  A generalized method to calculate the excitation-energy dependent parity
ratio in the nuclear level density is presented, using the assumption of
Poisson distributed independent quasi particles combined with BCS occupation
numbers. It is found that it is crucial to employ a sufficiently large model
space to allow excitations both from low-lying shells and to higher shells
beyond a single major shell. Parity ratios are only found to equilibrate above
at least 5-10 MeV of excitation energy. Furthermore, an overshooting effect
close to major shells is found where the parity opposite to the ground state
parity may dominate across a range of several MeV before the parity ratio
finally equilibrates. The method is suited for large-scale calculations as
needed, for example, in astrophysical applications. Parity distributions were
computed for all nuclei from the proton dripline to the neutron dripline and
from Ne up to Bi. These results were then used to recalculate astrophysical
reaction rates in a Hauser-Feshbach statistical model. Although certain
transitions can be considerably enhanced or suppressed, the impact on
astrophysically relevant reactions remains limited, mainly due to the thermal
population of target states in stellar reaction rates.
