Gamow-Teller Unit Cross Sections for (t,3He) and (3He,t) Reactions

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The proportionality between differential cross sections at vanishing linear momentum transfer and Gamow-Teller transition strength, expressed in terms of the unit cross section (σGT) was studied as a function of target mass number for (t,³He) and (³He,t) reactions at 115 AMeV and 140 AMeV, respectively. Existing (³He,t) and (t,³He) data on targets with mass number 12≤ A≤ 120 were complemented with new and reevaluated (t,³He) data on proton, deuteron, ⁶Li and ¹²C targets. It was found that in spite of the small difference in beam energies between the two probes, the unit cross sections have a nearly identical and simple dependence on target mass number A, for A≥ 12: σGT=109/A⁰.⁶⁵. The factorization of the unit cross sections in terms of a kinematical factor, a distortion factor and the strength of the effective spin-isospin transfer nucleus-nucleus interaction was investigated. Simple phenomenological functions depending on mass number A were extracted for the latter two. By comparison with plane and distorted-wave Born approximation calculations, it was found that the use of a short-range approximation for knock-on exchange contributions to the transition amplitude results in overestimated cross sections for reactions involving the composite (³He,t) and (t,³He) probes.