Lifetimes of Potassium Doubletsλ4047−4andλ3447−6

Abstract

The lifetimes of the potassium doublets $\ensuremath{\lambda}4047\ensuremath{-}4$ and $\ensuremath{\lambda}3447\ensuremath{-}6$ were measured by the a.c. excitation method previously described. A sodium-hydride vacuum photocell of special design was used to measure the radiation from a potassium cell containing a hot cathode and two anodes. Measurements were made throughout a range of vapor pressures from 4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ mm to ${10}^{\ensuremath{-}2}$ mm. The lifetime of $\ensuremath{\lambda}4047\ensuremath{-}4$ was found to be 3.79\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ sec., the lifetime of $\ensuremath{\lambda}3447\ensuremath{-}6$ to be 8.50\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ sec., with an estimated precision of one percent. It was shown that the radiation emitted after electron excitation followed a simple exponential law. No change in the measured value of the lifetime was found for either of the doublets throughout the whole pressure range studied. This could be accounted for by the assumption that only 10 percent of the absorbed $\ensuremath{\lambda}4047\ensuremath{-}4$ is re-emitted at the same wave-length, and similarly for $\ensuremath{\lambda}3447\ensuremath{-}6$. Measurements made of the variation of the emission with pressure, and of the absorption, were consistent with this assumption.