Inelastic scattering of 100 MeV protons from Mg and Si using a Ge(Li) total absorption proton counter

A cooled Ge(Li) detector was used as the total absorption proton counter for the energy analysis of 100 MeV protons scattered from targets of enriched magnesium (99.7 % ²⁴Mg) and silicon (natural isotopic composition). A total energy resolution of 400 keV (FWHM) was achieved; it is comparable to the best resolution presently attainable with magnetic spectrometers in the 100-200 MeV energy region. The measurements cover the 10°-60° lab angular region; and angular distributions are presented for 23 peaks in the energy spectra. A qualitative discussion of the excited states which correspond to the observed peaks is based mainly on the shapes of the distributions. Comparisons are made with results from similar experiments at 55 MeV and 185 MeV. Shapes of angular distributions for strongly excited 2⁺, 3^- and 0⁺ transitions are independent of energy, but significant differences exist for 4⁺ transitions. The excitation of a previously unknown level in ²⁸Si at 11.45±0.12 MeV energy has been observed. The level most probably has J^π = 5^-.