[en] The research results have demonstrated that extending collinear fast beam laser spectroscopy to resonance-excitation field-ionization spectroscopy yielded a novel ultrasensitive method to identify minute amounts of radioactive and stable isotopes. The authors have mainly performed measurements involving the trace detection of the various isotopes of Kr, Tl and Xe. In particular the technique is capable to monitor the long-lived radioactive isotopes used as tracers in the well logging industry and also in the biosphere in a range, where nuclear radiation counting techniques do not have the required isotopic selectivity and sensitivity. The authors are working in two directions. Both applications are based on the ultra sensitive detection of ⁸⁵Kr, namely: trace detection of ⁸⁵Kr to map the reservoir structure of large oil fields; trace detection of ⁸⁵Kr in environmental air samples to monitor nuclear activities and nuclear materials processing on a global scale. The authors are in contact with the BP company for practically implementing the oil field related work and have asked for samples from their Alaskan fields