Discovery of rare neutron-rich Zr, Nb, Mo, Tc, and Ru isotopes in fission: Test of β half-life predictions very far from stability

In experiments employing fast ion-guide-based on-line mass separation we have identified six new, rare nuclides of highly refractory elements produced in the fission of {sup 238}U by 20-MeV protons. The new isotopes {sup 105}Zr, {sup 107}Nb, {sup 109}Mo, {sup 110}Mo, {sup 113}Tc, and {sup 115}Ru were identified through ({beta}, {ital K}{sub {alpha}} x-ray) coincidences and {beta}-delayed {gamma} decay. The observed {beta} half-lives range from 130 ms to approximately 1 s. All our recent {beta} half-life data are compared with predictions of the deformed quasirandom-phase-approximation model. The main uncertainty is found to be the inaccuracy of the decay energy predictions.