the new H₂?He potential is also presented in this paper. It has been used recently in a very successful application of the Waldmann-Snider kinetic theory describing transport, relaxation, and reorientation phenomena in magnetic fields. Therefore, only the rotational relaxation cross sections, converged up to about 400 K, have been presented in this paper.     

DWBA analysis of (3He,d) reactions at 90MeV and contributions from the nuclear interior

Differential cross sections of ³He elastic scatterings and (³He, d) reactions have been measured at 90 MeV for ²⁸Si, ⁵⁴Fe, ⁵⁸Ni, ⁹⁰Zr and ¹²⁴Sn. From the optical-model analysis of the elastic scattering, both shallow ($\text{V ? 105}\text{MeV}$) and deep ($\text{V ? 150}\text{MeV}$) potentials of ³He were obtained. The shallow potentials correspond to the ones which were determined uniquely from other measurements extended to more backward angles. The (³He, d) reactions have been analyzed with the DWBA using the shallow and deep potentials for ³He. The calculations using the deep potentials reproduced the data well, but those using the shallow ones did not. The contributions from the nuclear interior were investigated through the radial cutoff in the DWBA. The calculations using the shallow potentials reproduced the data well when the radial cutoffs were introduced. The effects of the radial cutoff were very small when the deep potentials were used. It was found that a much greater reduction of the contributions from the nuclear interior was needed when the shallow potentials were used in the DWBA calculations.