Production of long-lived isomers by 4 MeV endpoint energy bremsstrahlung

Abstract

Long-lived isomers of87Sr,103Rh,111Cd,113,115In,117Sn,176Lu,189Os,193Ir and195Pt were produced by means of bremsstrahlung from a 4 MeV endpoint energy 25µA intensity electron beam. Isomeric activities were measured by gamma-spectrometry. Photoexcitation exhibits a steep rise as compared to lower energy excitations of prior experiments by high activity137Cs,60Co,142Pr and24Na sources. The large variety in the magnitude of the excitation cross section may mostly arise from largely differing isomer ratios governed by spin differences between isomeric and ground levels, and likely by differences in the multipole character of the upward transitions, too. Isomer excitation seems to exhibit loose correlations with the product of photoabsorption cross section and isomer ratio derived from (n,n′) reactions on the one hand, and with the product of valence proton and neutron numbers and isomer ratio on the other hand.