Electron-Capture Decay ofPu237

The conversion and $K$-Auger electron spectra of ${\mathrm{Pu}}^{237}$ (produced by alpha bombardment of ${\mathrm{U}}^{235}$) were examined with a permanent-magnet spectrograph and a solenoidal beta-ray spectrometer. The photon spectrum was studied with scintillation spectrometers and the following intensity ratios were determined: $K$ x-radiation: $L$ x-radiation: 59.6-kev gamma radiation = 1.00: 0.75: 0.14. Data from the beta-ray and scintillation spectrometers were used to calculate a $K$-Auger electron coefficient of 0.06±0.01 for $Z=93\mathrm{}$. Coincidence measurements established the existence of both $K$- and $L$-electron capture to the 59.6-kev level of ${\mathrm{Np}}^{237}$. The ratio of $L$ to $K$ capture to that level was found to be 2.8, and from this ratio a total electron-capture decay energy of 0.21 Mev was calculated for ${\mathrm{Pu}}^{237}$. This value is in good agreement with that of 0.22 Mev estimated from closed decay-energy cycles. The experimental data indicate that the principal branches of electron-capture decay are to the 59.6-kev (15%) and the 33.2-kev (22%) levels, and to the ground state (60%) of ${\mathrm{Np}}^{237}$, with corresponding $log\mathrm{ft}$ values of 6.8, 6.9, and 6.8, respectively.