Influence of energetics on the thresholds of heavy ion transfer reactions
2014 The possibility of sub-barrier transfers is discussed from the point of view of the energetics of the reaction. The position of the entrance channel potential energy curve Vi(R) relative to that of the exit channel corrected for the mass balance Vf(R) Qgg appears to be crucial. When the former curve is situated above the latter one, the transfer is energetically probable and will occur as soon as the colliding nuclei are sufficiently close to each other, i.e. for sub-barrier incident energies. Experimental examples are given. Considerable experimental and theoretical attention has recently been centered on questions that relate to thresholds of nuclear reactions and to the interaction barrier [1-5]. However, the notion of interaction barrier is still not quite clear. Generally, the interaction barrier is defined as the value Bi at which the interaction potential (nucleon + Coulomb) for the s-wave passes through a maximum; but this must be regarded as a strong interaction barrier, or a fusion barrier and some nuclear reactions, namely transfer reactions can take place at incident energies somewhat lower than Bi. The above definition, however, will be adopted here, and in considering the possibility of sub-barrier reactions, we shall ask the following question : for a given projectile target system, can one predict whether or not a given transfer reaction will occur with significant cross section for incident energies lower than Bi ? This question will be studied here from the point of view of the energetics involved in the reaction, which have been shown, in previous studies [6-13], to play a fundamental role. Many authors have underlined the influence of the Q value on reaction probabilities, (*) Laboratoire de Chimie Nucleaire, Centre d’Etudes Nucleaires de Bordeaux, 33170 Gradignan, France. and the enhancements of transitions for which Q = Qopt, where , e~ = E. Z3 Z4 1 1 Qopt 1 2 1 (1) Ei being the c.m. incident energy, Zl Z2 the atomic numbers of the colliding nuclei and Z3 Z4 those of the transfer products [6-9]. Others [10-11] have discussed the dramatic influence on the transfer cross sections of Qgg AP~, Qgg being the Q’value for a ground state transition, and d Y~ the difference between the Coulomb energies in the final and initial states A~ = Ve ~,. Similar ideas are involved in the present paper, but firstly we shall focus on the feasibility of subbarrier reactions, and secondly we shall include a ’ nuclear part in addition to Pc in the expression for the interaction potential. This nuclear contribution may have a non negligible influence for incident energies slightly lower than the interaction barrier. 1. Experimental evidence. Let us consider the two systems 14N + 209Bi and 160 + 209Bi. In figures 1 and 2 are shown the experimental excitation functions obtained by activation techniques [14, 15] for 21 opo and 211 At which correspond respectively to transfers of 1 and 2 protons from the projectile Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyslet:0197500360305900
On some regularities in multinucleon transfer reactions with heavy ions
Abstract Multinucleon transfer reactions have been investigated by bombarding 232 Th and 197 Au targets with 137 MeV 16 O ions. An exponential yield dependence on the Q -values was observed for nucleon exchange reactions.
DWBA analysis of the heavy ion induced transfer reaction
Abstract The heavy-ion induced transfer reactions have been analysed using the finite-range DWBA. The following reactions are treated for incident energies near the Coulomb barrier: 14N(14N, 13N) 15N, 12C(16O, 16O)12C, 11B(16,, 15N)12C and 27Al(16O, 15N)28Si. In most cases the transfered particle is assumed to be bound in a harmonic oscillator potential well. Part of the calculations has been performed for a simple shell model with the Woods-Saxon potential. Good agreement with experiments can be obtained for reactions involving one-nucleon transfer. For the α-particle transfer process, the calculation shows complicated angular distributions, depending on various parameters.