Measurement of U and Th concentrations in environmental samples through detection of alpha particles emitted by isotopes in the U and Th decay chains.
Alpha particles emitted during radioactive decay are extremely short range (in minerals, micrometers) but deposit a significant quantity of energy. Therefore, the isotopes responsible for alpha emissions may be a large contributor to the overall absorbed radiation dose for a datable sample.
In order to measure the U and Th concentrations in a mineral, the sample is ground to a powder and deposited on a scintillator screen (mounted to a photomultiplier tube) or on to a semiconductor detector. Alpha particles deposit significantly more energy than beta particles or gamma rays, so unwanted counts are rejected through electronic processing of the signals recorded by the detector.
Although thin samples would provide better energy resolution (essentially no loss of energy due to...