  In this talk we consider the O(alpha_s) radiative corrections to the decay of
an unpolarized top quark into a bottom quark and a W gauge boson where the
helicities of the W are specified as transverse-plus, transverse-minus and
longitudinal. The O(alpha_s) radiative corrections lower the normalized
longitudinal rate Gamma_L/Gamma by 0.8%. We find that the normalized
transverse-plus rate Gamma_+/Gamma, which vanishes at the Born term level for
m_b->0, receives radiative correction contributions at the sub-percent level.
Our results are discussed in the light of recent measurements of the helicity
content of the W in top quark decays by the CDF Collaboration.
