Reaction channel contributions to the triton optical potential

Keeley, N and Mackintosh, Raymond (2020). Reaction channel contributions to the triton optical potential. Physical Review C, 102(6), article no. 064611.

DOI: https://doi.org/10.1103/PhysRevC.102.064611

Abstract

Background: Well-established coupled-channel (CC) and coupled reaction channel (CRC) processes make contributions to elastic scattering that are absent from local density folding models. Little is known concerning the contribution of these processes to ³H optical model potentials. For studying such processes, spin-saturated closed-shell nuclei such as ¹⁶O and ⁴⁰Ca are particularly suitable target nuclei and the (³H,⁴He) reaction is easily handled within conventional reaction theory since it avoids complications such as breakup.

Purpose: To establish and characterize the contribution to the ³H-nucleus interaction generated by coupling to proton pickup (outgoing ⁴He) channels; we also study the contribution of collective states and identify effects of dynamical nonlocality due to these couplings.

Methods: CRC calculations, with CC coupling to collective states, provide the elastic channel S matrix S_lj resulting from the included processes. Inversion of S_lj produces a local potential that yields, in a single channel calculation, the elastic-scattering observables from the CC/CRC calculation. Subtracting the bare potential yields a local and l-independent representation of the dynamical polarization potential (DPP). From the DPPs due to a range of channel couplings the influence of dynamically generated nonlocality can be identified.

Results: Coupling to ⁴He channels systematically induces repulsion and absorption in the ³H optical model potential (OMP) and generally a reduction in the rms radius of the real part. The qualitative effects, including the general undularity of the DPPs, are similar for all cases. Such coupling cannot be represented by renormalizing folding model potentials. Evidence is presented for substantial dynamical nonlocality of the induced DPPs. Local equivalent DPPs for individual couplings cannot be added to give the DPP for multiple couplings.

Conclusions: The DPPs presented here further challenge the notion that local density folding models provide a satisfactory description of elastic scattering from nuclei. Coupling to proton pickup channels induces dynamical nonlocality in the ³H OMP with implications for direct reactions involving ³H. Departures from a smooth radial form for the ³H OMP should be found in good fits to suitable elastic-scattering data.