  A quantum mechanical analysis of the bremsstrahlung in $\alpha$ decay of
$^{210}$Po is performed in close reference to a semiclassical theory. We
clarify the contribution from the tunneling, mixed, outside barrier regions and
from the wall of the inner potential well to the final spectral distribution,
and discuss their interplay. We also comment on the validity of semiclassical
calculations, and the possibility to eliminate the ambiguity in the nuclear
potential between the alpha particle and daughter nucleus using the
bremsstrahlung spectrum.
