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.

Bibliography: pages 56-57. / Angular distributions have been measured for the radiative proton capture reaction ¹²C(p,ϒ)¹³N at beam energies from 40 to 54 MeV. Measurements were made with the new, large anticoincidence-shielded spectrometer HA GAR at angles from 30° to 150° to the beam direction. Differential and total cross-sections have been calculated from these data, and show evidence for resonant behaviour for the transitions to the ground state, the first excited state, and the unresolved second and third excited states. The total cross-sections for these transitions peak at a proton energy of about 46 MeV which is twice the centroid energy of the Giant Dipole Resonance (GDR) based on the ground state of ¹³N.

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