  Absolute measurements were conducted to study the bremsstrahlung emission
from ~5-25 keV electrons incident on three thick solid conductive compounds of
MoSi$_2$, TiB$_2$ and ZrB$_2$. The additivity approximation was applied in the
Monte Carlo PENELOPE simulations for compounds and mixtures. The results showed
that in general the experimental bremsstrahlung spectra were in good agreement
with the Monte Carlo simulation results, suggesting the feasibility of the
additivity approximation in Monte Carlo simulations for the studied cases even
in the absolute measurements and that the significant differences between
experiments and Monte Carlo simulations near the Duane-Hunt limit for
insulating targets in previous studies do not appear in the present studies.
