Energy levels of Bk 249 populated in the α decay of 99 253 Es and β − decay of 96 249 Cm

The level structure of $^{249}\mathrm{Bk}$ has been investigated by measuring the \ensuremath{\gamma}-ray spectra of an extremely pure $^{253}\mathrm{Es}$ sample obtained by milking this nuclide from $^{253}\mathrm{Cf}$ source material produced in the High Flux Isotope Reactor at Oak Ridge National Laboratory. Additional information on the $^{249}\mathrm{Bk}$ levels was obtained from the ${\ensuremath{\beta}}^{\ensuremath{-}}$-decay study of $^{249}\mathrm{Cm}$, produced by neutron irradiation of $^{248}\mathrm{Cm}$. Using the results of the present study together with the data from previous $^{248}\mathrm{Cm}$($\ensuremath{\alpha},t$) and $^{248}\mathrm{Cm}$($^{3}\mathrm{He},d$) reactions, the following single-particle states have been identified in $^{249}\mathrm{Bk}$: 7/2${}^{+}$[633], 0.0 keV; 3/2${}^{\ensuremath{-}}$[521], 8.78 keV; 1/2${}^{+}$[400], 377.55 keV; 5/2${}^{+}$[642], 389.17 keV; 1/2${}^{\ensuremath{-}}$[530], 569.20 keV; 1/2${}^{\ensuremath{-}}$[521], 643.0 keV; 5/2${}^{\ensuremath{-}}$[523], 672.9 keV; and 9/2${}^{+}$[624], 1075.1 keV. Four vibrational bands were identified at 767.9, 932.2, 1150.7, and 1223.0 keV with tentative assignments of {7/2${}^{+}$ [633] $\ensuremath{\bigotimes}{1}^{\ensuremath{-}}$}9/2${}^{\ensuremath{-}}$, {7/2${}^{+}$ [633] $\ensuremath{\bigotimes} {0}^{\ensuremath{-}}$}7/2${}^{\ensuremath{-}}$, {7/2${}^{+}$ [633] $\ensuremath{\bigotimes} {1}^{\ensuremath{-}}$}5/2${}^{\ensuremath{-}}$, and {7/2${}^{+}$ [633] $\ensuremath{\bigotimes} {0}^{+}$}7/2${}^{+}$, respectively. A band at 899.9 keV was observed in $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence measurements and given a tentative spin assignment of 3/2. It is possibly associated with a 2${}^{\ensuremath{-}}$ phonon coupled to the ground state, with configuration {7/2${}^{+}$ [633] $\ensuremath{\bigotimes} {2}^{\ensuremath{-}}$}3/2${}^{\ensuremath{-}}$. Three levels at 624.3, 703.5, and 769.1 keV were assigned spins of 5/2, 7/2, and 9/2, respectively. These could be the members of the 3/2${}^{+}$ [651] band, expected in this energy region.