The Loosely ­Bound Proton in 13 N and the Transfer Reaction 11 B (13 N, 12 C) 12 C

Abstract

The radioactive nucleus 13 N (t 1/2 = 10 min, J ß = 1/2) contains one loosely bound proton (Sp = 1.94 MeV) which can be considered to be bound to a core of 12 C. Taking advantage of the recent availability of beams of radioact­ive nuclei at Louvain-­la-­Neuve, Belgium, a beam of 13 N has been used to in­ vestigate the transfer reaction 11 B( 13 N, 12 C) 12 C. Particle­-γ coincidence data was taken, using the LEDA silicon strip array and BaF2 modules, gating on the 15.11 MeV γ-­decay from the T = 1 state in 12 C*. Two final states, corresponding to 12C gs + 12C* (15.11 MeV) and 12 C* (4.44 MeV)+ 12C* (15.11 MeV) have been ob­served and angular distributions have been measured for both transitions at each of two beam energies, 29.5 MeV and 45 MeV. The results are discussed with special reference to the loosely bound nature of the valence proton in 13 N; the transfer reaction has been modelled using a DWBA code, with the 13N ground state constructed as a mixture of states: a p 1/2 pro­ton bound to 12C gs , or a p 3/2 proton bound to 12 C* 2+ (4.44 MeV). Fits to the experimental data have been obtained using a very shallow set of optical poten­ tials, which are found to be energy dependent. The agreement with experiment is good, with the exception of the 12C* (4.44)+ 12 C*(15.11) transition at the lower beam energy, which is significantly under­estimated by the calculations, suggest­ ing a contribution from a different reaction mechanism.