Am243αDecay: Multipolarity ofγTransitions

Conversion coefficients and probable multipolarities were measured for seven $\gamma$ rays from levels of ${}_{}{}^{239}{}_{}{}^{}\mathrm{Np}$ populated by the $\alpha$ decay of ${}_{}{}^{243}{}_{}{}^{}\mathrm{Am}$. The $\gamma$ energies in keV and their multipolarities are 43.1 keV ($M1+E2\mathrm{}$), 55.4 keV ($M1+E2\mathrm{}$), 74.7 keV ($E1\mathrm{}$), 86.7 keV ($E1\mathrm{}$), 98.5 keV ($E2\mathrm{}$), 117.8 keV ($E1\mathrm{}$), and 142.0 keV ($E1\mathrm{}$). The multipolarities of the 74.7- and 117.8-keV $\gamma \text{'}\mathrm{s}$ have been previously reported. The 98.5-keV transition was seen only in $e^{-}$ spectra and has not been noted before. These multipolarities are in agreement with level-spin assignments. Gamma branching ratios from the 74.7-, 117.8-, and 173.2-keV levels have been calculated. Coincidences with $\alpha \text{'}\mathrm{s}$ were required in order to eliminate radiations from the ${\beta }^{-}$ decay of the ${}_{}{}^{239}{}_{}{}^{}\mathrm{Np}$ daughter. The 100-${\mathrm{mm}}^2$×3-mm-deep Si(Li) detector gave an $e^{-}$ resolution of 2.0 keV over the energy range studied. Both the detector and the field-effect transistor input stage were cooled to -150°C.