  The photoneutron reaction $^{181}\rm{Ta}(\gamma,3n)^{178m,g}\rm{Ta}$ was
investigated with the beam from the NSC KIPT electron linear accelerator
LUE-40. The measurements were performed using the residual $\gamma$-activity
method. The bremsstrahlung flux-averaged cross-sections
$\langle{\sigma(E_{\rm{\gamma max}})}\rangle$, $\langle{\sigma(E_{\rm{\gamma
max}})}\rangle_{\rm{m}}$, $\langle{\sigma(E_{\rm{\gamma
max}})}\rangle_{\rm{g}}$ and the isomeric ratio of the reaction products
$d(E_{\rm{\gamma max}})$ have been measured. Theoretical values of averaged
cross-sections and isomeric ratio were calculated using partial cross-sections
from the TALYS1.95 code for different level density models $LD$ 1-6. The
obtained experimental $d(E_{\rm{\gamma max}})$ agree with the literature data,
but differ from the theoretical values in absolute magnitude and the behavior
of the energy dependence. A comparison of the found averaged cross-sections
with the calculated ones showed the best agreement for the case of the $LD$ 5
model.
