Improvements of the branching ratio technique with accurate atomic data

Abstract

The branching ratio technique for radiometric calibrations in the vacuum ultraviolet is reviewed. Some examples of recent applications are given, and extensions of the method to enlarge its range are discussed. This method is based on the availability of transition probability data for pairs of suitable atomic transitions, and its success depends critically on the quality of these data; furthermore, the ratio of the two transition probabilities should not be extremely large or small. Early uses of the branching ratio technique often suffered from rather inaccurate transition probability data. It is shown that with the recent arrival of powerful comprehensive atomic structure calculations and some very accurate new experimental emission and lifetime data, the availability of highly accurate transition probability data has greatly increased. Especially for helium-, lithium-, beryllium-, boron-, and carbonlike ions many available data are now of an accuracy that permits applications of this technique that are precise to with 5–10%.