  Ferromagnetic half-metal Co$_2$CrAl films and tunnel contacts Co$_2$CrAl -
insulator (I) - Pb are fabricated and investigated. It is found that the
normalized differential conductivity $\sigma ^{\rm FS} $ of such tunnel
junctions with low resistance is larger than the normalized differential
conductivity $\sigma ^{\rm NS} $ of known normal metal - I - superconductor
type tunnel junctions. It is shown that the observed increase in $\sigma ^{\rm
FS} $ is caused by the accumulation of spin polarized electrons in a
superconductor and can be used for estimating the spin polarization degree $P$
in ferromagnets. This method shows that $P$ of L2$_1$-type ordered Co$_2$CrAl
Heusler alloy films at $T = 4.2{\rm K}$ is close to 1.
