Alpha Decay ofAm243

The decay of ${}_{}{}^{243}{}_{}{}^{}\mathrm{Am}$ has been studied by observing $\alpha -\gamma$ coincidences using Si(Au) surface-barrier and Ge(Li) detectors in conjunction with a 4096-channel two-parameter analyzer. $\gamma$ rays of 31.2, 43.6, 50.6, 55.4, 74.8, 86.7, 117.8, 142.0, 169, 195, and 220 keV were observed. only the 43.6-, 74.8-, and 117.8-keV $\gamma$ rays have been previously reported. These results confirm many features of the previously accepted level scheme of the ${}_{}{}^{239}{}_{}{}^{}\mathrm{Np}$ daughter. Furthermore, new levels at 72 and 123 keV have been found which are apparently the $\frac{9}{2}+$ and $\frac{11}{2}+$ members, respectively, of the ground-state rotational band. These energies agree well with predictions based on the collective model. The intensity ratio of $\alpha$ groups to the ground and first excited states has been measured to be 1.17, in poor agreement with a theoretical estimate of 2.03.