2.0x105 250 1.5 200 1.0 150 100 0.5 50 0.0 0 2040 60 80 100 0 20 40 60 80 100 TIME (ns) TIME(ns) Fg.()A typical itid iftim vent captured by the sils.About 15sampes areolcted ithn the rise tme of the pulse. Thetimng noation isextracted from theitied pulses by oseation with a mode pue,the res of which is given n(b). The positron lifetme is then calculated as a timeifference between the peak postions