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With use of the new half-life for 32 Si, earlier experiments 7 " 10 based on assumed nuclear-production rates can be viewed as cross-section measurements, and the polar-ice study 2 can be viewed as a cosmic-ray-flux measurement. Knowledge of a more reliable half-life should stimulate more studies like these as well as studies of 32 Si in groundwater and meteorites. The lower half-life gives 32 Si special importance in meteorites since it now falls between ^Ti (t 1/2 = 47 yr) and 39 Ar (t 1/2 = 269 yr). For these three isotopes target effects largely cancel since all are produced by iron spallation; therefore their ratios could provide important information on the galactic cosmic-ray flux over the last few hundred years.We thank K. Sakamoto for providing the 32 Si sample and R. P. Beukens and the rest of our colleagues at the University of Toronto for useful discussions.

The lifetime and y-ray branching of the 3.90-MeV (2 ) state of Ca have been measured using the reactions Ca4 (p, p')Ca at a bombarding energy of 7.32 MeV and K39(p, y)Ca4 at the E& =1.344-MeV resonance. Consistent values for the lifetime were obtained from the Doppler shifts of the 3.90-MeV p rays in both reactions and from the 0' line shape in the K (p, y)Ca reaction. A value of v' =50 +5 fsec is adopted for the mean lifetime of the 3.90-MeV state. The 3.90 3.35-MeV branching ratio was measured by observing the 0.555-MeV cascade y rays in quadruple coincidence with the two annihilationp rays and the inelastic protons in the Ca (p, p')Ca reaction, or in triple coincidence with annihilation y rays in the K~-(p, y)Ca reaction. Results are in agreement and the adopted branch is (7.95 +0.8) &&10 By combining the lifetime and branching results, the 0.555-MeV E2 transition rate corresponds to s. B(5'2; 3.90 (2+) -3.35 (0+)) of 250 +35 et fm . This result is in excellent agreement with recent theoretical estimates of the transition strength. The mean lifetime of the 5.28-MeV (4 ) state of Ca was measured to be 310+60 fsec. The corresponding B(E2; 5.28 (4+) 3.90 (2+1)) of 535 +110 e fm4 is in reasonable agreement with expectations based on a strong-deformation rotational model of the states.