MEAN LIVES OF POSITRONS IN ALUMINUM AND THE ALKALI METALS

Abstract

The time distribution of positron annihilations in the metals aluminum, lithium, sodium, potassium, and cesium have been measured with a fast time-to-amplitude converter. The decay curves appear to be complex, with about 5% of the events having a mean life of approximately 5×10⁻¹⁰ sec. The main (95%) components of the decay curves show the following mean lives, in units of 10⁻¹⁰ sec: Al, 1.9 ± 0.2; Li, 2.9 ± 0.2; Na, 3.15 ± 0.2; K, 4.0 ± 0.2; Cs, 4.3 ± 0.2. The results for the alkali metals disagree with the previously published measurements of De Benedetti and Richings (1952). These results are discussed, and the lifetimes for other metals are predicted roughly from them and from the angular correlation measurements of other workers.