Isobaric analogue states in (p, n) reactions at 94 MeV

Abstract

Targets of natural Al, Sc, V, Mn, Co, Cu, Nb, Ag, In, La, Ta, Au, Pb and U were bombarded with 94 MeV protons. The neutron energy spectrum from each target was analysed using a time-of-flight spectrometer with a 0.066 ns · m⁻¹ resolution. Neutron energy resolution close to 90 MeV was ≈2 MeV (fwhm). Peaks were observed in the neutron spectra at energies corresponding to the formation of the isobaric analogues of the ground state of the parent nuclei. The angular distributions for these reactions were measured over the angular range 0° to 10°, and the relative cross sections determined in this experiment were normalised to the absolute production cross section of neutrons in the forward direction for the d(p, n)2p reaction.

A limited analysis of the angular distributions in terms of the optical model indicates an isospin-dependent potential somewhat peaked on the surface and having a strength of 40 MeV at 94 MeV. This potential strength is lower than that similarly calculated for protons around 20 MeV and indicates that this potential is energy dependent.