Nuclear resonance fluorescence scattering has been observed to measure the lifetimes of the first excited states in ~SNa (0.440 MeV), 24Mg (1.368 M~V), 2sSi (1.772 MeV), and alp (1.265 MeV). Inelastic proton scattering at energies between 1.8 and 3.2 MeV in solid targets served as a Doppler-broadened gamma source. The intensity of resonant gamma rays, which strongly depends on the energy loss of the excited recoils in the target, was calculated using average nuclear and electronic stopping powers of Lindhard and Scharff for heavy nuclear particles. The resonance scattering experiments yielded for ZSNa (0.440 MeV) : t m = 1.62-[-0.10 psec, 24Mg (1.368 MeV) : t m = 1.95-t-0.26 psec, 2aSi (1.772 MeV) : t m = 0.71-t-0.10 psec, sxp (1.265 MeV) : t m = 0.74-t-0.10 psec. These results are in excellent agreement with other data on the different lifetimes. In addition they confirm the Lindhard theory of nuclear stopping power to within at least 25 ~o in the energy region e = 10-3--10 -x, where range measurements become difficult. The method of evaluating NRF scattering experiments with solid sources in the 0.01-10 psec lifetime region is described in detail.
NUCLEAR REACTIONS "Na, 24Mg, "Si, 3tP(7,, ?), E = 0.440, 1.368, 1.772, 1.265 MeV; measured ~7.
Deduced level Tยฝ, dE/d.x for heavy nuclei. Enriched 24Mg target.