Gross Alpha and Beta Counting with LSC Systems

A great number of samples are to be counted at radiation laboratories to ensure proper routine operation of nuclear facilities. In normal operation most of the samples are expected to be "clean.

Gross alpha/beta analysis is mostly applied as the first step (Jobbagy et al. 2010). One of the popular methods is to use proportional counters (PC), but the self-absorption, especially of alpha particles, limits the sensitivity and accuracy. Furthermore, tritium cannot be measured due to its volatility and very low beta energy.

To overcome these shortcomings, liquid scintillation counting (LSC) may be employed. In order to facilitate the handling of the many samples needed to be processed, a first stage which includes a fast screening procedure that is based on the counting results in three windows of a LSC system was applied. Only samples which do not pass the first stage are processed for more analysis.

The liquid scintillation measurements were performed by operating a basic LSC system, model Tricarb TR 1900 manufactured by Packard Instrument Comp.

Three windows of a LSC system were used: the first energy window (A) for tritium counting (Emax=18 keV), the second energy window for beta emitters (B), defined between end of window (A) and 2000 keV. In spite of their higher energy, alpha particles will produce pulses in the area of mid-energy. Equivalent energy range of 30-300 keV was assumed for window C, the "alpha window".

The performance of the LSC system is superior for most practical quenching levels.

Taking into consideration the reduced work and time needed for sample preparation and the need to apply LSC in any case of tritium presence, the LSC is the chosen method when performing fast screening for gross alpha and beta emitters.