The nuclides ${}_{}{}^{242}{}_{}{}^{}\mathrm{U}$ and ${}_{}{}^{242}{}_{}{}^{}\mathrm{Np}$ were discovered by chemical separations from targets of ${}_{}{}^{244}{}_{}{}^{}\mathrm{Pu}$ irradiated with 30-160 MeV neutrons followed by $\gamma$-ray and $\beta$-ray spectroscopy. The parent ${}_{}{}^{242}{}_{}{}^{}\mathrm{U}$ decays with $T_{\frac{1}{2}}=16.8\mathrm{}\pm 0.5$ min; 14 $\gamma$ rays ranging from 55.6 keV to 585.0 keV were assigned to its decay. The ${}_{}{}^{242}{}_{}{}^{}\mathrm{Np}$ daughter half-life is 2.2±0.2 min and 39 $\gamma$ rays following its decay have energies between 620.6 and 2370.5 keV. $Q_{{\beta }^{-}}$ of ${}_{}{}^{242}{}_{}{}^{}\mathrm{Np}$ is 2.7±0.2 MeV. A level scheme is proposed for ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$ in which the lowest 7 levels were previously described and 12 new levels are shown. The ground state of ${}_{}{}^{242}{}_{}{}^{}\mathrm{Np}$ is assigned $I^{\pi }=1^{+} \mathrm{and} 6$ excited levels are proposed which accommodate most of the observed $\gamma$ rays from decay of ${}_{}{}^{242}{}_{}{}^{}\mathrm{U}$.

RADIOACTIVITY ${}_{}{}^{242}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{242}{}_{}{}^{}\mathrm{Np}$ from ${}_{}{}^{244}{}_{}{}^{}\mathrm{Pu}(n, 2pn){}_{}{}^{242}{}_{}{}^{}\mathrm{U}\stackrel{{\beta }^{-}}{\to }{}_{}{}^{242}{}_{}{}^{}\mathrm{Np}$; radiochemistry, Ge(Li) and plastic detectors. ${}_{}{}^{242}{}_{}{}^{}\mathrm{U}$: measured $T_{\frac{1}{2}}$, $E_{\gamma }$, $I_{\gamma }$; deduced $E_{{\beta }^{-}}$, $I_{{\beta }^{-}}$, $log\mathrm{ft}$, decay scheme, $J$, $\pi$, Nilsson state assignments. ${}_{}{}^{242}{}_{}{}^{}\mathrm{Np}$: measured $T_{\frac{1}{2}}$, $E_{\gamma }$, $I_{\gamma }$, $E_{{\beta }^{-}}$, $I_{{\beta }^{-}}$; deduced $log\mathrm{ft}$, decay scheme, $J$, $\pi$, Nilsson assignments.

• Received 9 January 1979

DOI:https://doi.org/10.1103/PhysRevC.19.2332