In order to determine the dependence of the probability of decay on momentum, mesotrons with range between 196 and 311 g/${\mathrm{cm}}^2$ of lead and mesotrons with range larger than 311 g/${\mathrm{cm}}^2$ of lead were investigated separately. The softer group of mesotrons was found to disintegrate at a rate about three times faster than the more penetrating group, in agreement with the theoretical predictions based on the relativity change in rate of a moving clock. A new value of the proper lifetime of mesotrons of (2.4±0.3)×${10}^{-6\mathrm{}}$ sec. is determined, based upon measurements with particles with momentum of approximately 5×${10}^8$ ev/c.

• Received 13 December 1940

DOI:https://doi.org/10.1103/PhysRev.59.223