The general consequences of $T$ invariance for
the direct
and inverse binary reactions $a + b \rightarrow c + d$,
$c + d \rightarrow a + b$ with spin-1/2 particles $a$, $b$
and unpolarized particles $c$, $d$ are considered.
Using the formalism of helicity amplitudes, the polarization
effects are studied in the reaction $p + \,^{3}{He}
\rightarrow \pi^{+} + \,^{4}{He}$ and in the inverse process
$\pi^{+} + \,^{4}{He}\rightarrow p + \,^{3}{He}$. It is shown
that in the reaction $\pi^{+} + \,^{4}{He}
\rightarrow p + \,^{3}{He}$ the spins of the final proton and
$^{3}{He}$ nucleus are strongly correlated. A structural expression
through helicity amplitudes, corresponding to arbitrary emission
angles, is obtained for the correlation tensor. It is established
that in the reaction $\pi^{+} + \,^{4}{He} \rightarrow p +
\,^{3}{He}$ one of the "classical" incoherence inequalities of the
Bell type for diagonal components of the correlation tensor is
necessarily violated.