Liquid scintillation counting (LSC) is a major technique not only for measurement of pure beta emitting radionuclides, but also radionuclides decay by electron capture and alpha emission. Although it is a conventional radiometric technique, but still a competitive techniques for the measurement of many radionuclides. This paper summaries the major development of this measurement technique in instrumentation, methodology and applications in the past decades. The progresses in the instrumentation and methodology mainly focus on the commercialization of triple-to-double coincidence ratio based LSC techniques and its application in the determination of different radionuclides. An overall review and discussion on the LSC based analytical methods for the determination of major radionuclides in environmental researches, decommissioning of nuclear faculties and nuclear application are presented, in both measurement techniques and sample preparation using radiochemical separation. Meanwhile the problems and challenges in the development and application of the LSC are also discussed.

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Liquid scintillation counting for determination of radionuclides in environmental and nuclear application

Liquid scintillation counting (LSC) is a major method for the measurement of beta-emitting and some alpha-emitters. It has been applied in many aspects such as the monitoring of environmental radioactivity, the behavior of radionuclides in the environment, and the characterization of nuclear waste for the decommissioning of nuclear facilities. Radionuclides are also widely applied to the investigation of environmental processes. However, the level of radionuclides in the environment is normally very low, and the resolution of LSC alone is not sufficiently high to identify and quantitatively measure different radionuclides. Low background LSC and chemical separation and purification are needed. This chapter aims to present the principles of LSC measurement techniques for the above purposes and focus on the practical issues in the LSC determination of environmental radionuclides, as well as the status of the present research progress in these aspects. The principles of low-level counting using LSC including the methods for reducing the background in the LSC instrument and practical issues in sample preparation are presented. The principles and applications for the measurement of alpha-emitters using LSC with the alpha/beta discrimination features are presented. The main application of triple-to-double coincidence ratio–based LSC in normal and Cerenkov counting models are also described. Most of the effort of this chapter focuses on the application of LSC in the determination of different anthropogenic and naturally occurring radionuclides, including tritium, 14C, 55Fe, 63Ni, 89,90Sr, 90Y, 99Tc, 241Pu, 36Cl, 41Ca, 129I, 210Po, 210Pb, isotopes of uranium, thorium, radium, and radon. Besides the LSC measurement methods, the detailed and practical chemical separation of these radionuclides from different sample matrices, as well as the sample preparation methods for LSC measurement are discussed based on the open publications and the experiences of the authors.

Environmental liquid scintillation analysis

This paper reports the results obtained during an intercomparison exercise for the determination of difficult to measure radionuclides in activated reactor pressure vessel (RPV) steel samples. In total, eight laboratories participated analysing 14C, 55Fe and 63Ni activity concentrations in RPV steel. In addition, some laboratories also analysed 60Co activity concentrations. Corresponding activity concentrations were also determined using activation calculations. Robust statistical techniques were utilised for the analysis of the results according to ISO 13528 standard. The results showed good agreement for 55Fe and 63Ni results whereas 14C results had significant differences. 60Co results were in quite good agreement.

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Intercomparison exercise on difficult to measure radionuclides in activated steel: statistical analysis of radioanalytical results and activation calculations

This paper reports the results obtained in a Nordic Nuclear Safety Research project during the second intercomparison exercise for the determination of difficult to measure radionuclides in decommissioning waste. Eight laboratories participated by carrying out radiochemical analysis of 3H, 14C, 36Cl, 41Ca, 55Fe and 63Ni in an activated concrete. In addition, gamma emitters, namely 152Eu and 60Co, were analysed. The assigned values were derived from the submitted results according to ISO 13,528 standard and the performance assessments were determined using z scores. The measured results were compared with activation calculation result showing varying degree of comparability.

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Intercomparison exercise on difficult to measure radionuclides in activated concrete - statistical analysis and comparison with activation calculations

A method for sequential determination of 55Fe and 63Ni in leaching solution of cement solidification using liquid scintillation counting (LSC) was developed. In this method, 55Fe and 63Ni were first precipitated in the form of hydroxide and subsequently purified by anion exchange chromatography and dimethylglyoxime precipitation. After the purification, 55Fe and 63Ni were determined by LSC. The performance of the method was examined, and minimum detectable activity concentration was determined to be 0.82 Bq L−1 for 55Fe and 0.42 Bq L−1 for 63Ni in leaching solution samples with a counting time of 1 h. High decontamination factors for 55Fe and 63Ni were also obtained.

Method for sequential determination of 55 Fe and 63 Ni in leaching solution from cement solidification

A comparative study using liquid scintillation counting was performed to measure 63Ni in low and intermediate level radioactive waste. Three dimethylglyoxime (DMG)-based radiochemical procedures (solvent extraction, precipitation, extraction chromatography) were investigated, the solvent extraction method being considered as the reference method. Theoretical speciation calculations enabled to better understand the chemical reactions involved in the three protocols and to optimize them. In comparison to the method based on DMG precipitation, the method based on extraction chromatography allowed to achieve the best results in one single step in term of recovery yield and accuracy for various samples.

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Cécile Garcia

Papers

A comparative study using liquid scintillation counting to determine 63Ni in low and intermediate level radioactive waste