Accuracy testing using thick source alpha-particle spectroscopy for the U and Th series estimations

Full text: The new technique for the calculation of U and Th based on the alpha particle spectrum taken from a thick sample by using a silicon detector (PIPS) is tested and some technical problems are encountered and also some notifications for better accuracy are addressed. This technique which is manly useful for dose rate determination in TL, OSL and ESR dating applications, gives also the possibility for detecting and estimating possible disequilibrium in U and Th series and thus increasing the accuracy of the calculations even in the range of some decimals of ppm. The validity of the basic equation of the new technique is tested using this for different energy intervals and comparing the results. This equation, Nm (4nInt)/(R1 - R2), gives the number of alpha particles Nm (Bq/g) emitted by the radionuclides of the U and Th series (activity concentration) per unit mass per unit time (s) with energies higher than a certain value E (MeV), where nInt is the integral of counts per unit surface (cm2) per unit time (Ks) in the energy interval between E1 and E2 and R1, R2 (mg/cm2) are the ranges in the sample corresponding to E1 and E2, respectively. This interval must be everywhere between E and the next lower energy of the emitted alpha- particles by the two series. The usually small peaks of the spectrum observed in some porous samples which correspond to energies of 220Rn and 222Rn and their daughter nuclides emitted from the sample in the space between the sample and the crystal are experimentally studied and modifications in order to overcome related problems are discussed