Lifetime of Positrons in Superconducting Lead

Comparison of the mean lifetime of positrons in lead at 4.2°K with that at 10°K indicates (a), no change greater than 2×${10}^{-10\mathrm{}}$ sec in the short-lived component, and (b), no more than 0.3% abundance of a component with lifetime greater than 2×${10}^{-9\mathrm{}}$ sec.