Precision Doppler-shift attenuation lifetime measurements in28Si and31P

Abstract
The mean lives of three excited states have been measured by bombarding an implanted 4He target with a 28Si beam and observing the (particle coincident) gamma -ray line-shapes at 0 degrees . The results are: (in 28Si) 1778 keV level, tau m=697+or-39 fs; (in 31P) 1266 keV level, tau m=761+or-47 fs, 2234 keV level, tau m=391+or-25 fs. The last lifetime is of interest in attempts to calibrate the Doppler-shift attenuation method at low initial recoil velocities.