Dating water and tracing bones

Are two new applications of atom-trap trace analysis. Through the ATTA technique, researchers use lasers and magnetic fields to trap atoms of specific rare isotopes and then, with lasers, count them one at a time. In a pair of recent papers, Zheng-Tian Lu of Argonne National Laboratory worked with international collaborations to count krypton-81 atoms in ancient groundwater samples from beneath the Sahara Desert in Egypt and calcium-41 atoms released from human bones. The researchers found—using⁸¹ Kr’s half-life of 229 000 years—that the water trapped in the Nubian aquifer ranged in age from 200 000 to a million years old, depending on the sample location. In the biomedical application, ⁴¹Ca was ingested by a female subject, and subsequent measurements of the isotope’s abundance were used to monitor bone loss and retention rates. With ATTA, the researchers could detect one ⁴¹Ca isotope per 10⁸–10¹⁰ calcium atoms. With further improvements, the technique could be ideal for archaeological dating (⁴¹Ca’s half-life is 103 000 years) of ancient bones up to a million years old. (N. C. Sturchio et al., Geophys. Res. Lett. 31, L05503, 2004 http://dx.doi.org/10.1029/2003GL019234 ; I. D. Moore et al., Phys. Rev. Lett. 92, 153002, 2004.http://dx.doi.org/10.1103/PhysRevLett.92.153002 )