Resonance ionization spectroscopy and the detection of 81Kr

Development of resonance ionization spectroscopy (RIS) has made the concept of single-atom counting, whether radioactive or stable, practical for most elements of the periodic table. Tunable narrow-band lasers are used to efficiently and selectively excite and ionize a chosen element without interference from the much more abundant background, thereby achieving sensitivity at the level of a few atoms. Applications of the selectivity and sensitivity of RIS are numerous, including the direct analysis of solid, chemically processed liquid and noble gas samples. For example, 81Kr, a 2.1 × 105 year half-life cosmogenic radioisotope was detected with less than 400 81Kr atoms in the RIS analysis system