Role of neutrons in the fusion of nuclei
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CLEI Theory
Role of Neutrons in the Fusion of Nuclei V. I. Zagrebaev and V. V. Samarin1) Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia Received March 10, 2006; in final form, October 11, 2006
Abstract—The problem of a quantum-mechanical description of a near-barrier fusion of heavy nuclei under conditions of a strong coupling of their relative motion to neutron degrees of freedom is studied. New ¨ mutually complementing efficient models employing the multidimensional time-dependent Schrodinger equation and methods for numerically solving the problems in question within these models are proposed. This makes it possible to study the evolution of wave functions for outer neutrons and to calculate nucleontransfer probabilities and occupation numbers for quasimolecular states over the entire energy range, including that of deep-subbarrier energies. It is shown that the valence-neutron wave functions extend over the volumes of both colliding nuclei before their surfaces come into contact and even before these nuclei overcome the Coulomb barrier (collectivization of outer nucleons). This gives rise to a substantial neutron-transfer effect on the fusion of nuclei and, in particular, to a sizable increase in the probability of subbarrier fusion for specific combinations of nuclei. PACS numbers: 25.70.Jj, 25.70.Hi, 24.10.Eq DOI: 10.1134/S106377880706004X
INTRODUCTION It is well known that neutron-transfer cross sections are rather large in the case of near-barrier heavy-ion collisions, this being due to a considerable extension of wave functions describing outer neutrons from the highest filled shells (we refer to these neutrons as valence neutrons). Because of this, there is the prevalent opinion that nucleon exchange may affect strongly the probability of the subbarrier fusion of nuclei (see, for example, [1] and numerous references therein). However, the role of neutron transfers has not yet been clarified conclusively, although the enhancement of subbarrier fusion owing to the rotation of deformed nuclei and nuclear-surface vibrations has received a detailed study, both from the experimental and from the theoretical point of view. There are two reasons for this. First, an experimental investigation of the role of nucleon exchanges requires comparing fusion cross sections for different combinations of nuclei, which possess, among other things, different collective properties; therefore, the problem of isolating the specific role of neutrons in the total effect of the enhancement of subbarrier fusion is nontrivial. Second, it is very difficult for many reasons to take exactly into account nucleon-transfer channels within the consistent channel-coupling method, which is successfully used to describe collective excitations in near-barrier processes involving the 1)
Cheboksary Cooperative Institute, Cheboksary, Russia.
fusion of heavy nuclei [2, 3]. As a result, we are still far from a complete understanding of the role of neutrons. Moreover, there is presently no consensus on the significance of neutron trans
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