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
Enhancement of two-proton transfer in N = 82 nuclei: A study of 1p, 2p and (2p+2n) transfer reactions induced by 16O on 140Ce, 142Nd and 144Sm near the Coulomb barrier
Abstract One-proton, two-proton, and α-particle transfer have been studied on nuclei with closed neutron shell N = 82 using 16 O beams of 63 to 66.5 MeV incident energy. Transfer probabilities defined in a semiclassical model are derived for the different reaction channels. For this purpose the Q -value and angular dependence of the cross section are discussed. The two-proton transfer to the ground states shows an enhancement by a factor 20–25 compared to other nuclei, showing the effect of the proton pairing in these nuclei (they correspond to equivalent neutron configurations in 108, 110, 112 Sn). The total transfer probability follows a common trend for all three target nuclei as a function of energy above the Coulomb barrier for the proton and two-proton transfer, respectively, but not for the four-nucleon transfer.
Pioneer 10 Observations of the Ultraviolet Glow in the Vicinity of Jupiter
A two-channel ultraviolet photometer aboard Pioneer 10 has made several observations of the ultraviolet glow in the wavelength range from 170 to 1400 angstroms in the vicinity of Jupiter. Preliminary results indicate a Jovian hydrogen (1216 angstrom) glow with a brightness of about 1000 rayleighs and a helium (584 angstrom) glow with a brightness of about 10 to 20 rayleighs. In addition, Jupiter appears to have an extensive hydrogen torus surrounding it in the orbital plane of Io. The mean diameter of the torus is about equal to the diameter of the orbit of Io. Several observations of the Galilean satellites have also occurred but only a rather striking Io observation has been analyzed to date. If the observed Io glow is predominantly that of Lyman-α, the surface brightness is about 10,000 rayleighs.