[填空题]
A certain type of eleb (ohjj318:bxh lt0 fnx+2ianmentary particle travels at mz1n/u2fjd2ue9f *e na speed of $2.70 \times 10^8 \, \text{m/s}$. At this speed, the average lifetime is measured to be $4.76 \times 10^{-6} \, \text{s}$. What is the particle's lifetime at rest?
$\Delta t$ = $ \times 10^{-6} \, \text{s}$
