Important criteria for the dating of apatite by (U Th)/He are the presence of moderate radionuclide concentrations (tens of ppm) and a minimum abundance of inclusions.
Few areas of science have posed a greater challenge to Young-Earth Creationism than radiometric dating of rocks and minerals.
To counter the conclusions of radiometric dating creationists have formed the RATE (Radioisotopes and the Age of the Earth) Group.
This team, supported by several creationist organizations, exists to disprove the validity of radiometric dating.
These tests which were mainly performed in the early 1960s, led to an increase of tritium in precipitation over the continents of the northern hemisphere from roughly 5 TU to levels of the order of 1000 TU.
By measurement of the amount of radiogenic He in an apatite sample, and the amounts of uranium and thorium present, a (U-Th)/He age can be determined (see reverse).
These ages are progressively reset by heating, due to the diffusive loss of the radiogenic helium (analogous to the annealing of fission tracks), with total loss occurring at temperatures around 80 to 90C (for timescales involving millions of years).
One TU (Tritium Unit) means a tritium to hydrogen ratio of 10.
Whereas the addition of bomb tritium to the environment practically eliminated the use of natural tritium as a tracer, it offered a new tool, i.e., the use of the bomb tritium peak (Fig.