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.



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 Slj resulting from the included processes. Inversion of Slj 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.

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