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1.
The decoupled Yakubovski equation is brought into an amenable form under some approximations. As the result, the number of equations to be solved is considerably reduced from the original Yakubovski equation. The whole equation becomes very close to the equations in the conventional reaction theories. The relevance to the optical potential, DWIA and the impulse approximation are discussed. In the present theory, the persistence of the channel wavefunctions in the course of multiple scatterings is not presumed. The channel wavefunctions can collapse under two-body interactions. Nevertheless, we see that the most important process is the particle transfers between bound clusters. Once the channel wavefunction is collapsed it is very difficult to revive again as a channel wavefunction. This part may be interpreted as forming a compound system.  相似文献   

2.
《Physics Reports》1987,154(3):125-204
The formalism and results of truncated coupled channels evaluations of three-body models of deutron-induced nuclear reactions are reviewed. Emphasis is placed on breakup, elastic scattering and stripping. The relations of the coupled channels method to the Faddeev method, the adiabatic approximation and the distorted wave Born approximation are discussed extensively. Although the adiabatic approximation is seen to be excellent for the wavefunction in the elastic channel, it significantly underestimates the contributions of breakup states in stripping. Significant effects are associated with coupling to relative l = 2 breakup states.  相似文献   

3.
电子碰撞原子(e,2e)反应的复极化势   总被引:3,自引:1,他引:2       下载免费PDF全文
研究包括连续通道等非处理通道的复极化势对(e,2e)碰撞过程三重微分截面的影响,即将耦合通道光学势方法得到的复极化势附加到畸变波玻恩近似方法的畸变势中,在靶态的HF近似下,计算了Ar原子和Ne原子在非共面对称几何条件下(e,2e)反应的三重微分截面.对于较高的入射能量,在实验的误差范围内,计算结果与电子动量谱的实验数据符合较好,复极化势的影响很小;对于较低的入射能量,复极化势的作用明显增大. 关键词: 复极化势 (e;2e)反应 三重微分截面 电子动量谱  相似文献   

4.
Laser-assisted electron-atomic-hydrogen “elastic" scattering is studied in the first Born approximation. The initial and final states of projectile electron are described by the Volkov wavefunctions; the dressed state of target described by a time-dependent perturbative wavefunction in soft photon approximation. The laser modified cross-sections are calculated in two distinct geometries for laser polarization either parallel or perpendicular to the incident direction of electron. The numerical results shows that the multiphoton cross-sections oscillate by a few orders over the whole scattering angular region. The results for a parallel geometry oscillate more frequently in the intermediate angles; while the results for a perpendicular geometry oscillate more frequently in the forward and backward angles. At large scattering angles, the sum rule of Kroll and Watson is noticeably violated. The laser modification on summed total cross-section increases with field strength, but decreases with field frequency and polarization deviation from the incident direction. Received 18 October 2001 and Received in final form 26 December 2001  相似文献   

5.
Nuclear reactions between composite particles with rearrangement processes are considered. The cluster model is used in describing the structure of the nuclei. With this structure we have in the initial channel as well as in the final channel, four interacting particles. These reactions are studied as a four-body problem. The scattering amplitudes are approximated by using a separable expansion for the separable potential model. The four-body equations are reduced to integral equations in the form of exact effective two-particle Lippmann-Schwinger equations. These equations are solved by standard methods in a form suitable for numerical calculations. The present four-body treatment is applied calculating the differential cross-sections for different scattering and transfer nuclear reactions. Distorted wave Born approximation calculations are used in calculating the angular distributions. The present theoretical calculations are in good agreement with the experimental angular distributions.  相似文献   

6.
7.
It is shown that a distorted wave Born approximation theory combining the Hankel function approach for the form factor with a linear recoil correction gives satisfactory results when compared to exact finite-range with recoil calculations for a large variety of heavy-ion induced one-nucleon transfer reactions. The test cases presented involve incident projectile energies in the vicinity of the Coulomb barrier as well as energies several MeV/nucleon above the barrier, strongly absorbing optical potentials as well as recently used more transparent potentials, and transfer with large recoil corrections. The exact calculations are generally reproduced with an accuracy of the order of 10%. Computing times are a factor 2 ± 0.5 larger than typical times needed for a no-recoil calculation. The limits of the method are discussed and the importance of the tails of bound states is stressed.  相似文献   

8.
韩银录 《中国物理 C》2004,28(2):177-180
根据中子与原子核U及其同位素反应的总截面,去弹性散射截面和弹性散射角分布的实验数据,获得了入射中子能量0.1—20MeV的一组普适中子与U及其同位素反应的光学模型势参数.应用光学模型,核裂变理论,耦合道理论,扭曲波玻恩近似理论,宽度涨落修正的Hauser-Feshbach理论和预平衡反应的激子模型,计算和分析了中子与238U反应的所有截面、角分布、能谱和双微分截面.理论计算与实验数据进行了分析比较  相似文献   

9.
The elastic scattering of atoms and molecules by solid surfaces is treated in a nonperturbative way using the single particle Green's function of the scattered particles. For sufficiently short ranged interactions the elastic reflection coefficient is found to approach unity in the limit of zero energy of the incident particles. Unitarity then implies zero total reaction coefficient including the sticking coefficient. The findings of the first order distorted wave Born approximation are thus generalized. The result is not in contradiction to the experimental observation of sticking coefficients increasing with decreasing energy, since quantitative approximate calculations show that the limit is reached only at extremely low energies.  相似文献   

10.
This article is concerned with excitation, ionization and electron capture collisions between charged particles and atomic systems involving a single active electron, at impact energies which are so great that Lorentz transformations between the frames of reference of the incident and target particles must be carried out as well as relativistic dynamics employed. For excitations and ionization it is sufficiently accurate to use the relativistic generalization of the first Born approximation, but for electron capture it is necessary to carry through the analysis using a relativistic generalization of the second Born approximation. Also relativistic wave functions are employed to describe the active atomic electron.  相似文献   

11.
Alternative definitions of the Born approximation and the distorted-wave Born approximation within the framework of the configuration-space Faddeev equations are explored. The most natural definition does not correspond to the Born approximation derived from the Schrödinger equation, even though the exact T-matrices for both formalisms are equivalent. The Schrödinger form is optimal, although it is shown that the differences are numerically unimportant. The DWBA corresponding to the Faddeev equations is not channel symmetric, although numerically this is unimportant for the p-d (Coulomb) case. The place in the partial-wave series beyond which the Born approximation can be effectively substituted for the exact result is briefly investigated for p-d and n-d scattering below breakup threshold.  相似文献   

12.
Based on the new measurements of total, nonelastic, elastic cross section and elastic scattering angular distributions for n+U reactions, a set of neutron optical model potential parameters is obtained in the region of incident neutron energy from 0.1 to 20 MeV. The cross sections, angular distributions, energy spectra and double differential cross sections are calculated and analyzed by optical model, nuclear fission theory, distorted wave Born approximation theory, coupled channel theory, the unified Hauser-Feshbach theory, as well as exciton model. The results indicate that our theoretical model can reasonably analysis n+ 238U reaction data with neutron energy lower than 20 MeV.  相似文献   

13.
Some principal questions of the theory of multiparticle transfer reactions are studied in the framework of Fredholm type equations. Expressions are compared to those of the distorted wave Born or coupled reaction channel approximations.  相似文献   

14.
15.
Final-state-interaction (FSI) effects are included in the treatment of the photodisintegration of the α-particle via the K-matrix approximation. These are applied to the exact AGS-type integral equation for this process at photon energies 50–100 MeV. Direct comparison with the plane-wave (Born) approximation indicates that these effects are small, which explains the good fit to the data we found previously. The FSI in the integro-differential equation treatment of the problem in configuration space are included by means of effective nucleon-trinucleon potentials constructed via an exact inverse scattering method and by using the phase shifts obtained from the K-matrix approach to the 3 + 1 → 3 + 1 scattering. Comparison between this approach and the integral-equation approach confirms the validity of this model previously employed at low energies using experimental phase shifts. Finally we show that the photonuclear cross sections are sensitive to the details of the boundstate wave functions of the 3He and 4He as calculated exactly via the AGS equations and in the integro-differential-equation approach, which for the 4He neglects higher-order correlations. Received April 18, 1994; revised September 12, 1994; accepted for publication October 12, 1994  相似文献   

16.
The elastic scattering of deuterons in deuterium has so far only been treated in Born approximation, at rather high energies. In the present paper the authors derive integro-differential equations to deal with the scattering phenomenon at low energies of a few MeV. The mutual distortion of the two deuterons at close distance turns out to have a large influence on the angular distribution. A simple and plausible assumption has been made, concerning this distortion, and the results have been compared with experiment for two energies.  相似文献   

17.
For a three-body model Hamiltonian, the scattering eigenfunction that corresponds to an incident deuteron is expanded in terms of eigenfunctions of the neutron-proton relative Hamiltonian, as suggested by Johnson and Soper. In this expansion, breakup is represented by an integral over the continuum of neutron-proton scattering states. Only states of zero relative angular momentum are included; the validity and advantages of this approximation are discussed. The continuum is divided into five discrete channels, whose coupling to each other and to the deuteron channel is treated by solving coupled differential equations with appropriate boundary conditions. It is found necessary to use a simple WKB method to take account of the long-range coupling among breakup channels; this method introduces potential matrices W and S that describe local and derivative coupling of the channels. The reaction of breakup on the elastic channel is neglected.The properties of W and S and the breakup wavefunction are examined for the case of 22.9 MeV deuterons incident on a target of mass number A ≈ 40. The Coulomb interaction is ignored, and a local Gaussian shape is used for both the real and imaginary parts of the nucleon-nucleus optical potential.It is found that a rather broad spectrum of n-p continuum states is excited, especially for low center-of-mass angular momentum. This result weakens the justification for the Johnson-Soper adiabatic theory, which emphasizes breakup into states of low relative energy.The breakup part of the wavefunction at zero n-p separation is comparable with the elastic part, but is important only over a surprisingly short range in the center-of-mass coordinate, with the result that breakup cross sections are quite small. Nevertheless, breakup produces major modifications of (d, p) cross sections. These modifications can to some extent be simulated by the Johnson-Soper method. The breakup wavefunctions show several interesting effects in their dependence on angular momentum and radius.  相似文献   

18.
On the basis of an explicit implementation of the projection-operator method and with due regard to antisymmetrization effects, formulas are constructed for the amplitudes of elastic and inelastic nuclear reactions induced by nucleons and composite particles and for the widths with respect to the nucleonic, alpha-particle, and cluster decays of nuclei. It is shown that equations governing the behavior of elastic-scattering form factors represent generalizations of the equations of the resonating-group model and coincide, provided that ground-state correlations are taken into account, with the analogous equations in the theory of open Fermi systems. It is demonstrated that the nonretarded part of the effective potential of nucleus-nucleus interaction coincides with the Hartree-Fock potential, which has a deep attractive character in accordance with the Levinson theorem, and that the retarded part of the effective potential is determined by the fragmentation of the initial states of colliding nuclei into compound states. It is revealed that the use of different elastic-form-factor representations associated with taking into account antisymmetrization effects leads to the same results for the amplitudes of elastic and inelastic nuclear reactions. The formulas obtained here for the amplitudes of direct inelastic nuclear reactions are found to differ significantly from the corresponding formulas of the distorted-wave method in the Born approximation. Problems that are concerned with the emergence of potential optical resonances for elastic form factors and with their relation to the shell-model wave functions for a compound system are investigated. A new regime of interpolation for the amplitudes of cluster form factors from the shell to the asymptotic region of a decaying nucleus is found. Implications of this interpolation for the calculated alpha-particle and cluster widths and for understanding the nature of superfluid correlations in nuclei are analyzed.  相似文献   

19.
张立民  贾昌春  王琦  陈长进 《物理学报》2014,63(15):153401-153401
在共面双对称几何条件下,利用一阶扭曲波Born近似计算了中低能电子碰撞Ar原子(3p壳层电子)单电离的三重微分截面,并与最近的实验数据做了比较.结果表明,对于Ar原子,当入射电子能量比电离阈高40 eV以上,随着入射能量的增加,binary和recoil碰撞机理逐渐占据支配地位;在近阈能量范围,上述碰撞机理不再处于支配地位,扭曲效应明显.要完备地描述中低能入射条件下Ar原子的电子碰撞电离过程,理论模型必须同时考虑多种散射机理.  相似文献   

20.
Triple differential cross-sections (TDCS) of a hydrogenic (He+) ion has been studied by positron impact using coplaner geometry for both symmetric and asymmetric kinematics in the intermediate and medium high incident energy region. TDCS has also been studied of He+ ion by electron impact for symmetric kinematics taking account of the electron exchange effect. The final state wavefunction is chosen as the correlated 3-body Coulomb wavefunction satisfying the exact asymptotic boundary condition. The long range Coulomb interaction in the initial channel between the ionic target and the projectile has also been taken into account properly. For positron impact, the collision is found to be almost recoilless at lower incident energies, in contrast to the strong recoil peak noted in the case of electron impact ionisation. For electron impact, the exchange effect is found to be significantly high for equal energy sharing in the final channel. Received 10 July 1999 and Received in final form 7 December 1999  相似文献   

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