Lifetimes of the First Excited States ofLi7andBe7

The lifetimes of the first excited states of ${\mathrm{Li}}^7$ and ${\mathrm{Be}}^7$ have been remeasured with the Doppler-shift attenuation method and a lithium-drifted germanium detector. The value of the mean life obtained for ${\mathrm{Li}}^7$*, (1.06±0.14)×${10}^{-13\mathrm{}}$ sec, is in better agreement with earlier measurements from resonance fluorescence than with previous determinations by the Doppler-shift method. The value obtained for ${\mathrm{Be}}^7$*, (1.92±0.25)×${10}^{-3\mathrm{}}$ sec, agrees with but is appreciably lower and more precise than an earlier Doppler-shift measurement. The value of 1.82±0.20 obtained for the ratio of the lifetimes, and the lifetimes themselves, are in excellent agreement with the range of values expected for intermediate coupling with $L-S$ coupling predominating ($\frac{a}{K}<3.6\mathrm{}$). They agree as well with specific theoretical predictions based on studies of $p$-shell nuclei.