  An influence of a magnetic field on beta-processes is investigated under
conditions of a core-collapse supernova. For realistic magnetic fields
reachable in astrophysical objects we obtain simple analytical expressions for
reaction rates of beta-processes as well as the energy and momentum transferred
from neutrinos and antineutrinos to the matter. Based on the results of
one-dimensional simulations of a supernova explosion, we found that, in the
magnetic field with the strength $B \sim 10^{15}$ G, the quantities considered
are modified by a few percents only and, as a consequence, the magnetic-field
effects can be safely neglected, considering neutrino interaction and
propagation in a supernova matter. The analytical results can be also applied
for accretion discs formed at a merger of compact objects in close binary
systems.
