The effect of quench on Quantitating Alpha Radionuclides by Liquid Scintillation Counting


Courtesy of PerkinElmer, Inc.

Detecting and quantitating alpha emitting radionuclides are routine tasks in nuclear energy and environmental monitoring. For this purpose, liquid scintillation counting (LSC) is an excellent method because alphas are counted with nearly 100% counting efficiency with low backgrounds, even with severe quenching. Quenching agents such as inorganic acids, organic acids, and extractive scintillators are often required to prepare samples when assaying high-level radioactive waste. Spectral data show that in spite of a shift to lower energy and a general broadening of the spectra, 100% counting efficiency is maintained for alpha nuclides. Extractive scintillators show improvement in alpha resolution compared to cocktails containing emulsifiers However, resolution generally degrades with an increase in quench. This effect of quench on counting efficiency and resolution for alpha emitters is discussed.

With increased concern about radionuclides in the environment, it has become increasingly important to accurately quantitate alpha emitters. Nuclear fuel fabrication and processing, nuclear reactor operation, radioactive ore mining operations, waste storage facilities, and environmental monitoring laboratories detect and quantitate alpha activity. Liquid scintillation is often the method of choice when high throughput screening for the presence of alpha activity is required. In fact, recently the U.S Environmental Protection Agency (E.P.A.) has validated the method (E.P.A. 40 CFR Parts 141 and 142, National Primary Drinking Water Regulations) for the measurement of gross alpha activity for 226Ra, 222Rn, and Uranium in drinking water. Liquid scintillation has recently been applied to the assay of transuranium elements in high-level radioactive waste.8 This study explores the effect of quench on alpha counting efficiency and resolution.

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