Multi-step processes in heavy-ion induced single-nucleon transfer reactions

TL;DR

This paper demonstrates that including multi-step transfer paths, especially via excited states, significantly improves the theoretical description of heavy-ion induced single-nucleon transfer reactions, resolving previous discrepancies.

Contribution

The study explicitly shows that incorporating two-step transfer paths via excited states enhances the accuracy of reaction modeling, particularly for single-proton transfer reactions.

Findings

Two-step transfer via the 4.44-MeV 2+ state improves data description.

Inclusion of similar paths for neutron transfer has minor effects.

Coupled channel calculations outperform FR-DWBA for certain reactions.

Abstract

It was first noted during the 1970s that finite-range distorted wave Born approximation (FR-DWBA) calculations were unable satisfactorily to describe the shape of the angular distributions of many single-proton (and some single-neutron) transfer reactions induced by heavy ions, with calculations shifted to larger angles by up to ~ 4 degrees compared with the data. These reactions exhibited a significant mismatch, either of the reaction Q value or the grazing angular momentum of the entrance and exit channels, and it was speculated that the inclusion of multi-step transfer paths via excited state(s) of the projectile and/or ejectile could compensate for the effect of this mismatch and yield good descriptions of the data by shifting the calculated peaks to smaller angles. However, to date this has not been explicitly demonstrated for many reactions. In this work we show that inclusion of the two-step transfer path via the 4.44-MeV 2+ excited state of the 12C projectile in coupled channel Born approximation calculations enables a good description of the 208Pb(12C,11B)209Bi single-proton stripping data at four incident energies which could not be described by the FR-DWBA. We also show that inclusion of a similar reaction path for the 208Pb(12C,13C)207Pb single-neutron pickup reaction has a relatively minor influence, slightly improving the already good description obtained with the FR-DWBA.