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1.
Fragment angular distributions in fission is one of the oldest and well understood aspects of fission theory. However, recent
heavy ion-induced fission and fission-like reactions have added a new dimension to this problem. We review here our present
understanding of the fragment angular distribution theory in fission and fission-like reactions. 相似文献
2.
使用Monte-Carlo模拟计算了垒下16O+232Th系统转移裂变和复合核裂变碎片角分布及角关联.转移过程、熔合过程和裂变过程分别用半经典模型、耦合道模型及鞍点过渡态统计模型进行模拟.考虑了各物理量分布产生的运动学效应及裂前中子发射和裂后碎片粒子蒸发对碎片角分布及角关联的影响.模拟结果和实验测量的分布相一致.使用折叠角技术借助Monte-Carlo模拟区分转移裂变和复合核裂变是可能的.考虑了转移裂变和裂前中子发射的影响,复合核裂变碎片角分布各向异性异常仍然存在. 相似文献
3.
The fission fragment angular distributions have been measured for the neutron fission of 232Th at a number of energies near the neutron threshold. An exhaustive search has been made for a set of transition states and barrier parameters that would simultaneously fit the angular distributions and reproduce quantitatively the structure seen in the neutron fission cross section. No satisfactory fit to both types of data could be obtained with a double-humped fission barrier. However, use of a triple-humped fission barrier does provide a reasonable fit to all the experimental data. 相似文献
4.
《Physics letters. [Part B]》1988,207(4):385-388
Fragment angular and mass distributions have been measured simultaneously for photon energies near the fission barrier of 236U. Different angular distributions have been observed for particular fragment mass regions. This establishes a clear relationship between the quantum numbers of the transition states and the fragment mass division. The results are discussed within the transition channel concept of the double humped barrier for different fission paths and the more recent model of multi-ecit channels. 相似文献
5.
S. G. Kadmensky 《Physics of Atomic Nuclei》2002,65(10):1785-1794
On the basis of a generalization of integral formulas for nuclear-decay widths to the three-body case, the spontaneous and the low-energy induced ternary fission of nuclei are investigated by using the adiabatic approximation. The properties of energy distributions, of partial fission widths, and of the angular distributions of fission fragments are analyzed for the case of ternary fission. Conditions are found under which the angular distributions of two heavy fragments originating from ternary fission are similar to the analogous distributions of fragments originating from binary fission. The features of angular distributions are investigated, along with the parities and angular momenta of the third (light) ternary-fission fragment. 相似文献
6.
The angular distributions of fragments originating from the binary fission of odd and odd-odd nuclei capable of undergoing spontaneous fission that are polarized by a strong magnetic field at ultralow temperatures and from the low-energy photofission of even-even nuclei that is induced by dipole and quadrupole photons are investigated. It is shown that the deviations of these angular distributions from those that are obtained on the basis of the A. Bohr formula make it possible to estimate the maximum relative orbital angular momentum of fission fragments, this estimate providing important information about the relative orientation of the fragment spins. The angular distributions of fragments originating from subthreshold fission are analyzed for the case of the 238U nucleus. A comparison of the resulting angular distributions with their experimental counterparts leads to the conclusion that the maximum relative orbital angular momentum of binary-fission fragments exceeds 20, the fragment spins having predominantly a parallel orientation. The possibility is considered for performing an experiment aimed at measuring the angular distributions of fragments of the spontaneous fission of polarized nuclei in order to determine both the spins of such nuclei and the maximum values of the relative orbital angular momenta of fission fragments. 相似文献
7.
S S Kapoor 《Pramana》1989,33(1):13-20
This article gives an overview of the physics of the fission phenomenon. It provides a brief introduction to the various aspects
of the fission process such as liquid drop model fission barriers, different stages of the fission process, fragment kinetic
energy and mass distributions, nuclear shell effects on fission barriers, fragment angular distributions and rare fission
modes. 相似文献
8.
D.J. Morrissey G.J. Wozniak L.G. Sobotka R.J. McDonald A.J. Pacheco L.G. Moretto 《Nuclear Physics A》1985,442(3):578-604
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. 相似文献
9.
LIU Guo-Xing CHEN Ke-Liang ZHENG Ji-Wen WANG Su-Fang BAI Xing-Ping YU Xian FAN Zhi-Guo 《中国物理C(英文版)》1989,13(8):733-739
The angular distributions of fission fragments for a series of compound nuclei formed in the bombardment of 181Ta,197Au Pb and 209Bi by 12C ions and in the bombardment of natural lead by 14N ions were measu ed with mica track detectors and gold surface barrier detectors.It is shown that all experimental data for the fission fragment angular distributions can be fitted by the statistical scission model of fission fragment angular distribution. 相似文献
10.
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. 相似文献
11.
12.
Systematic studies of heavy-ion induced fission reactions at near-barrier energies carried out in the last decade have brought
out many interesting aspects of fission process in general. The recent experimental findings which show dependence of fission
fragment angular distributions on entrance channel, shape, size and spin of the interacting nuclei and shell closure of the
intermediate compound nucleus are summarised in the present paper. 相似文献
13.
Liu Zuhua Xu Jincheng Zhang Huanqiao Qian Xing Qiao Yu Lin Chengjian Xu Kan 《中国物理C(英文版)》1994,18(6):489-495
We have succeeded in isolating the complete arising from complete fusion-fission in terms of the fragment folding angle technique,and measured complete fusion-fission cross sections and fragment angular distributions for the 16O+232Th system in the center-of-mass energies between 72.61 and 80.11 MeV.The observed fission excitation function is in quite good agreement with the expectation of the coupled-channels theory.However,the measured fragment angular distributions are more anisotropic than the predictions of both the saddle-point transition-state model and scission model. 相似文献
14.
The gridded ion chamber developed at CBNM provides a powerful tool for measurements of fission fragment angular, kinetic energy and mass distributions with an angular efficiency close to 4π. In the present experiment it is used together with a neutron time-of-flight detector to measure the correlation between neutron emission, fragment angle, mass and energy in the spontaneous fission of 252Cf. 相似文献
15.
Measurements have been made, by means of mica nuclear track detectors, of the distributions in tracklength and the angular distributions with respect to the beam direction for the fission fragments from the systems Ag, Te and Au plus 80-MeV alpha particles. Analysis of the tracklength distributions indicated that, in each case, full momentum transfer from the incident projectile characterized those interactions that led to fission. Angular-momentum dependent statistical model calculations for the decay of the respective compound nuclei then provided information on fission-evaporation competition in the de-excitation processes, and in particular the distribution in nuclear temperature and angular momentum at which the fission events took place. This information was then employed in the analysis of the measured fission fragment angular distributions, and to extractK 0 2 values. From these, the moments of inertia of the fission saddle point shapes were calculated, and the results are in good agreement with theoretical estimates. 相似文献
16.
A. S. Vorobyev A. M. Gagarski O. A. Shcherbakov L. A. Vaishnene A. L. Barabanov 《JETP Letters》2016,104(6):365-373
New results of the neutron-induced fission experiments carried out at the neutron time-of-flight spectrometer GNEIS of the PNPI are given. Angular distributions of fission fragments from the neutron-induced fission of 233U and 209Bi nuclei have been measured in the energy range 1–200 MeV using position sensitive multiwire proportional counters as fission fragment detector. The recent improvements of the measurement and data processing procedures are described. The data on anisotropy of fission fragments deduced from the measured angular distributions are presented in comparison with the experimental data of other authors. 相似文献
17.
Satya Prakash 《Pramana》1989,33(1):109-131
This article summarizes the recent radiochemical investigations on mass, charge kinetic energy and fragment angular distributions
in low energy fission of actinides. 相似文献
18.
R. Kalpakchieva Yu. Ts. Oganessian Yu. E. Penionzhkevich H. Sodan 《Zeitschrift für Physik A Hadrons and Nuclei》1977,283(3):253-256
The mass distributions and total c.m. kinetic energies of fission fragments formed in the reaction40Ar+243Am at bombarding energies of 214, 222, 240 and 300 MeV have been measured using the angular correlation method. Angular distributions and anisotropy for 222 and 300 MeV have also been obtained. A symmetric mass distribution corresponding to the decay of a highly excited compound nucleus was obtained at 300 MeV bombarding energy. However, with decreasing bombarding energy the fission fragment mass distribution becomes asymmetric, the most probable heavy fragment mass being about 200–210 amu. 相似文献
19.
Bivash R Behera Subinit Roy P Basu M K Sharan S Jena M Satpathy SK Datta L Satpathy ML Chatterjee 《Pramana》1999,53(3):563-566
Time of flight and energy of fission fragments were measured using pulsed beam. Fission fragment mass and energy integrated
angular distributions were extracted. Fission fragment anisotropy was explained in the framework of saddle point model. 相似文献
20.
Fission fragment angular distributions have been observed in electron-induced fission of 232Th for electron energies 8.7 MeV ≦ Ee ≦ 30 MeV. For low energies (though above the fission threshold) the angular distributions contain both a dipole and a quadrupole component. The (90°/0°) anisotropy decreases rapidly for higher electron energies but reveals smaller peaks after the onset of second-, third- and fourth-chance fission suggesting that the effective fission barriers for 231Th and 229Th in second- and fourth-chance fission, respectively, are both characterized by . 相似文献