Dating water and tracing bones to high precision will be more widely
available for geological and biomedical applications thanks to state-of-the-art
atom counting techniques.
In a pair of new papers, Zheng-Tian Lu of Argonne National Laboratory
(firstname.lastname@example.org) and his colleagues have demonstrated two new applications
of Atom Trap Trace Analysis (ATTA; see Update
460), in which researchers trap desired isotopes with lasers and
magnetic fields and then count them with laser techniques.
ATTA has now been used to count krypton-81 atoms in groundwater samples
in the ancient waters of the Sahara. Kr-81 (half life=229,000 years)
is a rare isotope produced by the cosmic rays in the atmosphere, and
accompanies more common forms of atmospheric krypton.
Trapped in water underneath the Sahara, the abundance of Kr-81 relative
to other Kr isotopes provides information on how long the water has
been there. Extracting krypton from the Nubian aquifer in the western
Sahara, and using the ATTA technique, the researchers found that the
water's age ranges from 200,000 to a million years old, depending upon
the sample location.
In another application, researchers used ATTA to count individual calcium-41
atoms released from the bones of a human subject. This isotope is injected
into osteoporosis patients and subsequent measurements of its abundance
can be used to monitor bone loss and retention rates. Until now, medical
researchers had to rely upon particle accelerators to perform this task.
But the smaller and potentially cheaper ATTA is now precise enough
to do the job, with the ability to detect one Ca-41 atom per 108-1010
calcium atoms. With further increases in precision (in which one Ca-41
atom can be detected amidst 1015 other calcium atoms) the
technique could be ideal for archaeological dating (half-life of Ca-41
= 103,000 year) of ancient bones ranging from 50,000 to 500,000 years
et al., Geophysical Research Letters, 12 March 2004;
and Moore et al., Physical Review
Letters, upcoming article; see news
release on GRL paper.)