It is a dating method that incorporates uranium as the center of the mechanism. The uranium-bearing fragments have trails or tracks and can be studied. They give away a pattern that is studied by geologists and can be used to date specimens. It capitalizes on damaged zones or tracks which are created as spontaneous crystals erupt during the spontaneous fission of uranium.
The technique relies on a microscopic approach rather than a macroscopic approach, using the degrading trails as an indicator of the age of the specimen. Of course, it is only valuable and authentic if you have comparable data to evaluate different patterns and figure out the age of the specimen.
To understand fission track dating, you must first understand what fission tracks are. Fission tracks are linear structures formed in rock crystals. They form due to the spontaneous radioactive decay of U-238(Uranium) into two Pd-119(Palladium) daughter atoms. These structures are extremely small to be noticed by the naked human eye and have a size range of 10^(-6) meters or 0.000001 m.
These structures can, therefore, be noticed under a compound microscope. The dating method involves studying the ‘damage’ done by these spontaneously decaying U-238 atoms. The tracks are first made visible using preferential leaching. The number of pre-existing fission tracks is then counted.
Second, the content of uranium present is found out by using irradiating the sample with neutrons. The irradiation causes spontaneous fission of U-235 atoms. The number of newly formed fission tracks are counted again. These induced tracks are then compared in a ratio. U-235: U-238 is a commonly known ratio and is assumed to be constant in nature.
The ratio of spontaneous to induced tracks is proportional to the age of the sample.
Fission track dating method is an outdated method for finding out the age of rock crystals because of its major drawbacks. The tracks that are studied are damaged by annealing and not all materials necessarily have a significant amount of Uranium impurities. The only materials whose age is studied with this method are zircon and glass due to abnormally high uranium content in their natural samples.
One advantage of the fission track dating method is the fact that fairly low amounts of sample are needed and they tend to have low contamination issues while being studied.