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1.
The dependence of the fusion reaction on the nuclear shell structure was investigated for the two reaction systems 82Se + 138Ba and 82Se + 134Ba, where the nucleus 138Ba has a closed neutron shell N=82, while the nucleus 134Ba has a neutron number 78. Evaporation residues for these fusion reactions were measured near the Coulomb barrier region. The measured evaporation residue cross sections for the reaction system 82Se + 138Ba were two orders of magnitude larger than those for the reaction system 82Se + 134Ba in the excitation energy region of 20–30 MeV. The evaporation residue cross sections were compared with those of the other reaction systems that produce the same compound nucleus as the present systems. It was found that the fusion reaction 82Se + 138Ba occurs without hindrance, while that of 82Se + 134Ba is considerably hindered, as commonly observed in the massive reaction system with the charge product Z p Z t >1800 of projectile and target. This suggests the importance of the shell closure N=82 in the heavy-ion fusion reaction. 相似文献
2.
《Physics letters. [Part B]》1987,196(2):122-125
Probabilities for K-shell ionization prior to fusion (half-trajectory collisions) are determined for 51V, 59Co, 62Ni target atoms and 4.5 MeV/u 40Ar projectiles. Also measured are energy shifts of the Kα and Kβ X-ray lines of residue atoms resulting from multiple inner shell ionization. 相似文献
3.
R. V. Jolos A. K. Nasirov G. G. Adamian A. I. Muminov 《The European Physical Journal A - Hadrons and Nuclei》2000,8(1):115-124
The effect of shell structure on the distribution of the excitation energy between fragments of the deep inelastic collisions
is analysed in the microscopic approach. It is shown that the density of the single-particle levels of the proton and neutron
subsystems near the Fermi surface determines the ratio between the excitation energies of fragments at the initial stage of
the collision. It is shown also that the shell structure strongly influences the correlations between the width of the charge
distributions and the total kinetic energy losses. Calculations are performed for the 40,48Ca+248Cm reactions. The results obtained suggest a possible interpretation for the observed concentration of the excitation energy
in the light fragment in deep inelastic collisions for a wide range of the total kinetic energy losses.
Received: 27 July 1999 / Accepted: 29 March 2000 相似文献
4.
Claudie Gerschel 《Nuclear Physics A》1982,387(1):297-312
A review of incomplete fusion reactions is given. The localization of the entrance chanel angular momentum window is discussed for incident energies lower than 10 MeV per nucleon and is found to depend on the target deformation. With deformed target “peripheral” collisions are observed with ? values in the vicinity of ?cr for complete fusion, while for spherical targets, the ? window is centered around values lower than 0.5 ?cr. These properties are discussed on the grounds of available theoretical models. All other properties of the reactions such as cross sections, angular distributions, shape of the energy spectra of light ejectiles are discussed to bring additional informations about the reaction mechanism. 相似文献
5.
6.
《中国物理C(英文版)》2017,(6)
The role of positive Q-value neutron transfers in sub-barrier fusion reactions has been studied with a modified quantum coupled channels model with all order couplings(CCFULL model). Neutron rearrangement related only to the dynamical matching condition with no free parameters is implemented in the model, which provides a way to understand especially the Q-value dependence of sub-barrier fusion reactions. The fusion cross sections of the collision systems ~(40)Ca+~(94,96)Zr have been calculated and analyzed. The general trend of experimental data can be reproduced well with additional channels for neutron rearrangement. We find that enhancement of sub-barrier fusion cross sections is closely related to the Q-value of the transferred neutrons, in particular for channels with sequential even number transferred neutrons. 相似文献
7.
《Physics letters. [Part B]》1988,201(1):22-24
We introduce an operational measure for the enhancement of the fusion cross section at sub-barrier energies in terms of an asymptotic energy shift ΔE. It is shown that ΔE has a continuously growing trend with the size of the system. This trend is explained in terms of neck formation using the liquid-drop model. Deviations from this trend are attributed to strong coupling to specific channels. 相似文献
8.
A coupled-channel framework for fusion reactions is considered where an ingoing-wave boundary condition allows the effect of strong coupling in the barrier region to be studied. It is shown analytically within the sudden limit and, more generally, with model calculations that the couplings to reaction channels act to enhance the transmission through the barrier at low energies. This appears to be a natural mechanism for explaining the relatively large sub-barrier heavy-ion fusion cross sections which have recently been observed. 相似文献
9.
Formation and evolution of dinuclear systems in reactions of complete fusion are considered. Based on the dinuclear system concept, the process of compound nucleus formation is studied. Arguments confirming the validity of this concept are given. The main problems of describing the complete fusion in adiabatic approximation are listed. Calculations of evaporation residue cross sections in complete fusion reactions leading to formation of superheavy nuclei are shown. Isotopic trends of the cross sections of heavy nuclei formation in complete fusion reactions are considered. 相似文献
10.
Subbarrier fusion reactions in which one constitutent is deformed and aligned are considered in the framework of a coupled-channel model with incoming-wave boundary conditions. The effect of alignment on the fusion cross section is estimated to be 40% for aligned 165Ho. The semiclassical analog to the coupled-channel equations is developed, yielding an expression for the cross section in terms of a weighted average over all orientations of the deformed nucleus. 相似文献
11.
《Nuclear Physics A》1987,467(1):136-148
Spin distributions are calculated for the 16O + 232Th fusion reaction, taking into account both inelastic and transfer channels. The static deformations of the target play an important role. The calculated cross sections for complete fusion are in good agreement with the measured fission yields, whereas the anisotropies are underpredicted. This indicates that there is a serious inconsistency in the interpretation of the data. 相似文献
12.
The excitation of the giant dipole resonance induced by fusion reaction is studied with N/Z asymmetry in the entrance channel. The time dependent Hartree-Fock solution exhibits a strong dipole vibration which can be associated with a giant vibration along the main axis of the deformed compound nucleus. This dipole motion appears to be nonlinearly coupled to the shape oscillation, leading to a strong modulation of its frequency. These phenomena can be detected in the gamma-ray emission from hot compound nuclei. 相似文献
13.
14.
The angular correlation between two alpha particles evaporated from the compound nucleus is sensitive to the initial spin population, and can thus be used to test the possible existence of angular momentum windows in the fusion cross section. A model calculation performed for the 28Si + 28Si fusion reaction at Ecm = 60 MeV is used as an illustration. 相似文献
15.
B. S. Ishkhanov M. E. Stepanov T. Yu. Tretyakova 《Bulletin of the Russian Academy of Sciences: Physics》2014,78(5):405-411
Existing experimental data allow us to study the behavior of nuclear shell structure by analyzing characteristics of different nature. In this work, one of the most striking phenomena of nuclear dynamics is examined: nucleon pairing. Nucleon pairing for different nuclei chains as a function of the number of protons or neutrons in a nucleus explains why high numbers of states with positive parity in even-odd nuclei are observed for excitation energies E* < 4 MeV that form the multiplet of a nucleus’s ground state. 相似文献
16.
K.D. Hildenbrand H. Freiesleben A. Gobbi U. Lynen A. Olmi H. Sann E.C. Wu 《Nuclear Physics A》1983,405(1):179-204
A kinematically complete study of the symmetric systems 144Sm+144Sm and 154Sn+154Sm has been performed at energies 30% in excess of the interaction barrier. They have been chosen because of their different internal structure: 144Sm has a closed N = 82 neutron shell and a spherical ground-state configuration; 154Sm with ten neutrons outside this shell is strongly deformed. The observed gross features of both reactions like energy, angular and total mass or element distributions are very similar; the ratio of the mass variances as function of the total kinetic energy loss indicates the number of exchanged nucleons to be comparable in all stages of the reactions. At small energy losses, however, the element distributions of the 144Sm + 144Sm reaction are considerably broader, pointing at an enhanced proton transfer at the cost of the number of exchanged neutrons in this system. This observation is attributed to the influence of the closed shell which seems to block the transfer of neutrons at low excitation energies. These results can be explained quantitatively by the different gradients of the shell-corrected potential energy surfaces of the two systems. 相似文献
17.
The symmetric and asymmetric fusion reaction systems forming the same compound nuclei 26Al,30Si,38Ar and 170Hf are investigated with the frame of improved isospin dependent quantum molecular dynamics model.The entrance channel mass asymmetry dependence of compound nucleus formation is found by analyzing the shell correction energies,the Coulomb barriers and the fusion cross sections.The calculated fusion cross sections agree quantitatively with the experimental data.The results indicate that compound nucleus formation is favorable for the systems with larger mass asymmetry because of the smaller Coulomb contribution to the fusion barrier. 相似文献
18.
The symmetric and asymmetric fusion reaction systems forming the same compound nuclei ^26Al, ^30Si, ^38Ar and ^170Hf are investigated with the frame of improved isospin dependent quantum molecular dynamics model. The entrance channel mass asymmetry dependence of compound nucleus formation is found by analyzing the shell correction energies, the Coulomb barriers and the fusion cross sections. The calculated fusion cross sections agree quantitatively with the experimental data. The results indicate that compound nucleus formation is favorable for the systems with larger mass asymmetry because of the smaller Coulomb contribution to the fusion barrier. 相似文献
19.
The fusion hindrance,which is also denominated by the term extra-push,is studied on mass-symmetric systems by the use of the liquid drop model with the two-center parameterization.Following the idea that the fusion hindrance exists only if the liquid drop barrier(saddle point) is located at the inner side of the contact point after overcoming the outer Coulomb barrier,the reactions in which two barriers are overlapped with each other are determined.It is shown that there are many systems where the fusion hi... 相似文献
20.
G. P. Pokhil V. V. Cherdyntsev 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2008,2(2):234-236
It is shown that an abrupt change in ionization potential at the transition from one shell to the next one can result in a repeated transition from the heating of channeled ion beam to the cooling and vice versa with an increase in ion velocity. 相似文献