Datación por trazas de fisión
(fish’ ∂n trak) A method of calculating age by measuring the track density left by spontaneous splitting of 238U. Tracks show the physical damage to mineral grains produced by spontaneous fission of 238U. The number of tracks is proportional to the isotope’s concentration and the age. The tracks are made visible under electron microscope by etching a thin sample with acid. The 238U count is obtained by the 238U/235U ratio and neutron irradiation that causes 235U to fission.