Proton radiative capture to 13N in the region of the second harmonic giant dipole resonance collective excitation

Abstract

This work embraces the measurement of angular distributions and excitation functions for proton radiative capture to the ground and excited states of 13N, in energy steps from E p = 40 to E p = 52MeV. Legendre polynomial fits to the angular distributions are made and the energy variation of Legendre coefficients is established for several (p, 7 ) transitions involving states up to an excitation energy of 15 MeV. The polynomial coefficients are explained by large dipole-quadrupole interference effects, particularly interesting at excitation energies corresponding to twice (£„ ~ 46 MeV) the centroid value of the ground state based Giant Dipole Excitation. Broad resonances are found in the (p,7o) &nd the (p, 72+3) channels, which involve final states that are members of the same rotational band and therefore should present very similar internal structures as the almost equivalent Legendre coefficients substantiate. For other excited states similar trends have been found although within limits imposed by larger experimental errors. The 2hw -+ Ihuj transition is found largely superimposed on inelastic proton scattering channels, contrary to what was established in previous experiments. Upper limits for the excitation functions are extracted and only for the highest measured energy point are the two contributions clearly separated. This reasearch program is based on a newly-developed anti-coincidence large-volume scintillation spectrometer designed by means of a Monte Carlo simulation code. Sp jcific tests performed with Tandem accelerator beams, and routine application at higher energies, demonstrate the excellent correspondence of the design expectations with the performance as measured, for this spectrometer.