  The intrinsic decay rate of orthopositronium (o-Ps) formed in SiO_2 powder
was measured using a modified method which determined the time dependence of
the pick-off annihilation rate using high-energy-resolution germanium
detectors. That is, the main systematic error due to thermalization was
accounted for and integrated into the time spectrum fitting procedure. The
averaged value was found to be lambda_(o-Ps)=7.0399+0.0020-0.0021(stat.)
+-0.0015(sys.) mu s^{-1}, which agrees well with the O(alpha^2) QED prediction;
varying 2.8-4.2 experimental standard deviations from other measurements.
