  We report the first ever measurements of the thermalization length of
low-energy electrons injected into solid para-hydrogen at a temperature
\(T\approx 2.8\,\)K. The use of the pulsed Townsend photoinjection technique
has allowed us to investigate the behavior of quasi-free electrons rather than
of massive, slow negative charges as reported in all previous literature. We
have found an average thermalization length \(\langle z_0\rangle\approx
260\,\)\AA\ which is 3 to 5 times longer than that in liquid helium at the same
temperature.
