The effect of sample stability on the determination of radioactivity for various radionuclides by liquid scintillation counting

• The variation of quench level over time can be an indication of sample stability.
• The sample stability has impact on α/β discrimination as well as on the counting efficiency.
• Special attention should be paid to the radionuclides with chemical form apt to be adsorbed.
• Shaking a sample and checking the LSC spectra can give the information on physical quench.
• Significant physical quench usually leads to a new peak in the LSC spectrum of an α emitter.

For measuring a sample stored for a long period of time using liquid scintillation counting (LSC), it is necessary to study the long-term stability of the sample. The effect of sample stability on the determination of radioactivity for 241Am, 90Sr/90Y, 137Cs, 147Pm, 237Np/233Pa, and 3H by LSC has been investigated. The variation of quench level over time can be an indication of sample stability. If the variation in a sample is little, the effect of sample stability on the determination of the above radionuclides can be neglected. Otherwise, the sample stability will have impact not only on the counting efficiency (especially for low energy β emitters), but also on the results of α/β discrimination. For studying the stability of a sample, special attention should be paid to the radionuclides with chemical form apt to be adsorbed, because the quench level of a sample cannot be reflected by the quench index SQP(E) alone when significant physical quench exists. Shaking a sample stored for a long period of time and checking the LSC spectra can give the information on physical quench in the sample. In the range of this study, OptiPhase Hisafe 3 has much better quench resistance than Ultima Gold AB.