Lehmann, BernhardBernhardLehmannOeschger, H.H.OeschgerLoosli, Heinz HugoHeinz HugoLoosliHurst, G. S.G. S.HurstAllman, S. L.S. L.AllmanChen, C. H.C. H.ChenKramer, S. D.S. D.KramerPayne, M. G.M. G.PaynePhillips, R. C.R. C.PhillipsWillis, R. D.R. D.WillisThonnard, N.N.Thonnard2024-09-022024-09-021985https://boris-portal.unibe.ch/handle/20.500.12422/43325A new analytical technique with sufficient sensitivity to determine 81Kr concentrations in groundwater is described. The method utilizes single-atom counting by laser resonance ionization spectroscopy (RIS) in combination with a small mass spectrometer to achieve the required selectivity and sensitivity. A first demonstration of the technique for groundwater analyses is presented in which about 1000 atoms of 81Kr were counted after the processing of gas extracted from only a few liters of water. The potential of the new method for groundwater dating in the range 50,000 to 1,000,000 years is discussed.en500 - Science::530 - Physicsarticle10.48350/15871110.1029/JB090iB13p11547