GAMMA-DECAY TOWARDS THE SHAPE-ISOMERIC GROUND-STATE OF U-239

In a high-energy-resolution measurement of gamma-rays from neutron cap ture in U-238 five hitherto unknown gamma-transitions could be found e xclusively in the gamma-ray spectra of s-wave neutron subthreshold fis sion resonances around 720 eV. Since it is generally believed that the strongest fission resonance in this cluster at a neutron energy E(n) = 721.6 eV is a nearly pure class-II state, these transitions might be the first experimental observation of gamma-decay populating the shap e-isomeric ground state in U-239. This assumption is supported by a qu antitative analysis of the relative peak areas of each individual gamm a-transition amongst these fission resonances, which show a strong cor relation with the respective class-II admixture into the observed neut ron resonance.