Prediction of the high-spin selectivity of compound reactions induced by heavy ions

Abstract

Two procedures are described to predict the selectivity of heavy-ion (HI) compound reactions for excitation of high spins. The applicability of statistical-model calculations in respect to yrast line effects is discussed. Contour diagrams of the total cross sections σ(E ∗, I), dσ(E ∗, I)/ dE ∗ and dσ(E ∗)/ dE ∗ are derived, yielding the gradient dσ(E ∗, I)/ dI and the p to “background” ratio of high-spin states as well as the “optimum Q-value” for any given HI compound reaction. The dependence of both the optimum Q-value and the shape of dσ(E ∗)/ dE ∗ on the critical L-value at high bombarding energies can be used to determine L crit. This is demonstrated for the reaction 12 C + 14 N → 26 AI . A rougher estimate of the selectivity is given by the “grazing-collision picture” which is based on a consideration of the angular momentum balance. Using the reactions 10B( 12C, d), 12C( 12C, d), 12C( 14N, d), 11B( 14N, p), 13C( 14N, p), 10 B( 14 N, α) and 12C( 14N, 6Li) as examples, the theoretical predictions are shown to be in excellent agreement with experiment, for bombarding energies ranging between 40 and 120 MeV. The possibility to predict the high-spin selectivity is the precondition for an application of HI compound reactions for investigations of yrast lines and converts this class of reactions into an outstanding means for spectroscopy of high-spin states in light nuclei.