Lifetime of the 6.880-MeV Level ofSi28

The Doppler-broadened 6.91-MeV radiation from the ${\mathrm{F}}^{19}(p, \alpha \gamma ){\mathrm{O}}^{16}$ reaction has been used to resonantly excite the 6.880-MeV Level of ${\mathrm{Si}}^{28}$. The angular distribution of the scattered radiation is consistent only with a spin of 2. Since the resonance absorption is small, the lifetime was determined from the scattering results. A Li-drifted germanium detector was used to observe the incident spectral shape and from this the number of 6.880-MeV gamma rays per unit energy interval incident on the scatterer was determined. Assuming the ground-state branching to be between 70% and 90%, the mean life obtained is $1.93\times {10}^{-13\mathrm{}} sec<\tau <2.48\mathrm{}\times {10}^{-13\mathrm{}} sec$.