Quantitative technetium and niobium abundances in heavy-element stars

We have used the lambda5924 intercombination line of Tc I to derive Tc abundances in R CMi and CY Cyg and upper limits in two additional stars. In addition we have derived abundances of, V, Zr, Nb, Mo, and Ru relative to Ti in six stars. The ratios of Tc/Mo indicate that very little decay of Tc has taken place since the last neutron exposure, which must have occurred less than 4 x 105 years ago. The abundance of Nb indicates that nearly complete decay of 93Zr has taken place, which requires a time scale of several times 106 years. We interpret this as indicating that multiple neutron capture events, probably shell flashes, have occurred and the Nb produced by the decay of 93Zr has been convected out of the shell flashing region and thus has been protected from neutron capture during the most recent flashes which produced the observed Tc