α-ejection correction
α-decay of 238U, 235U, 232Th
and 147Sm is associated with kinetic energies of 4-8 MeV.
α particles with such high energies travel on average 20 μm in
apatite before coming to rest. This results in a loss of 4He,
which must be corrected for through division by the α-retention
factor Ft, which can be calculated by polynomial approximation.
A common mistake is to apply the α-ejection correction after
the age calculation, i.e. by dividing the uncorrected age by Ft.
This leads to a partial linearisation of the age equation and a loss of
accuracy. To ensure optimal accuracy, either divide He by Ft
or multiply U, Th and Sm with Ft before entry into HelioPlot's
input table (Vermeesch, 2008; Ketcham, 2009).
See entering data,
importing data