Short-Lived Isomers of Nuclei

A search for short-lived nuclear isomers of half-lives between ${10}^{-6\mathrm{}}$ and ${10}^{-3\mathrm{}}$ sec. has been performed using the method of delayed coincidences between two Geiger counters. A short-lived isomer is detected by the measurement of the time lapsed between $\beta$-decay and $\gamma$- (or internal conversion electron) emission. Out of 60 nuclei investigated, 4 short-lived isomeric states were found. These are: ${\mathrm{Ta}}^{181*}$ (22 μsec.), ${\mathrm{Re}}^{187*}$ (0.65 μsec.), ${\mathrm{Tm}}^{169*}$ (1 μsec.), and ${\mathrm{Tm}}^{171*}$ (2.5 μsec.).