The etching of alpha-recoil tracks in phlogopite

This work uses three phlogopite samples to investigate the etching behavior of alpha-recoil tracks (αα-recoil tracks), which is a key problem in dating procedures. At the initial stage of the etching process, the number of alpha-recoil tracks increased linearly with etching time, then the linearity was interrupted due to the overlapping of alpha-recoil tracks. The slope of the etching line could be similar and also could be different both in the same sample and in different samples. It is shown that the etching time could vary with different contents of U and Th and could not exceed 200  min in 4% HF acid at 25±1∘C in order to get a satisfactory etching line and to calculate the exact density. We propose two valid methods that can accurately determine the position of the sample's surface and may reduce the alpha-recoil track dating errors.