Pairing-energy coefficients of neutron-rich fragments in spallation reactions

Abstract

The ratio of pairing-energy coefficient to temperature (ap/T ) of neutron-rich fragments produced in spallation reactions has been investigated by adopting an isobaric yield ratio method deduced in the framework of a modified Fisher model. A series of spallation reactions, 0.5A and 1A GeV 208 Pb + p, 1A GeV 238 U + p, 0.5A GeV 136 Xe + d, 0.2A, 0.5A and 1A GeV 136 Xe + p, and 56 Fe + p with incident energy ranging from 0.3A to 1.5A GeV, has been analysed. An obvious odd-even staggering is shown in the fragments with small neutron excess (I ≡ N −Z), and in the relatively small-A fragments which have large I. The values of ap/T for the fragments, with I from 0 to 36, have been found to be in a range from -4 to 4, and most values of ap/T fall in the range from -1 to 1. It is suggested that a small pairing-energy coefficient should be considered in predicting the cross sections of fragments in spallation reactions. It is also concluded that the method proposed in this article is not good for fragments with A/As > 85% (where As is the mass number of the spallation system).

Thermodynamics of pairing transition for Odd-A nuclei

“…In particular, the study of thermodynamics is essential for compound nuclei, heavy ion collisions and induced fusions [1][2][3][4][5]. Studies have shown that the pairing correlation plays a very important role in these phenomena and other nuclear thermodynamic properties [6], such as the shape transition in hot nuclei [7,8], the phase diagram structure of liquid-gas phase transition [9,10], and the fragments produced in spallation reactions [11].…”