PRODUCTION OF LONG-LIVED ISOMERS BY 4 MEV END-POINT ENERGY BREMSSTRAHLUNG

Long-lived isomers of Sr-87, Rh-103, Cd-111, In-113,In-115, Sn-117, Lu -176, Os-189, Ir-193 and Pt-195 were produced by means of bremsstrahlu ng from a 4 MeV endpoint energy 25 mu A intensity electron beam. Isome ric activities were measured by gamma-spectrometry. Photoexcitation ex hibits a steep rise as compared to lower energy excitations of prior e xperiments by high activity Cs-137, Co-60, Pr-142 and Na-24 sources. T he large variety in the magnitude of the excitation cross section may mostly arise from largely differing isomer ratios governed by spin dif ferences between isomeric and ground levels, and likely by differences in the multipole character of the upward transitions, too. Isomer exc itation seems to exhibit loose correlations with the product of photoa bsorption cross section and isomer ratio derived from (n, n') reaction s on the one hand, and with the product of valence proton and neutron numbers and isomer ratio on the other hand.