The radiations of ${\mathrm{U}}^{240}$ and 7.3-min ${\mathrm{Np}}^{240}$ have been studied with a solenoidal beta spectrometer, beta-and gamma-scintillation spectrometers, and 180° permanent-magnet spectrographs. The principal decay branch of ${\mathrm{U}}^{240}$ is a 0.36-Mev beta transition to the 7.3-min state of ${\mathrm{Np}}^{240}$. The only other radiations observed which are attributed to ${\mathrm{U}}^{240}$ are the conversion lines associated with a 0.044-Mev transition.

The decay scheme of 7.3-min ${\mathrm{Np}}^{240}$ is considerably more complicated than that indicated by previous investigations. On the basis of coincidence studies, intensity data, internal conversion coefficients, and the measured transition energies, a consistent level scheme for ${\mathrm{Pu}}^{240}$ is proposed which has excited states at 0.043, 0.142, 0.597, 0.858, 0.900, 0.942, 1.42, 1.53, and 1.62 Mev. The ground-state transition from the 0.858-Mev level is of $E0\mathrm{}$ multipolarity, identifying this level as a 0+ state. There are beta transitions to the ground state of ${\mathrm{Pu}}^{240}$ ($Q_{\beta }=2.18\mathrm{}$ Mev) and to each of the above excited states except the one at 0.142 Mev. Consideration of the beta-decay information leads to a spin and parity assignment of 1+ for 7.3-min ${\mathrm{Np}}^{240}$. Various features of the decay scheme are compared with the predictions of current models of nuclear structure.

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