Measurement of  -Transition Lifetimes by Recoil Methods

Methods of utilizing the recoil motion of excited nuclei produced in disintegrations, to obtain estimates of the half-lives of excited states, are described. They involve measurement either of the distance moved by the recoiling nucleus before radiation occurs, or of the small Doppler shift in frequency produced by the recoil motion. Details are given of the application of some of the methods to the measurement of the half-lives of the levels of 16 O at 6.13 MeV (E3 transition), 6.9 MeV (E2) and 7.1 MeV (E1), with the following results: 6.13 MeV, 5 × 10 -12 less, similar τ less, similar 10 -11 sec; 6.9 MeV, τ less, similar 1.2 × 10 -14 sec; 7.1 MeV, τ less, similar 8 × 10 -15 second.