$\gamma$ and conversion-electron spectra of mass-separated ${}_{}{}^{241}{}_{}{}^{}\mathrm{Cm}$ (32.8 day) samples were measured at high resolution with Ge(Li) detectors and a magnetic $\beta$-ray spectrometer; 28 $\gamma$ rays and 76 conversion lines were identified. The multipolarities of most of the 28 transitions in ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$ were deduced. Two-parameter $\gamma -\gamma$ coincidences confirmed a level scheme incorporating all transitions in six rotational bands. The observed half-life of ${}_{}{}^{241}{}_{}{}^{}\mathrm{Cm}$ via the decay of the 471.8 keV $\gamma$ ray was 32.8 ± 0.2 day. The $\alpha$ branching deduced from the measurements of $L_2$ and $L_3$ electron lines of the 145.5 keV transition in ${}_{}{}^{237}{}_{}{}^{}\mathrm{Pu}$ was (1.0 ± 0.1)%. The $\alpha$ singles spectrum of ${}_{}{}^{245}{}_{}{}^{}\mathrm{Bk}$ (5 day) decay to ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$ showed 12 $\alpha$ groups feeding the 3 lowest bands. On the basis of these measurements six single-particle states in ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$ have been identified. The ground state of ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$ is known to be $\frac{5}{2}-\left[523\right]\mathrm{}$. The following Nilsson band-head assignments have been made: (keV, $K\pi \left[N{n}_z\Lambda \right]$: 205.9, $\frac{5}{2}+\left[642\right]\mathrm{}$; $\frac{3}{2}-\left[521\right]\mathrm{}$; $623.1,\frac{1}{2}+\left[400\right]\mathrm{}$; 652.1, $\frac{1}{2}-\left[530\right]\mathrm{}$; and 670.2, $\frac{3}{2}+\left[651\right]\mathrm{}$. The 266.0 keV $E1\mathrm{}$ transition $\frac{3}{2}-\left[521\right]\mathrm{}\to \frac{5}{2}+\left[642\right]\mathrm{}$) was found to have the most highly anomalous conversion coefficients yet observed, with anomaly factors of 100-200, consistent with $E1\mathrm{}$ penetration conversion parameter sets ${\lambda }_1,{\lambda }_2$ = (18.5,283) or (-19.3, -63); the exiting 205.9 keV $E1\mathrm{}$ transition ($\frac{5}{2}+\left[642\right]\mathrm{}\to \frac{5}{2}-\left[523\right]\mathrm{}$) shows normal $E1\mathrm{}$ conversion. The 471.8 keV $M1+\sim 7\% E2\mathrm{}$ transition $\frac{3}{2}-\left[521\right]\mathrm{}\to \frac{5}{2}-\left[523\right]\mathrm{}$ also shows anomalous (factor of 3) conversion, with an $M1\mathrm{}$ penetration parameter ∼5.5. There is some indication of anomalously low $K$ conversion for transitions near $K$ threshold. Observed $P_1$ conversion line intensities are about twice the theoretical $P_1$ conversion coefficient predictions. Seven $\mathrm{KLL}$- and two $\mathrm{KLM}$ - Auger electron lines were observed and the $K$-shell fluorescent yield was deduced as (96.5 ± 0.4)%.

RADIOACTIVITY ${}_{}{}^{241}{}_{}{}^{}\mathrm{Cm}$ [from ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}(\alpha ,2n)$]; measured $T_{\frac{1}{2}}$, $E_{\gamma }$, $I_{\gamma }$, $X_K$, ${\omega }_K$, $E_{\mathrm{ce}}$, $I_{\mathrm{ce}}$, $e_{\mathrm{AKLL}}$, anomalous $E1\mathrm{}$ and $M1\mathrm{}$ conversions, deduced penetration parameters and retardation, deduced ${\alpha }_{P_1}$, $\gamma \gamma$-coin, $\alpha$ branching, ${}_{}{}^{245}{}_{}{}^{}\mathrm{Bk}$ [from ${}_{}{}^{244}{}_{}{}^{}\mathrm{Cm}(\alpha ,p2n)$; measured $E_{\alpha }$, $I_{\alpha }$; deduced hindrance factors. ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$ deduced levels, $log\mathrm{ft}$ (EC), $\gamma$ multipolarity, $I$, $\pi$, 6 single-particle states. Mass-separated ${}_{}{}^{241}{}_{}{}^{}\mathrm{Cm}$. Toroidal $\beta$ spectrometer at 0.05% FWHM.

• Received 6 May 1974

DOI:https://doi.org/10.1103/PhysRevC.10.803