A high-efficiency cascade-photon-coincidence lifetime-measuring apparatus has been used to study the 5d ${}_{}{}^4{}_{}{}^{}$${\mathit{F}}_{9/2}$→5p ${}_{}{}^4{}_{}{}^{}$${\mathit{D}}_{7/2}^{\mathit{o}}$→5s ${}_{}{}^4{}_{}{}^{}$${\mathit{P}}_{5/2}$ cascade in Kr ii and the 6d ${}_{}{}^4{}_{}{}^{}$${\mathit{F}}_{7/2}$→6p ${}_{}{}^4{}_{}{}^{}$${\mathit{D}}_{5/2}^{\mathit{o}}$→6s ${}_{}{}^4{}_{}{}^{}$${\mathit{P}}_{3/2}$ cascade in Xe ii. A neutral atomic beam was excited and ionized by electron impact, and the spontaneously emitted photons were collected by an ellipsoidal mirror and detected by fast photomultipliers provided with narrow-band interference filters. The spectrum of time delays was acquired by a time-to-amplitude converter and multichannel pulse-height analyzer. The lifetime of the Kr ii 5p ${}_{}{}^4{}_{}{}^{}$${\mathit{D}}_{7/2}^{\mathit{o}}$ state was found to be 7.004±0.053 ns. This is in agreement with two previous high-precision measurements and represents an improvement in precision by a factor of 3.6. The Xe ii 6p ${}_{}{}^4{}_{}{}^{}$${\mathit{D}}_{5/2}^{\mathit{o}}$ lifetime was found to be 9.494±0.067 ns. This result agrees with several measurements of lower accuracy, but is in clear disagreement with two previous measurements claiming high precision, which disagree with each other as well.

• Received 10 December 1991

DOI:https://doi.org/10.1103/PhysRevA.45.4452