  Effects of difference in the spin and parity distributions for the surrogate
and neutron-induced reactions are investigated. Without assuming specific
(schematic) spin-parity distributions, it was found that the surrogate ratio
method can be employed to determine neutron fission and capture cross sections
if 1) weak Weisskopf-Ewing condition (defined in this paper) is satisfied, 2)
there exist two surrogate reactions whose spin-parity distributions of the
decaying nuclei are almost equivalent, and 3) difference of the representative
spin values between the neutron-induced and surrogate reactions is no much
larger than 10 $\hbar$. If these conditions are satisfied, we need not to know
the spin-parity distributions populated by the surrogate method. Instead, we
should just select a pair of surrogate reactions which will populate the
similar spin-parity distributions, using targets having similar structure and
reactions having the similar reaction mechanisms. Achievable accuracy is
estimated to be around 5 and 10 % for fission and capture channels,
respectively, for nuclei of the Uranium region. The surrogate absolute method,
on the contrary, can be marginally applicable to determination of fission cross
sections. However, there will be little hope to apply this method for capture
cross section measurements unless the spin-parity distributions in the
neutron-induced and surrogate reactions are fairly close to each other or the
difference can be corrected theoretically. The surrogate ratio method was shown
also to be a robust method in the presence of breakup reactions, again, without
assuming specific breakup reaction mechanisms.
