Whereas the 7.2 min ${}^{240}\mathrm{Np}$, first identified over 60 years ago, has been assigned conflicting configuration by various investigators, the 62 min ${}^{240}\mathrm{Np}$ is assigned a “probable” configuration, deduced in each case by primarily focusing on just a single $\beta$-connected pair of levels in either ${}^{240}\mathrm{Np}$ (${\beta }^{-}$) ${}^{240}$Pu or ${}^{240}$U (${\beta }^{-}$) ${}^{240}\mathrm{Np}$ decay. We evaluate the level energies of physically admissible 2qp configurations in ${}_{93}^{240}$Np${}_{147}$ employing a three-step procedure, with experimental inputs at each step, and using a well tested two-particle rotor model with inclusion of residual $n$-$p$ interaction and other contributions. This exercise clearly establishes that the 62 min ${}^{240}\mathrm{Np}$ and the 7.2 min ${}^{240}\mathrm{Np}$ isomers constitute a Gallagher-Moszkowski (GM) doublet corresponding to the two-quasiparticle (2qp) configuration $5^{+}\{p5/2^{+}\left[642\right]\pm n5/2^{+}\left[622\right]\}{0}^{+}$ with $J^{\pi }\mathit{K}=1^{+}0$ for the higher-lying 7.2 min isomer. This assignment is conclusively confirmed in a level-by-level analysis of data on 23 $\beta$ transitions in these decays. Structures of a few other ${}^{240}\mathrm{Np}$ levels populated in ${}^{240}$U $\beta$ decay are also discussed.

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