16O analogue states in the 15N(p, n) 15O reaction

Abstract

The excitation function for the total cross section of the 15N(p, n) 15O reaction has been measured in small energy steps from the threshold at 3.78 MeV to 12 MeV (E x ( 16 O) = 15.7−23.2 MeV) using protons from the tandem Van de Graaff at AERE Harwell. The target thickness was varied from 8–50 keV depending on the width of the structure. An activation technique was used, the positons from the decay of 15O being detected by a plastic scintillator. The absolute total cross section was measured at 5.52, 5.68 and 5.75 MeV by counting in coincidence the annihilation quanta from the positon decay, and these values were used to normalize the relative total cross-section curve. About 18 resonances were observed ranging in width from 20 keV to 650 keV; half of them could be identified in energy and width as T = 1 analogues of known states in 16N. Matching these analogues resulted in an isobaric mass difference 16N- 16O of 12.83±0.02 MeV. A summary of the currently available information on spin-parity values of these T = 1 states is given; rather few states have better than a probable assignment.