Lifetimes of gamma-ray transitions by delayed-coincidence measurements

An apparatus for the measurement of the lifetimes of gamma-ray transitions between nuclear excited states has been designed and constructed. With this apparatus, lifetimes as short as 1.5 x 10⁻¹⁰ seconds may be determined. This lower limit is shown to be inherent in the scintillation detectors available and not in the electronic circuits which are themselves capable of much better performance. Measurements have been carried out on several radioactive nuclei and have yielded the following results: (1) The two excited states of Ni⁶⁰ have half-lives less than 1.6 x 10⁻¹⁰ seconds. (2) The three excited states of Co⁵⁹ have half-lives less than 2 x 10⁻¹⁰ seconds. (3) No detectable half-life is found in the decay of Eu¹⁵²,¹⁵⁴. (4) An excited state with a half-life of 1.1 x 10⁻⁹ seconds is present in W¹⁸². We identify this transition as magnetic quadrupole. (5) A half-life.of 2.3 x 10⁻¹⁰ seconds is found for the .607 Mev transition in Te¹²⁴ which has previously been classified as electric quadrupole.Science, Faculty ofPhysics and Astronomy, Department ofGraduat