Who discovered fission track dating

30-Sep-2016 11:25

In 1906, Sir Francis Galton visited a county fair in which a contest was held to guess the weight of an ox. Galton discovered that the average of all their estimates (1,197 lbs) was significantly closer to the true weight of the ox (1,198 lbs) than any of the individual estimates (Figure 2a). Similar effects are seen in fission track geochronology, which is a geological dating technique based on the manual counting of damage tracks created by the sponteous fission of $^{238}$U in uranium-bearing minerals.

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An age can be calculated by (a) counting the surface density (in tracks per unit area) of the fission tracks with an optical microscope, (b) mathematically converting this surface density to a volume density (tracks per unit volume), and (c) measuring the U-content (atoms per unit volume) of the same surface. U damages the crystal lattice of minerals, bottom: polishing mineral grains to reveal an internal surface and etching it with acid reveals the fission tracks to the human eye; (b) a real-world example of fission tracks in apatite. With time, the density (tracks per unit area) of these so-called 'fission tracks' increases at a rate that is proportional to the U-concentration of the mineral. Although fission tracks are are too small to see with even the most sensitive microscopes, they can easily be revealed by acid etching.

Apatite and zircon are two minerals which are commonly found in rocks such as granite, sandstone and gneiss, and contain up to 0.1 weight percent of uranium. 99.9998% of this naturally occurring uranium undergoes radioactive decay by disintegrating into eight He-nuclei and a Pb atom at a precisely known rate, forming the basis of the U-Pb and U-Th-He clocks.