NDN acknowledges support from the USGS National Cooperative Geologic Mapping Program. The manuscript was improved following the critical comments we received from C.
A wide variety of minerals have been fission-track dated, as have natural and artificial glasses.
This is a special type of dating method that makes use of a microscope rather than a mass spectrometer and capitalizes on damaged zones, or tracks, created in crystals during the spontaneous fission of uranium-238.
The fission process results in the release of several hundred million electron volts of energy and produces a large amount of radiation damage before its energy is fully absorbed.
The damage, or fission tracks, can be made visible by the preferential leaching (removal of material by solution) of the host substance with a suitable chemical reagent; the leaching process allows the etched fission-track pits to be viewed and counted under an ordinary optical microscope.
The fragments emitted by this fission process leave trails of damage (fossil tracks or ion tracks) in the crystal structure of the mineral that contains the uranium.
The process of track production is essentially the same by which swift heavy ions produce ion tracks.Fission-track dating is a relatively simple method of radiometric dating that has made a significant impact on understanding the thermal history of continental crust, the timing of volcanic events, and the source and age of different archeological artifacts.The method involves using the number of fission events produced from the spontaneous decay of uranium-238 in common accessory minerals to date the time of rock cooling below closure temperature.The sample is bombarded with slow (thermal) neutrons in a nuclear reactor, resulting in induced fission of uranium-235 (as opposed to spontaneous fission of uranium-238).The fission tracks produced by this process are recorded by a thin plastic film placed against the surface of the sample.A special feature of fission-track dating lies in its ability to map the uranium distribution within mineral grains.