  The intrinsic decay rate of orthopositronium formed in ${\rm SiO_2}$ powder
is measured using the direct $2\gamma$ correction method such that the time
dependence of the pick-off annihilation rate is precisely determined using high
energy-resolution germanium detectors. As a systematic test, two different
types of ${\rm SiO_2}$ powder are used with consistent findings. The intrinsic
decay rate of orthopositronium is found to be $7.0396\pm0.0012 (stat.)\pm0.0011
(sys.)\mu s^{-1}$, which is consistent with previous measurements using ${\rm
SiO_2}$ powder with about twice the accuracy. Results agree well with a recent
$O(\alpha^2)$ QED prediction, varying $3.8-5.6$ experimental standard
deviations from other measurements.
