Analysis of the Total (n,p) Cross Sections Around 14 MeV with the Pre-Equilibrium Exciton Model

Isotopic effects in the (n, p) reaction cross section on heavy targets and the statistical preequilibrium model

“…This result was obtained in an early investigation by Braga-Marcazzan et al [6] by comparing the bulk of experimental (n,p) cross sections on heavy nuclei with simple preequilibrium calculations. However, in [6] no particular attention was paid to the isotopic effect in (n,p) reactions and to the role of preequilibrium emission in explaining this effect. During the last decade the development of experimental techniques and methods [7] has led to more reliable experimental values of the rather small (n, p) cross sections on heavy nuclei (0.1-10 mb).…”

“…The transition rates Jr_+, calculated by using the golden rule and the density of accessible final states corrected for the Pauli principle [8,11], are proportional to the averaged squared matrix element [M] 2. This quantity is expected to behave approximately as ]MI z =K.A-3E -1 (6) where K is a free parameter. However, the present knowledge of the limits of its value makes it possible to give reasonably accurate predictions for the absolute (n,p) cross sections in the framework of the preequilibrium model.…”

Activation Cross Sections for (n, 2n) Reaction on Neodymium, Samarium, Gadolinium and Ytterbium at 14.6 MeV

“…They have given the empirical a-value extracted by comparing the many experimental (n, p) cross section values at 14 MeV with those obtained from integration (5) and this a-value were used for the estimation of the (n, p) reaction in the present calculations, and other parameters used in the present work are exactly the same as those in Ref. (5).…”

“…Hence, we must estimate the (n, a) cross sections from the experimental data. Most of the experimental (n, a) cross sections at rv14 MeV in the rare-earth region were measured to be lrv5 mb<' 5 The each experimental cross section< 46 ) of the (n, d), (n, pn) and (n, an) was reported to be <1mb.…”

“…(5), is given by ( 1) where nP x is the number of particles of type x in an n-exciton state, Dn the depletion factor which represents the fraction of the initial population surviving de-excitation by particle emission prior to the n-exciton state under consideration, s= Y2 the neutron spin, Une the reaction cross section for the incoming particle, m the mass of the emitted particle, c1 the kinetic energy of the emitted particle, u( c1) the inverse reaction cross section for the emitted particle, jMj 2 the averaged value of the square of the transition matrix element, g the single-particle level density, Ec the excitation energy of the compound nucleus, U, the excitation energy of the residual nucleus, n the number of excitons (particles plus holes), and ii the limiting value for n when equilibrium is reached. In the summation, the index n varies in steps of 2 from 3 to ft.…”