Off-shell effects in (d,p) stripping reactions and the three body system

Abstract

<p>The importance of off-shell effects has been investigated in (d,p) stripping reactions and the model triton.</p> <p>For the stripping reactions a formalism is developed for calculating differential cross-sections and angular distributions assuming a direct process. By taking into account the off-shell background term and its interference several levels in the reaction ¹⁵N(d,p)¹⁶N (unbound) have been interpreted. Contributions to the resonances from other sources are considered by extending the coupled channel theory off the energy shell. In three soluble two-channel models, with square well, δ-function and non-local interactions, the off-shell resonance and bound state behaviour is discussed. The off-shell T-matrix for nuclear reactions is also derived using the R-matrix theory and it is discussed in some numerical detail.</p> <p>For the model triton the ground state energy for two classes of potentials, a rank two and a partly non-local have been calculated. All these potentials fit the low energy data but in addition they support a continuum bound state (CBS). In each class two sets of potentials, one with a continuum bound state k = 5 fmˉ¹ the other at k = 7 fmˉ¹ have been investigated. The rank-two potentials produce a triton ground state collapse in all cases. The binding increases as the CBS moves to higher energies and decreases when the repulsive form factor becomes stronger.</p> <p>The partly non-local potentials combine long-range locality with a short range non-locality. Though their non-local parts acting alone produce a collapse no collapse has been found for the total interactions. In fact the binding is almost the same as that of the local potential acting alone.</p>