Angular distributions of photoprotons from 208Pb

Angular distributions of photoprotons following the (e, e′p) reaction in ²⁰⁸Pb have been measured at incident energies of 25.0 MeV and 40.0 MeV. The proton energy distributions were measured at several angles and the angular distributions were obtained for several proton energy ranges. Proton groups at around 11.0 MeV and 15.3 MeV are separated for the angular distributions and the results show almost isotropic distributions, which indicate that these proton groups are emitted through IAR. The angular distributions for other slowly varying parts of the proton spectra proved strongly asymmetrical, indicative of interference between E1 and E2 transition.     

Fission induced by heavy-ion collisions

Fission fragment angular distributions from sequential fission induced in heavy-ion reactions will depend on the angular momentum exchange occuring in such reactions in considerable detail. Theoretical expressions for the angular distributions of fission products from totally and partly polarized nuclei are presented. They are compared with recent measurements and discussed in relation to the deep inelastic reaction mechanism.     

19F+27Al反应产物的角分布、角分散与耗散机制

完成了114MeV¹⁹F+²⁷Al深部非弹性碰撞产物的角分布测量.分析了反应产物B,C,N,O,F,Ne,Na,Mg和Al的实验室系角分布,讨论了反应形成的中间双核系统随时间演化过程中角分布所表现出的耗散特点.从实验上提取了反应产物各元素的角分散参数并作了角分散参数的理论拟合,讨论了角分散参数的物理意义以及角分散参数与耗散反应产物的电荷数Z之间的依赖关系.     

Direct processes in the6Li(α, d)8Be reaction

The angular distributions of deuterons from the ⁶Li(α, d)⁸Be reaction corresponding to the 0⁺ ground state and the 2.9 MeV (2⁺) state in⁸Be have been measured at E_α = 17.3, 23.3 and 25.1 MeV. The excitation functions for this reaction have been measured at seven emission angles in the region from 12 up to 25 MeV. The experimental angular distributions are compared with theoretical predictions obtained using DWBA stripping calculations and the plane wave approximation (PWA) for various direct processes. It is shown that the experimental angular distributions can be described throughout the angular region using the simple mechanisms associated with the break-up of the ⁶Li target nuc clusters and heavy-particle stripping. The interference of these processes is taken into account.     

THE MASSIVE TRANSFER IN 12C+197Au REACTION

In this paper, we present energy spectra and angular distributions for the α-par-ticles emitted in the reaction of ¹²C+¹⁹⁷Au at 64 and 67 MeV and for α, Be and B emittedin the reaction at 71.5 MeV. The most-probable energles of the variousproducts emittedin this reaction decrease.with decreasing incident energy. The angular distributions peak near grazing angle.The peak position of the angular distributions shift from--80°to--120°while the projec-tile energy decreases from 71.5 MeV to 64 MeV. These all show the features of the transferreaction. The ⁶Li product also has been measured and the ⁸Be particle emitted from thisreaction was detected at 90°to the beam direction using α-α coincident technique at 71.5MeV. The coross section of the ³Be is only few percent at the same angle.     

DEPENDENCE OF THE MECHANISM AND CROSS SECTION OF THE α PARTICLES EMITTED FROM 12C+64Ni REACTION ON INCIDENT ENERGY

Energy spectra and angular distributions of the particles emitted from ¹²C+⁶⁴Ni reaction at eight energies in the region of 36.5MeV—69.4MeV are measured. The angular distributions of α particles change from forward peaked one to that peaked near by the grazing angle with decreasing incident energy. This result show that the emission mechanism of non-evaporation α particle is different in different energy regions.     

Momentum transfer in light-ion-induced fission reactions

Angular correlations and angular distributions of the fission fragments produced in the bombardment of a ²³²Th target with protons, deuterons and α-particles in the energy range between 35 and 1000 MeV/nucleon have been measured. From these measurements, the distributions of linear momentum imparted to fissioning nuclei have been deduced in the various energy regimes; dominating reaction mechanisms are classified according to the fraction of the available incident momentum transferred to the target. The experimental results are compared to the predictions of intra-nuclear cascade calculations. An optimum excitation energy supported by the fissioning nuclei could be the dominant limitation to momentum transfer at high incident energies. The angular distributions of the fission fragments were used to extract fission cross sections and upper limits of the angular momentum imparted to the fissioning nuclei.     

RECOIL STUDY OF RESIDUAL NUCLEI I AND Sb IN THE REACTION INDUCED BY 12C ON 115In

Excitation functions and angular distributions of the residual nuclei I and Sb were measured in the reaction of ¹²C on ¹¹⁵In at energies up to 72MeV using radiochemical techniques. A kinematic analysis of the angular distributions showed probable mechanisms leading to productions of I and Sb isotopes.     

Regge pole analysis of large angle elastic scattering in chemically reactive systems

Complex angular momentum techniques are applied to the theory of elastic scattering in chemically reactive systems. The Watson-Sommerfeld transformation allows the scattering amplitude to be written as a background integral and a sum over Regge Poles in the right-hand complex plane. It is shown the Regge Poles are restricted to the first quadrant for physically meaningful optical potentials. Neglect of the background integral and all poles except for the one closest to the real axis allows the differential cross section for large scattering angles to be written in terms of a Legendre function of complex degree. The theory agrees with experimental results for the elastic angular distributions of direct and complex reactions. It predicts oscillations and a glory in the backward direction of the angular distributions. The oscillations arise from interference between orbiting or surface waves that propagate around the region of chemical reaction. Measurements of angular distributions at different collision energies can be used to determine a Regge trajectory.     

Heavy-ion scattering at low energies: First-order correction to the eikonal phase shift

The first-order non-eikonal correction has been applied to calculate heavy-ion reaction cross sections at low energies. The numerical investigations show that, for many heavy-ion systems, reaction cross sections and elastic scattering angular distributions thus calculated, are in good agreement with the optical model calculations.     

A SEMI-CLASSICAL ANALYSIS ON THE REACTION 12C+209Bi AT BOMBARDING ENERGIES SLIGHTLY ABOVE THE COULOMB BARRIER

For reactions induced by light heavy ion such as ¹²C, at bombarding energy slightly above the coulomb barrier, using semi-classical theory, neglecting macroscopic frictional force, the reaction mechnisms are sorted by the orbital angular momentum of the entrance channel from the classical deflection functions fitting elastic scattering. Moreover, inserting a transfer probability factor representing the Q-Window effect into the semi-classical angular distribution formula of Kalinkin and Grabowski, we obtain a formula for the differential cross-section per unit energy interval. The calculated results, including the elastic scattering angular distributions, energy spectrum and angular distributions of emitted α-particles in quasi-elastic process, complete fusion cross-section, fusion-fission cross-sections and the exitation functions of evaporated neutron, agree with the experimental data on the reaction ¹²C+²⁰⁹Bi reported by our Institute.     

20 MeV以下n+6Li反应的理论计算

核反应R矩阵理论是研究轻核反应以及中重和重核共振能区核反应的重要理论方法。包含能级矩阵非对角元贡献的完全R矩阵理论在理论上比较严格。根据不同的假定和近似得到不同的R矩阵计算方法。新编的R矩阵程序FDRR包含了4种计算方法,包括约化道多能级Breit-Wigner 方法、完全约化R矩阵方法、非对角化能级位移约化R矩阵方法及对角化能级位移约化R矩阵方法。可计算轻核各种两体反应道的截面、角分布。利用FDRR程序对n+6Li 反应20 MeV以下能区进行理论分析和计算,理论计算结果与实验数据进行了比较分析,理论计算得到的截面和角分布与实验数据符合得很好。R-matrix theory is an important theory of light, medium and heavy mass nuclide nuclear reaction in the resonance energy range. Full R-matrix formalism contains the un-diagonal element of energy levels matrix and it is rigorous in theory. Because of different assumptions and approximations, many kinds of R-matrix methods are obtained. The new R-matrix code FDRR is presented and includes 4 kinds of R-matrix methods, reduced multi-level Breit-Wigner R-matrix method, full reduced R-matrix method, un-diagonal energy shift reduced Rmatrixn method, and diagonal energy shift reduced R-matrix method. It can be used for calculating integral cross sections and angular distributions of 2-bodies reactions. The cross sections and angular distributions of n+6Li reaction are calculated and analyzed by FDRR code below 20 MeV. The calculation results are compared with the experimental data, and the cross sections and angular distributions are in good agreement with experimental data.     

Large contribution of deep inelastic processes to reactions of40Ar and48Ca with238U

Differential recoil range distributions have been measured for heavy-reaction products ranging from Te(Z=52) to quasielastic transfer products near the charge and mass of the targets for the reactions of 276 MeV⁴⁸Ca+²³⁸U, 237MeV and 250 MeV⁴⁰Ar+²³⁸U, and 259 MeV⁴⁰Ar+¹⁹⁷Au. The measured recoil range distributions for the⁴⁰Ar+¹⁹⁷Au reaction agree with range distributions calculated from the known projectile-like fragment angular distributions for this reaction. The angular distributions of recoil products formed in the uranium target reactions are deduced and show that the products in the₇₅Re to₈₃Bi region have backward peaked angular distributions characteristic of deep inelastic reactions. The heavy product angular distributions smoothly vary from a (1/sinθ) shape to an exponential shaped backward peak as the atomic number of the product increases from 52 to 83. The trend in the deduced angular distributions for those elements for which recoil range distributions were determined in the⁴⁰Ar+¹⁹⁷Au reaction and the 250 MeV⁴⁰Ar+²³⁸U reaction is similar, suggesting that just as for the Ar+Au system the composite system for the uranium target reaction is also not fully equilibrated along the mass asymmetry coordinate. These conclusions show that the fraction of the total reaction cross section resulting in complete fusion must be re-evaluated for the⁴⁰Ar+²³⁸U reaction and similar heavy-target reactions.     

Angular Distributions and Angular Dispersions of the Dissipative Products in19F+27Al Reaction

Angular distributions of fragments b,c,n,o,f,ne,na,mg and al induced from the reaction of ¹⁹F+²⁷Al have been measured at the beam incident energy of 114mev. the angular distributions and the element distributions at different angles were analyzed to provide an evolution process of the intermediate dinuclear system. the angular dispersion parameters were extracted from the experimental data and compared with the theoretical results. the dynamic dispersions for the dissipative products are not negligible and depend strongly on the charge number Z of the fragments,the deeper dissipation the more dynamic dispersion.     

CDCC Approaches and Roles of Closed Channels in d-Nucleus Reactions

The effect of deuteron breakup in d-nucleus reaction is treated with the continuum discretized coupled channels (CDCC) approach, and the effects on the total reaction cross sections and elastic scattering angular distributions are studied by comparing the calculations of CDCC and spherical optical model with our global deuteron optical potential [Phys. Rev. C 73 (2006) 054605] below 200 MeV, for target nuclei ranging from ¹²C to ²⁰⁸Pb. The contributions from the closed channels to the total reaction and breakup cross sections, and angular distributions of elastic scattering are also seriously discussed.     

Angular distributions and cross-sections of projectile-like fragments in the 19F + 159Tb reaction

The angular distribution of projectile-like fragments (PLFs) in the ¹⁹F + ¹⁵⁹Tb reaction have been measured at beam energy equal to 98MeV. Angular distributions of PLFs showed a systematic change with increasing mass transfer, starting from the peaking at grazing angle for heavier PLFs to very forward peaked angular distributions for lighter PLFs. Cross-sections of the different PLFs were obtained by integrating their centre-of-mass angular distributions. The PLF cross-sections have been compared with the incomplete fusion cross-sections obtained from the earlier measurement of the evaporation residue cross-section. Reduced cross-sections for lighter PLFs were observed to be higher compared to those observed in ¹⁹F + ⁶⁶Zn reaction at similar values of E _cm/V _b. Also, elastic scattering measurements were carried out to get information about the grazing angle and total reaction cross-section.     

Sequential fission angular distributions from mass-asymmetric heavy-ion reactions

The angular distributions of sequential fission fragments have been measured for the reactions of ⁴⁰Ar with ¹⁹⁷Au and ²³⁸U as a function of reaction Q-value and charge transfer. These angular, distributions are used to study the angular momentum and alignment of the deep-inelastic products which undergo fission. All of the fission fragment angular distributions are strongly focused into the plane defined by the beam and the projectile-like fragment velocity vectors. The in-plane angular distributions from reactions with uranium are isotropic for small energy losses and become anisotropic as the energy loss increases. For large negative Q-values, the in-plane anisotropy increases as the deep-inelastic products become more symmetric. The variation of the in-plane anisotropy with mass asymmetry for the two systems in this work was compared to a compilation of previous work and a consistent pattern was found. These alignment data are compared to equilibrium statistical calculations.     

Examination of the <Superscript>16</Superscript>O + <Superscript>28</Superscript>Si system with microscopic and phenomenological potentials

The ¹⁶O + ²⁸Si reaction has been widely studied both experimentally and theoretically and has been claimed to show indications of chaotic scattering. In order to examine this claim and to address whether reaction models such as the optical one could explain the experimental data, we have analyzed the ¹⁶O + ²⁸Si system within the framework of the optical model for ten energies from 29.0 to 45.0 MeV, by using microscopic folded potentials, which are based on M3Y nucleon-nucleon, alpha-alpha effective interactions and a phenomenological shallow potential. All potentials describe the individual angular distributions very well at forward angles. However, they fail to describe the individual angular distributions over the whole angular range up to 180°. Nevertheless, we have been able to explain the experimental data by modifying the surface region of the microscopic real potentials by adding two surface potentials. With these correction potentials, we have obtained very good agreement for the individual angular distributions over the whole angular range for the given energies as well as for the experimental data near the Coulomb barrier. The failure of these optical potentials in explaining the scattering observables of this reaction without corrections puts a question mark on the model and supports the idea of a chaotic behavior. The text was submitted by the authors in English.     

Quasi-free inclusive processes in the two-particle splitting of tritons by deuterons with an energy of 37 MeV

The d + t → d + d + n reaction was experimentally and theoretically investigated at an incident deuteron energy of 36.9 MeV. The experiment was performed on the U-240 isochronous cyclotron at the Institute for Nuclear Research, National Academy of Sciences of Ukraine. Inclusive spectra of deuterons and their angular distributions in the range of 15° ≤ θ_d ≤ 52° were measured. Experimental spectra and angular distributions of the final deuterons from the d + t → d + d + n reaction are satisfactorily described in a diffraction approximation that considers interaction in the final state and the correct asymptotic of the wave function of colliding nuclei. The scattered deuterons are the main contributors to the cross section (up to 70–90%), while the deuterons from tritons can be seen well only at low and high energies, at the edges of the spectra.     

Fragment Angular Distributions of the 600 MeV 40)Ar+197 Au Reaction

The angular distributions of the fragments in the range of 4π solid angle for the 600 MeV ⁴⁰Ar+¹⁹⁷Au reaction have been measured using the beam-off γ-ray spectroscopy technique. The features of the fragment angular distributions and the reaction mechanisms of the production of fragments have been discussed.