Atomic effects on nuclear resonance reaction yield curves of aluminium and nickel

Abstract

Aluminium targets evaporated under a variety of conditions all showed a Lewis peak on the thick-target γ-ray yield curves over the Al 27(p, γ)Si 28 resonance reaction at 992 keV. The peaks of all targets prepared at pressures below 4 × 10 −7 mm Hg rose above the plateau to a height of about 10% of the plateau yield. Targets prepared at higher pressures showed smaller peaks. Thick-target yield curves from the Ni 58(p, γ)Cu 59 resonance reaction at 1424 keV showed a Lewis peak which was about 23% abobe the plateau yield. Results indicate that nickel targets are much less susceptible to contamination than aluminium. Yield curves were calculated using an improved collision spectrum which takes into account the electron shells of the atom. These calculated curves fit the experimental data much better than previous calculations which treated the electrons in the target as free. Results from these calculations indicate that the point corresponding to one-half the plateau yield, lies about 120 eV below the resonance energy for aluminium and 125 eV below for nickel. Results also indicate that past methods for experimentally determining energy resolution from thick-target yield curves are in error.