MEASUREMENT OF THE ATOMIC LIFETIME OF KR-II 5P 4D7/2(0) AND XE-II 6P4D5/2(0) USING THE CASCADE-PHOTON-COINCIDENCE TECHNIQUE

A high-efficiency cascade-photon-coincidence lifetime-measuring apparatus has been used to study the 5d4F9/2 --> 5p4D7/2-degrees --> 5s4P5/2 cascade in Kr II and the 6d4F7/2 --> 6p4D5/2-degrees --> 6s4P3/2 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 5p4D7/2-degrees 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 6p4D5/2-degrees 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.