Coupling effects in proton scattering from40Ca

Abstract

Recent studies showed that neutron pickup makes a substantial contribution to the proton optical model potential (OMP) for light, mostly halo, target nuclei. Here, we extend those studies to a more "normal" target nucleus: 40 Ca. We present coupled reaction channel (CRC) calculations with the coupling of 30.3 MeV incident protons to deuterons and up to 12 states of 39 Ca. The proton elastic scattering S matrix from the CRC calculation is subject to S lj → V (r) + l · s V SO (r) inversion and the bare potential of the CRC calculation is subtracted, directly yielding a local and L-independent representation of the dynamic polarization potential (DPP). This is appropriate for comparison with phenomenological OMPs and local OMPs derived in local density folding models. The real-central part of the DPP is repulsive and cannot be represented as a uniform normalization of the bare potential, changing the rms radius. A series of model calculations reveal the dependence of the DPP on a range of parameters illuminating (i) departures of nucleon potentials of specific nuclei from global properties, (ii) the generation of repulsion, and (iii) the requirements for all-order CRC and deuteron breakup. Light is thrown on the nonlocality of the underlying DPP.

Increase in|SL|induced by channel coupling: The case of deuteron breakup

“…The effect is associated with the existence of emissive regions in the imaginary DPP, suggesting a connection with the nonlocal nature of the DPP. The same relationship was previously found for 6 Li scattering, indicating a generic effect bearing on the dynamics of nuclear reactions. …”

“…This WW phenomenon was noted long ago [2] and occurs in other scattering cases, for example, 6 He scattering at energies near the barrier [3][4][5]. In that case, too, emissive regions appear in the imaginary part of the DPP due to breakup (BU).…”

“…In the case of p ↔ d coupling, the other correlate with WW, noted above, the presence of emissive regions in the DPP, occurs only slightly in the surface region; see Ref. [6]. The WW phenomenon appears to be one effect of the nonlocality of the DPP.…”

“…For example, the reaction channel coupling of protons to deuteron channels modifies the proton elastic |S lj | the 'right way.' There appears to be a correlation: with p ↔ d (no WW), the change in total cross section in the elastic channel due to the coupling far exceeds the cross section to the deuteron reaction channels; however, with BU of 6 Li [1], the reverse is the case and the BU cross section is greater than the increase in total reaction cross section that occurs with BU coupling. In the case of p ↔ d coupling, the other correlate with WW, noted above, the presence of emissive regions in the DPP, occurs only slightly in the surface region; see Ref.…”

“…Reference [1] presented a study of the dynamic polarization potential (DPP) due to projectile breakup for 6 Li nuclei scattering from 12 C at energies from 90 to 318 MeV. At the lower energies, and for certain values of partial-wave angular momentum L, the magnitude |S L | of the elastic channel S matrix went the 'wrong way' (WW) when coupling to the breakup channels was switched on, i.e., |S L | increased.…”