The relation connecting the concentration of uranium and thorium atoms
in geological samples with alpha-track production rates in plastic tr
ack detector LR-115 type II and fission track rates in Lexan has been
used for the analysis of radioactive fossil bones. The track measureme
nts fran the samples under secular equilibrium define the total uraniu
m and thorium concentrations whereas fission track measurements yield
uranium concentration alone. Combining both the measurements uranium a
nd thorium contents are determined.