  The Oslo Method has been applied to particle-$\gamma$ coincidences following
the $^{239}\mathrm{Pu}$(d,p) reaction to obtain the nuclear level density (NLD)
and $\gamma$-ray strength function ($\gamma$SF) of $^{240}\mathrm{Pu}$. The
experiment was conducted with a 12 MeV deuteron beam at the Oslo Cyclotron
Laboratory. The low spin transfer of this reaction leads to a spin-parity
mismatch between populated and intrinsic levels. This is a challenge for the
Oslo Method as it can have a significant impact on the extracted NLD and
$\gamma$SF. We have developed an iterative approach to ensure consistent
results even for cases with a large spin-parity mismatch, in which we couple
Green's Function Transfer calculations of the spin-parity dependent population
cross-section to the nuclear decay code RAINIER. The resulting $\gamma$SF shows
a pronounced enhancement between 2-4 MeV that is consistent with the location
of the low-energy orbital $M1$ scissors mode.
