The decay of neutron-rich niobium isotopes in the mass region $A\simeq 100$ has been investigated by $\gamma$-ray singles and $\gamma$-$\gamma$ coincidence measurements. The isotopes were produced by thermal-neutron induced fission of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$, and ${}_{}{}^{249}{}_{}{}^{}\mathrm{Cf}$, and niobium was separated from fission-product mixtures with an automated chemical procedure. Isomerism was found in the even-mass niobium isotopes with the following half-lives: 1.5 and 3.1 sec for ${}_{}{}^{100}{}_{}{}^{}\mathrm{Nb}$, 1.3 and 4.3 sec for ${}_{}{}^{102}{}_{}{}^{}\mathrm{Nb}$, and 0.8 and 4.8 sec for ${}_{}{}^{104}{}_{}{}^{}\mathrm{Nb}$. Half-lives and $\gamma$ rays were assigned to the 15.0-sec ${}_{}{}^{99}{}_{}{}^{}\mathrm{Nb}$, 7.1-sec ${}_{}{}^{101}{}_{}{}^{}\mathrm{Nb}$, 1.5-sec ${}_{}{}^{103}{}_{}{}^{}\mathrm{Nb}$, and ∼1-sec ${}_{}{}^{106}{}_{}{}^{}\mathrm{Nb}$. Revised half-life values are given for the 7.1-sec ${}_{}{}^{100}{}_{}{}^{}\mathrm{Zr}$ and 2.9-sec ${}_{}{}^{102}{}_{}{}^{}\mathrm{Zr}$. RADIOACTIVITY ${}_{}{}^{99,100,101,102,103,104,106}{}_{}{}^{}\mathrm{Nb}$, ${}_{}{}^{100,102}{}_{}{}^{}\mathrm{Zr}$; measured $T_{\frac{1}{2}}$, $E_{\gamma }$, $\gamma$-$\gamma$-coin. ${}_{}{}^{100,102,104}{}_{}{}^{}\mathrm{Mo}$ deduced levels. Fission ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$, ${}_{}{}^{249}{}_{}{}^{}\mathrm{Cf}(n_{\mathrm{th}},f)$; automated chemical separation procedure, Ge(Li) detectors.

• Received 30 June 1975

DOI:https://doi.org/10.1103/PhysRevC.14.211