Proton states, anomalous conversion, andK-Auger spectra inAm241fromCm241(electron capture) andBk245αdecays

Abstract

$\ensuremath{\gamma}$ 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 $\ensuremath{\beta}$-ray spectrometer; 28 $\ensuremath{\gamma}$ rays and 76 conversion lines were identified. The multipolarities of most of the 28 transitions in $^{241}\mathrm{Am}$ were deduced. Two-parameter $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ 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 $\ensuremath{\gamma}$ ray was 32.8 \ifmmode\pm\else\textpm\fi{} 0.2 day. The $\ensuremath{\alpha}$ 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 \ifmmode\pm\else\textpm\fi{} 0.1)%. The $\ensuremath{\alpha}$ singles spectrum of $^{245}\mathrm{Bk}$ (5 day) decay to $^{241}\mathrm{Am}$ showed 12 $\ensuremath{\alpha}$ 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 $\frac{5}{2}\ensuremath{-}[523]$. The following Nilsson band-head assignments have been made: (keV, $K\ensuremath{\pi}[N{n}_{z}\ensuremath{\Lambda}]$: 205.9, $\frac{5}{2}+[642]$; $\frac{3}{2}\ensuremath{-}[521]$; $623.1,\frac{1}{2}+[400]$; 652.1, $\frac{1}{2}\ensuremath{-}[530]$; and 670.2, $\frac{3}{2}+[651]$. The 266.0 keV $E1$ transition $\frac{3}{2}\ensuremath{-}[521]\ensuremath{\rightarrow}\frac{5}{2}+[642]$) was found to have the most highly anomalous conversion coefficients yet observed, with anomaly factors of 100-200, consistent with $E1$ penetration conversion parameter sets ${\ensuremath{\lambda}}_{1},{\ensuremath{\lambda}}_{2}$ = (18.5,283) or (-19.3, -63); the exiting 205.9 keV $E1$ transition ($\frac{5}{2}+[642]\ensuremath{\rightarrow}\frac{5}{2}\ensuremath{-}[523]$) shows normal $E1$ conversion. The 471.8 keV $M1+\ensuremath{\sim}7% E2$ transition $\frac{3}{2}\ensuremath{-}[521]\ensuremath{\rightarrow}\frac{5}{2}\ensuremath{-}[523]$ also shows anomalous (factor of 3) conversion, with an $M1$ penetration parameter \ensuremath{\sim}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 \ifmmode\pm\else\textpm\fi{} 0.4)%.RADIOACTIVITY $^{241}\mathrm{Cm}$ [from $^{239}\mathrm{Pu}(\ensuremath{\alpha},2n)$]; measured ${T}_{\frac{1}{2}}$, ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, ${X}_{K}$, ${\ensuremath{\omega}}_{K}$, ${E}_{\mathrm{ce}}$, ${I}_{\mathrm{ce}}$, ${e}_{\mathrm{AKLL}}$, anomalous $E1$ and $M1$ conversions, deduced penetration parameters and retardation, deduced ${\ensuremath{\alpha}}_{{P}_{1}}$, $\ensuremath{\gamma}\ensuremath{\gamma}$-coin, $\ensuremath{\alpha}$ branching, $^{245}\mathrm{Bk}$ [from $^{244}\mathrm{Cm}(\ensuremath{\alpha},p2n)$; measured ${E}_{\ensuremath{\alpha}}$, ${I}_{\ensuremath{\alpha}}$; deduced hindrance factors. $^{241}\mathrm{Am}$ deduced levels, $log\mathrm{ft}$ (EC), $\ensuremath{\gamma}$ multipolarity, $I$, $\ensuremath{\pi}$, 6 single-particle states. Mass-separated $^{241}\mathrm{Cm}$. Toroidal $\ensuremath{\beta}$ spectrometer at 0.05% FWHM.