On the significance of the measurement evaluation method in decision making: A synthesis of JCGM 101 and JCGM 106 applied to gross alpha and gross beta measurements using LSC

In decision making, e.g. conformity to a specification like a reference value or a requirement, the decision rule applied shall be documented. Furthermore, if the measurement uncertainty is considered in the decision process the associated probability, or risk, that a measurement result is above (or below) a reference value shall be taken into account. In this work it is shown that for gross alpha and gross beta measurements the evaluation method, GUMUF (GUM Uncertainty Framework) or MC (Monte Carlo), may also be important and influence the decisions taken when measurement results are very close to the reference value. Therefore the evaluation method and assumptions of the input quantities may also be important to document. Moreover, decision makers or users of measurement results should be aware of possible differences and/or consequences due to the evaluation method regardless of the decision rule and the choice of evaluation method.

Determination of the absolute intensity of the 1205 keV γ-ray emission from 91Y

A radiochemically pure solution of 91Y was produced by the thermal neutron fission of 235U followed by successive chemical separations to remove fission product impurities. The gamma emission rate of the 91Y 1205 keV gamma was measured using multiple high purity germanium gamma spectrometers previously calibrated for counting efficiency using a certificated mixed nuclide gamma standard. The activity concentration of the 91Y was subsequently standardised by liquid scintillation counting. From the combination the activity concentration and gamma emission intensity, the absolute intensity of the 1205 keV gamma emission was derived as 0.2297(39)%. This data agrees within the quoted uncertainties with the absolute intensity of 0.26(4)% published in nuclear data sheets A=91 (Baglin, 2013), but reduces the uncertainty by an order of magnitude.

Activity standardization of 32Si at PTB

Within the scope of the SINCRON project, several 32Si solutions were measured by means of liquid scintillation (LS) counting techniques at PTB to determine the activity concentration. Initial results revealed limited long-term stability of the samples, and a discrepancy between the TDCR method and the CIEMAT/NIST efficiency tracing method was found. In some cases, the sample instability could not be completely avoided but there is evidence that the results of the first measurements which are carried out within a few days after sample preparation can be used for an activity determination, though with increased uncertainty. Various sample compositions were tested, and a systematic study of long-term measurements and further experiments indicates that the sample instability is due to an adsorption-like effect. The discrepancies between the two LS methods were significantly lower when measuring other 32Si solutions. The initially observed discrepancies are likely due to low-energetic radioactive impurities that can be present in some of the 32Si solutions. A spectral analysis supports the thesis that tritium is present in the first solution and even allows a rough quantification of the activity ratio A(3H)/A(32Si/32P). This value allows impurity corrections to be applied, which leads to a noticeable improvement in the agreement between TDCR and CIEMAT/NIST efficiency tracing. Finally, a new LS sample composition with 15 mL Ultima Gold and 1 mL of HCl (0.5 mol/L) was found to yield stable LS samples. The activity determinations presented in this paper represent a fundamental step towards a new 32Si half-life determination in the framework of the SINCHRON project.

Activity standardization of 60Co and 106Ru/106Rh by means of the TDCR method and the importance of the beta spectrum

Atomic and nuclear data represent an important input for the accuracy of primary activity measurements based on liquid scintillation. In particular, the reliability of β-spectrum computation has been investigated for several years through experimental and theoretical studies providing solid evidence for the need to consider the atomic effects. In the present study, the activity standardization of two β-emitting radionuclides (60Co, 106Ru/106Rh) was carried out by means of the 4πβ-γ coincidence and Triple-to-Double Coincidence Ratio (TDCR) methods. The comparison between the activity concentrations given by both primary techniques presents new evidence that a better agreement is obtained when the exchange and screening effects are included in the β-spectra implemented in the model of light emission for TDCR measurements. A new development of a stochastic model based on Geant4 simulations for TDCR calculations is also presented.

Cross-validation of standardisation techniques at ANSTO using cobalt-60 and learnings from the presence and identification of non-gamma-ray emitting impurities

To fulfil the technical requirements for accreditation to ISO/IEC 17025, the end-to-end validation of all processes associated with standardising 60Co, including gravimetric source dispensing, primary standardisation by the 4π(LS)β-γ coincidence and live-timed anti-coincidence extrapolation techniques, and impurity determination were performed and documented. Pure-beta-emitting impurities in a 60Co stock solution were identified. The impact of such impurities on measurement by liquid scintillation counting and comparison in the ESIR are discussed. A fresh 60Co source was produced, standardised, and compared using the SIR.

Age dating of liquid 90Sr-90Y sources

In the context of age dating of 90Sr, the selective adsorption of zirconium ions from the mixture with strontium and yttrium by adsorbents based on TiO2 with a chemically modified surface was investigated. The general features of the separation process of strontium, yttrium, and zirconium in batch conditions were determined. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used to analyze the initial and residual concentrations of the studied cations. Separation of 90Zr and 90Sr from a liquid source containing 90Sr-90Y using adsorbents based on TiO2 was performed for the first time. The ratio of 90Zr/90Sr was measured, and the age of liquid 90Sr-90Y sources was determined. In addition, we studied the age dating of 90Sr-90Y sources using a combination of liquid-scintillation counting of 90Sr and ICP-MS measurement. The results of both methods - the method of age-dating with the chemical separation of isotopes and the combination of LSC and ICP-MS analysis - agree very well and thus serve for cross-validation. Moreover, the combination of the two methods increases the confidence in the age-dating results of 90Sr-90Y sources.

The international reference system for beta-particle emitting radionuclides: Validation through the pilot study CCRI(II)-P1.Co-60

The Bureau International des Poids et Mesures (BIPM) is developing a new transfer instrument to extend its centralized services for assessing the international equivalence of radioactive standards to new radionuclides. A liquid scintillation counter using the triple/double coincidence ratio method is being studied and tested in the CCRI(II)-P1.Co-60 pilot study. The pilot study, involving 13 participating laboratories with primary calibration capabilities, validated the approach against the original international reference system based on ionization chambers, which has been in operation since 1976. The results are in agreement and an accuracy suitable for purpose, below 5×10-4, is achieved. The pilot study also reveals an issue when impurities emitting low-energy electrons are present in the standard solution, which have a different impact on liquid scintillation counting compared to other primary measurement methods.

A bilateral comparison between LNHB and PTB to determine the activity concentration of the same 125I solution

A bilateral comparison to determine the activity concentration of the same 125I solution was organized. As electron-capture radionuclide with a rather high atomic number, 125I must be regarded as difficult to measure. The situation is partly exacerbated by the fact that some established standardization methods, like photon-photon coincidence counting, can no longer be applied due to the unavailability of appropriate equipment and expertise. One aim of this work is to compare modern liquid scintillation counting methods for the standardization of 125I. Both participating metrology institutes have used their custom-built triple-to-double-coincidence ratio (TDCR) counters and the determined activity concentrations are in excellent agreement even though the ways to analyze the data and to compute counting efficiencies were widely independent. The results also agree with the outcome of 4π-γ counting that was carried out at LNHB. In both laboratories, the measurements were complemented by measurements with several secondary standardization methods which even allow to establish a link to the CCRI(II)-K2.I-125(2) comparison started in 2004. A good agreement between the TDCR results and the key comparison reference value of the 2004/2005 comparison was obtained.

Alpha and beta spillover in liquid scintillation counting analysis of urine samples

Rapid detection and quantification of gross alpha/beta-emitting radionuclides by liquid scintillation counting (LSC) is vital in guiding response to a nuclear or radiological incidents. Liquid scintillation counters use signal pulse shape to discriminate alpha and beta events in samples but require precise optimization to minimize the spillover, or misclassification, of those events. In this study, samples at varying activity levels were analyzed by LSC to determine the effect of activity level, emitter type, and sample matrix on spillover. Analysis proved a matrix effect and a direct correlation of activity level on spillover percentage for both alpha and beta emitting-nuclides.

Uncertainty due to primary sampling of 222Rn in analyses of water

Measurement uncertainty is an important variable, to be accounted for when decisions have to be made based on measurement results. Measurement uncertainty is composed of two main components; one is related to the primary sampling, the other to the sample preparation and the subsequent analysis of the sample. The component related to the sample preparation and the analysis is commonly well evaluated in proficiency testing while there is generally no straightforward similar approach to evaluate sampling uncertainty. ISO 17025:2017 explicitly requires that testing laboratories performing sampling and analyses determine the uncertainty related to the primary sampling. In order to determine uncertainty arising in the primary sampling of ²²²Rn in water destined for human consumption, three laboratories IRE (BE), DiSa (LU) and SCK CEN (BE) initiated a joined sampling and measurement campaign. The dual split sample method in combination with ANOVA was used to evaluate the primary sampling uncertainty (precision) of the different methods. The tests showed that sampling bias is very probably, but that with good laboratory practice the sampling uncertainty precision and respectively bias can be kept below 5%.

Radiochemical Assay of Monoamine Oxidase Activity

The activity of monoamine oxidase enzymes may be quantified by measuring the conversion of a radiolabeled amine substrate to a radiolabeled product that occurs during incubation of the substrate with the enzyme in an aqueous buffer. Described herein is an established discontinuous procedure in which separation of the substrate and product is achieved by extracting uncharged aldehydes into an organic solvent, while cationic amines remain in an acidified aqueous layer. Under assay conditions designed to ensure a pseudo-linear catalytic rate for the duration of the incubation, determination of radioactivity in the organic solvent by liquid scintillation counting facilitates estimation of an initial rate for amine turnover.

Conventional Receptor Radioligand Binding Techniques Applied to the Study of Monoamine Oxidase

Designed to measure binding interactions between small molecules and receptor proteins, radioligand binding approaches may also be applied to interactions between monoamine oxidase (MAO) and its ligands. The technique may be used with tissue homogenates or with mitochondrial membranes and can provide information about binding site density, ligand affinity, binding rate constants, and binding events at sites that do not impact absorbance characteristics of the flavin cofactor and that may not be amenable to spectrophotometric studies. This overview describes the use of a cell harvester in a common filtration approach to measure binding to MAO of radiolabeled substrates, inhibitors, or allosteric ligands in saturation analyses and to take advantage of the principles of competition to obtain quantitative binding data for unlabeled ligands that may bind with much lower affinity. The quality and reproducibility of data are impacted by factors such as choice of ligand concentrations, pipetting technique, graphing and regression approaches, and scintillation counting parameters, and consideration is given to these and other factors that may influence the results.

Rapid determination of 99Tc in water samples using Ti(OH)3-TcO2 co-precipitation and TK200 resin by liquid scintillation counting

A novel method for the determination of ⁹⁹Tc in water samples was developed using stable Re as a chemical yield tracer and TiCl₃ as a reducing agent. The influences of several experimental parameters, including TiCl₃ concentration, HCl concentration and reaction time, on the reduction of TcO₄^- and ReO₄^- as well as Ti(OH)₃-TcO₂-ReO₂ co-precipitation were investigated. Tc(VII) and Re(VII) retained on TK200 resin were effectively eluted by 5 mL of 1 mol/L NH₄SCN, which can be directly mixed with the scintillation cocktail for liquid scintillation counting. The results show that the chemical behaviors of Tc and Re are very consistent in the whole procedure. The decontamination factors of potential interferences from β-emitting nuclides mainly released from nuclear fuel reprocessing plants were also evaluated, and the minimum detectable activity concentration was calculated to be 0.08 Bq/L for ⁹⁹Tc in water samples with a counting time of 2 h.

Activity standardization of two enriched 40K solutions for the determination of decay scheme parameters and the half-life

In this paper we describe experiments on two enriched ⁴⁰K solutions to accurately determine decay data. The first solution was measured in 2004/2005 by means of a gamma-ray spectrometer with low background and a liquid scintillation (LS) counter to apply the CIEMAT/NIST efficiency tracing method. A combination of results yields an emission probability of the 1461 keV gamma-rays of P_γ = 0.1030(11) which is lower than current results of data evaluations. The activity concentration of the second solution was also determined by means of LS counting, but here, the CIEMAT/NIST efficiency tracing method as well as the TDCR method were applied. Again, the result was combined with that of independent gamma-ray spectrometry and the gamma-ray emission probability was found to be P_γ = 0.1029(9) in good agreement with the result obtained from the first solution. A combination of both experiments yields P_γ = 0.1029(9). The spectra of a TriCarb LS counter were carefully analyzed and a beta minus emission probability [Formula: see text]  = 0.8954(14) was determined. The new results for P_γ and [Formula: see text] indicate that the overall probability of the decay via EC in recent data evaluations is overestimated. The LS counting efficiencies were computed with a stochastic model and up-to-date calculations of the beta spectrum and fractional EC probabilities were used. The final activity result of the second solution is combined with the outcome of a comprehensive isotopic analysis to determine the half-life of ⁴⁰K which is found to be 1.2536(27) ·10⁹ years. All above-stated uncertainties are standard uncertainties (k = 1).

Activity standardization by means of liquid scintillation counting and determination of the half-life of 89Zr

A⁸⁹Zr solution was measured by means of liquid scintillation counting techniques in order to determine the activity concentration. Two methods were used: the CIEMAT/NIST efficiency tracing method with ³H as a tracer, and the triple-to-double coincidence ratio method. The counting efficiencies were computed with a stochastic model. The very detailed investigation showed that a few corrections are particularly important: Asymmetries in the photodetector responses as well as the backscattering of high-energy gamma rays must be taken into account. Corresponding corrections have therefore been applied. In addition, a detailed uncertainty analysis was carried out and the uncertainties compared with those determined by other research groups. The activity concentrations obtained from the two methods agree well and a combined result was used to establish calibration factors for ionization chambers, which are important secondary standardization instruments. The ionization chambers were combined with a new high-precision current measurement device to provide outstanding linearity. Measurement data from one chamber were used to determine the half-life, which was found to be T_1/2=(78.373 ± 0.023) h.

Development of a rapid method for extraction of uranium from uranium bearing materials using ionic liquid as extracting agent from basic media

The paper presents the development of a rapid method for the direct determination of uranium using liquid scintillation analysis in uranium bearing materials with different uranium concentrations and with different impurity levels (U-ore, Uranium ore concentrate (UOC) and U-metal). Uranium extraction was carried out using hydrophobic ionic liquid Aliquat-336 thiosalicylate, ([A-336][TS]) from diluted samples in basic medium followed by liquid scintillation counting (LSC). Extraction efficiencies for uranium from aqueous medium was studied with very small volumes of ionic liquid under varying volume, pH and uranium concentration of the aqueous medium. Maximum extraction efficiency was achieved near pH 8-11. Uranium was successfully re-extracted from organic medium with nitric acid and electroplated onto stainless steel planchette for alpha spectrometry determination. Maximum re-extraction efficiency with 1 M HNO₃ combined with electroplating efficiency observed was 80%. The methodology was applied for real samples. The uranium extraction efficiency using ionic liquid was about 85% for U-metal and UOC samples with comparatively low impurity level; whereas extraction efficiency for U-ore samples was found to be less than 40%. The technique can be applied for nuclear forensic applications as well as nuclear emergency scenarios for a quick initial assessment and isotopic analysis of uranium in the samples.

Standardization of 226Ra solutions with descendants by 4παβ LSC counting

In this work, a method to standardize ²²⁶Ra solutions with descendants by 4παβ liquid scintillation counting (LSC) has been used. The standardization can be carried out provided that the equilibrium state of ²²⁶Ra solutions, the counting efficiency of short-lived ²¹⁴Po and/or the counter dead time are known. Procedures to obtain these requirements have been set up.

Urine strontium-90 (Sr-90) manual and automated pre-analytical separation followed by liquid scintillation counting

Responding to a radiological or nuclear incident may require assessing tens to hundreds of thousands of people for possible radionuclide contamination. The measurement of radioactive Sr is important because of its impact on people's health. The existing analytical method for urine Sr-90 analysis using crown ethers is laborious and involves possible exposure to concentrated acids; therefore, this work is devoted to the development of the automated Sr-90 separation process, which became possible with the prepFast pre-analytical system (Elemental Scientific, Inc).

Comparative evaluation of 2H- versus 3H-based enrichment factor determination on the uncertainty and accuracy of low-level tritium analyses of environmental waters

Analysis of low-level tritium (³H) in environmental waters requires pre-concentration using electrolytic enrichment prior to decay counting. Accurate and precise electrolytic enrichment factors (EF) are required to determine the sample's environmental ³H concentration. Two methods are used to determine EFs: i) the Spike Proxy Method (SPM) and ii) the Deuterium Method (DM) with each having several modalities. We conducted a comparative assessment of four EF strategies using 250 mL and 500 mL electrolytic enrichment of three low-level ³H proficiency water standards (0.5-7 TU) to see which strategy gave the most accurate ³H results based on z- and Zeta-scores. Our comparative evaluation revealed the DM offers consistently superior ³H results, with more precise EF determinations compared to the three SPM strategies. The DM gave the best z-scores with an EF relative combined uncertainty of about 0.5‰ and a negligible contribution to the overall uncertainty budget due to the EF determination. Moreover, the DM can improve productivity by eliminating the spike and gravimetric procedures from routine analyses and can give rapid cell enrichment performance feedback prior to decay counting. We recommend low-level tritium laboratories consider adopting the DM into their ³H sample enrichment and analysis operations.

Simultaneous determination of 210Pb and 210Po in seafood samples using liquid scintillation counting

The measurement of ²¹⁰Pb and ²¹⁰Po in seafood samples has attracted tremendous interest because of their radiotoxicity. In this study, a fast and cost-efficient method for the simultaneous determination of ²¹⁰Pb and ²¹⁰Po in seafood samples by ultralow-level liquid scintillation counting after separation on a Sr•spec column was developed. The recoveries of ²¹⁰Pb and ²¹⁰Po were ~70% and ~85%, respectively. The minimum detectable activity of the proposed method for ²¹⁰Pb and ²¹⁰Po was 3.85 Bq/kg and 1.50 Bq/kg, respectively, which is suitable for the determination of ²¹⁰Pb and ²¹⁰Po in seafood samples. The radiochemical procedure was validated by measuring ²¹⁰Pb and ²¹⁰Po activity concentrations in IAEA-certified reference materials and successfully applied to shrimp and clam samples.

Scintillating and wavelength shifting effect investigation of 3-methylpiridinium salicylate and its application in LSC measurements

Possible application of a novel ionic liquid 3-methylpiridinium salicylate (3-MPS) in Liquid Scintillation Counting measurements has been explored. Its addition to several radionuclides' aqueous solutions shown a significant influence on ²¹⁰Pb Cherenkov spectra, ²¹⁰Pb and ²²⁶Ra gross alpha/beta spectra, even on ³H spectra appearance. 3-MPS manifested both wavelength shifting and scintillating effect, indicating that 3-MPS or other ionic liquids of similar structure soon might be implemented into the common LSC practise as an alternative to the commercial LSC cocktails.

On the photomultiplier-tube asymmetry in liquid scintillation counters for the CIEMAT/NIST efficiency tracing method

The triple-to-double coincidence ratio (TDCR) and the CIEMAT/NIST efficiency tracing (CNET) methods are important techniques for accurate activity determination in radionuclide metrology and other fields. The methods require liquid scintillation (LS) counters with three (TDCR) or two (CNET) photomultiplier tubes (PMTs), respectively, and the original techniques assume that the responses of all PMTs in a counter system are identical. This assumption is, however, often not fulfilled. This may have significant consequences for the activity determination, and dedicated corrections are required. Corresponding effects and possible corrections for the TDCR method were discussed in a recent article (Kossert et al., 2020) while the CNET method was not included in that work. The intention of this paper is to present a brief theoretical consideration of this problem. This paper makes clear that for most radionuclides potential PMT asymmetries in CNET counters are of minor importance. In addition, measures to identify potential asymmetries in these counters are discussed.

Universal use of alpha/beta mode in liquid scintillation counting analysis for both alpha/beta and single nuclide determination

Nuclear industry advancements and growing concerns about environmental contamination and terrorist activity have increased interest in quantifying radioisotopes in environmental and human samples. Increased presence in the environment, ease of entry into the food chain, nuclear medicine applications, and the possibility of radiological terrorism incidents can lead to human intake of these radionuclides [1,2]. A universal method to screen for and quantify individual radionuclides as well as both levels of alpha and beta emitters would address these concerns.

Standardization of non-equilibrium 210Pb solutions by LSC and 2πα counting

A procedure for the standardization of ²¹⁰Pb solutions in radioactive disequilibrium, or incompletely purified from its descendants, has been set up and successfully validated. The method, based on joint measurements of ²¹⁰Po by alpha-particle spectrometry (2πα counting) with grid ionization chamber and liquid scintillation counting for overall activity estimation, is presented as an alternative to ²¹⁰Pb measurement by LSC with α/β discrimination.

Improved activity standardization of 90Sr/90Y by means of liquid scintillation counting

Radioactive strontium isotopes play an important role in environmental radioactivity. Reliable activity standards are required in order to validate radioanalytical techniques and related measurements. In this paper, improved methods for the primary activity standardization of ⁹⁰Sr/⁹⁰Y based on liquid scintillation counting are presented. To this end, two methods were used: the CIEMAT/NIST efficiency tracing technique with ³H as a tracer and the triple-to-double coincidence ratio method. Non-negligible discrepancies between the two methods were found when applying existing analysis techniques. A detailed study was carried out to identify and eliminate the causes of these discrepancies. Eventually, excellent agreement between the two methods was obtained. This required advanced beta spectrum calculations which were carried out with a specific version of the BetaShape program taking the atomic exchange effect into account. In addition, it was found that the quench-indicating parameters determined in commercial liquid scintillation counters are biased, which can cause significant problems for the CIEMAT/NIST efficiency tracing method. The effect depends on the counting rate and can be explained by a superposition of the LS spectra generated by ⁹⁰Sr/⁹⁰Y and the external standard source.

Measurement of the absolute gamma-ray emission intensities from the decay of 103Pd

Palladium-103 decays through electron capture to excited levels of ¹⁰³Rh, and especially to the 39.748-keV metastable state. A high activity palladium chloride solution was standardized by liquid scintillation, using the Triple-to-Double Coincidence Ratio method. The absolute photon emission intensities were determined by gamma-ray spectrometry using point sources prepared with the standard solution. Different detectors and measuring conditions were used to cross-reference the results. The most intense photon emission intensities are derived with about 1% relative combined standard uncertainty.

A rapid method to determine 226Ra concentrations in Marcellus Shale produced waters using liquid scintillation counting

Concentrations of naturally occurring radioactive material (NORM) in Marcellus Shale produced water presents a challenge for effective management and treatment, because of the vast fluid volumes generated. With an increased emphasis on beneficial reuse and resource recovery from the produced waters, a rapid, yet reliable, method for quantifying radium in these produced waters is needed. The high total dissolved solids (TDS) concentration introduces difficulties when measuring ²²⁶Ra by recommended EPA methods that were specifically developed several decades ago for drinking water. While other techniques for measuring radium in these high-TDS fluids have since been developed, these newer techniques often require extensive and complicated pre-concentration steps; and they thus require extensive analytical chemistry skills, utilize hazardous chemicals like hydrofluoric acid, demand long holding times or measurement times, and require high sample volumes. We present a rapid method for ²²⁶Ra measurements in high-TDS produced waters by liquid scintillation counting, which has been corroborated herein by concurrent gamma spectrometry analyses. Samples were prepared for analysis by evaporating the fluid and re-suspending the evaporate with acidified distilled deionized water prior to liquid scintillation counting for 1 h. This protocol yielded radium recoveries ≥93%. Per this protocol, the alpha and beta spectra of ²²⁶Ra and its daughters were computationally separated by alpha-beta discrimination and spectrum deconvolution. The minimum detectable activities of ²²⁶Ra was 0.33 Bq/L (9.0 pCi/L) when the counting time was 60 min and the sample volume was 4 mL. Nine produced waters of varying TDS and radium concentrations from the Marcellus Shale Formation were analyzed by this method and compared with gamma spectroscopy; and these yielded comparable results with an R² of 0.92. The reduced sample preparation steps, low cost, and rapid analysis position this as a well-suited protocol for field-appraisal and screening, when compared to comprehensive radiochemical analysis. We offer that for a given produced water region, routine and local liquid scintillation analyses can be compared and calibrated with infrequent gamma spec analyses, so as to yield a near-real time protocol for monitoring ²²⁶Ra levels during hydrofracturing operations. We present this as a pragmatic and efficient protocol for monitoring ²²⁶Ra when produced water samples host low levels of ²²⁸Ra-since the progeny of ²²⁸Ra can significantly confound the LSC analyses.

Alpha spectrometry and liquid scintillation counting for the measurement of 238Pu, 239Pu, 240Pu, 241Pu, 242Pu and age

A method for the measurement of the isotopic composition and time since last chemical separation (age) of plutonium is presented. The method includes alpha spectrometric measurement of ²³⁸Pu, ²³⁹Pu and ²⁴⁰Pu where the ratio of ²³⁹Pu and ²⁴⁰Pu was determined using spectral deconvolution, and liquid scintillation counting of ²⁴¹Pu, after chemical separation of plutonium and americium. For the age determination, the ²⁴¹Pu determined using liquid scintillation counting was combined with alpha spectrometric measurement of ²⁴¹Am. The results of the isotopic composition were compared with certified reference materials with known isotopic composition, and the results of the age determination were compared with literature values of the separation dates.

Method development for rapid quantification of Rn-222 in surface water and groundwater

Understanding the risks of a developing unconventional hydrocarbons industry, including shale gas, to the chemical quality of surface water and groundwater involves firstly establishing baseline compositions against which any future changes can be assessed. Contaminants of geogenic origin are of particular interest and radon has been identified as one potential contaminant from shale sources. Robust measurement and monitoring of radon in water at environmental concentrations is essential for ensuring protection of water sources and maintaining public confidence. Traditional techniques for Rn-222 determination in water, such as inference by gamma spectrometry and direct alpha counting, are impractical for direct field measurement, and the relatively short half-life of Rn-222 (~ 3.82 days) means that longer analytical protocols from field to the laboratory may result in greater uncertainty for Rn-222 activity. Therefore, a rapid and low-cost method would be beneficial. We have developed and refined a laboratory procedure for Rn-222 monitoring using liquid scintillation counting (LSC). The accuracy of Rn-222 activities obtained via this procedure was evaluated by the analysis of almost 200 water samples collected from streams and boreholes as part of a detailed baseline investigation in the Vale of Pickering, Yorkshire, one potential location for future shale gas exploration. LSC was preferred for measurement of Rn-222 and had comparable accuracy to gamma spectrometry and direct alpha counting. The methodology provided a rapid, portable and low-maintenance option relative to the two established techniques and is shown to be a favourable choice for the measurement of radon in surface water and groundwater at environmental concentrations.

Low-sulphate water sample preparation for LSC detection of 35S avoiding sulphate precipitation

Information about groundwater residence times is essential for evaluating appropriate groundwater abstraction rates and aquifer vulnerabilities and hence for sustainable groundwater management in general. Naturally occurring radionuclides are suitable tools for related investigations. While the applicability of several long-lived radionuclides for the investigation of long-term processes has been demonstrated frequently, residence times of less than one year are only scarcely discussed in the literature. That is due to the rather small number of applicable radionuclides that show adequately short half-lives. A promising approach for investigating sub-yearly residence times applies radioactive sulphur. ³⁵S is continuously produced in the upper atmosphere from where it is transferred with the rain to the groundwater. As soon as the water enters the subsurface its ³⁵S activity concentration decreases with an 87.4 day half-life. This makes ³⁵S suitable for investigating sub-yearly groundwater residence times. However, the low ³⁵S activities in natural waters require sulphate pre-concentration for ³⁵S detection by means of liquid scintillation counting (LSC). That is usually done by sulphate extraction from large water samples with an anion-exchange resin (Amberlite IRA400, Cl-form), elution from the resin with NaCl, and precipitation as BaSO₄. Our study aimed at optimizing the standard sample preparation procedure by avoiding the laborious precipitation step. We suggest (i) sulphate extraction using the exchange resin Amberlite IRA67 (OH-form), (ii) elution with ammonium hydroxide, (iii) evaporation of the eluate and (iv) dissolving the resulting dry precipitate in 2 ml H₂O. In contrast to the standard approach our method results in a final sample solution of low ionic strength, which allows applying the water miscible scintillation cocktail Hionic-Fluor®. Since Hionic-Fluor accepts only aqueous solutions of low ionic strength the approach is applicable for waters with high ³⁵S/³²SO₄^2- ratios, i.e., low total sulphate sample loads (e.g. rainwater).

Assessment of radioactivity contents in bedrock groundwater samples from the northern region of Saudi Arabia

Recognizing the vast uses of water in human life, the presence of α and β particles emitting radionuclides in groundwater of northern Saudi Arabia has been evaluated as a means of water quality assessment of the region. A liquid scintillation counting technique was used to determine the gross α/β, and ²²⁸Ra radioactivities in water samples, while the radioactivity concentrations of ^234,238U and ²²⁶Ra were determined using alpha spectrometry after the separation process. Present results show that all water samples contain a higher level of gross α and β radioactivity than the WHO recommended limits; the average gross α activity is about 7 times greater than the limit value of 0.5 Bq L^-1, while the average gross β activity value is about 3.5 times greater than the limit value of 1 Bq L^-1. Correlations of TDS and pH with gross α and β radioactivity in the studied samples were investigated. The activity ratio of the measured U and Ra alpha emitters to the gross α radioactivity and the ratio of the measured β emitters to gross β radioactivity were also discussed. Furthermore, interesting information on thorium abundance and radioactive disequilibrium in U series were observed by studying the activity ratio of ²²⁸Ra/²²⁶Ra, ²²⁶Ra/²³⁸U, and ²³⁴U/²³⁸U. Although these samples are not directly used for human being drinking, and mainly used in irrigation, the higher gross α/β radioactivity may cause health risks to humans, since these radionuclides may enter the food chain through irrigation water. Thus, further radioactive risk assessment is highly recommended.

Tritium in urine from members of the general public and occupationally exposed workers in Lund, Sweden, prior to operation of the European Spallation Source

A powerful neutron source, the European Spallation Source (ESS), is currently under construction in Lund, Sweden (~90 000 inhabitants). Levels of tritium (³H) in urine were estimated in members of the public in Lund and employees at the ESS using liquid scintillation counting, to obtain baseline levels before the start of operation of the ESS. These were compared with levels in other occupationally exposed radiation workers. Both the spallation reaction in the ESS tungsten target and the activation of various materials by the protons produced by the 5 MW linear accelerator will generate tritium, which will be released into the atmosphere mainly as tritiated water (HTO). Urinary HTO activity concentrations were determined in a total of 55 individuals belonging to four different categories: ESS employees, neighbours of the ESS, members of the general public in Lund and exposed workers from other facilities. The participants were asked to provide information on their beverage intake the day before urine sampling. The urine samples were filtered on activated charcoal and distilled before analysis. The effect of sample preparation on the isotope fractionation of urine samples was investigated by isotope ratio mass spectrometry (IRMS) of ²H/¹H, which showed no influence. IRMS was also used to investigate if the ratio between the stable hydrogen isotopes (²H/¹H) could provide useful data of the origin, and hence the tritium concentration, of various types of drinking water. Urinary HTO activity concentrations determined using liquid scintillation counting (LSC) were found to be below the minimum detectable activity (MDA) of 2.1 Bq⋅L^-1 for most of the participants. Five of the workers actively handling organic tritiated material were found to have activity concentrations between 3.5 and 11 Bq⋅L^-1, which were higher than the average value in local tap water of 1.5 ± 0.6 Bq⋅L^-1. The results will be used to evaluate the radiological impact on the population from future releases of tritium resulting from the operation of the ESS.

Primary standardisation of technetium-99m by liquid scintillation coincidence counting

Technetium-99m was standardised by the 4π(LS)ce-γ coincidence extrapolation method. Sensitivity of the 4π(LS) channel to two types of radiation, namely conversion electrons and γ-rays, resulted in incorrect activity values being obtained when this was not adequately accounted for. Measurements were more robust when the LS detection efficiency was optimised, and when a γ-window setting was used that monitored the combined LS efficiency for conversion electrons and γ-rays. The primary standard was internationally compared through participation in the BIPM.RI(II)-K4.Tc99m key comparison.

Fast-response flow-based method for evaluating 131I from biological and hospital waste samples exploiting liquid scintillation detection

This paper presents a fast and automatic flow-based method to extract ¹³¹I from biological samples and hospital waste, previous to liquid scintillation detection. ¹³¹I is a radionuclide extensively used in Nuclear Medicine due to their beta and gamma disintegrations, whereby hospitals have to manage the associated waste generation. The automatic developed system is based on Lab-On-Valve (LOV) flow-technique exploiting Cl-resin (135 mg per extraction). This methodology allows performing sample extractions and measurements on the same day, since the extraction frequency takes 1.4-4 h^-1, depending on the analysed sample volume, plus up to 2 h of measurement for each vial. ¹³¹I is retained as iodine ion and eluted with sodium sulphide 0.2 mol L^-1. The maximum sample volume that can be preconcentrated is 20 mL, reaching an extraction efficiency of 85 ± 5%. The minimum detectable activity (MDA) is 0.05 Bq, showing a precision of 7% RSD (n = 5). Both, biological samples (urine and saliva) and hospital waste samples can be satisfactorily analysed by the proposed system, obtaining recoveries between 90 and 110%. The developed method is then suitable to implement in hospitals, improving the surveillance of the ¹³¹I environmental release.

A new approach for the determination of 210Pb by liquid scintillation counting

A new approach to the calibration procedure is presented, as there is no need to discount bismuth from lead spectrum when constructing the efficiency curve. This work presents two calibration methods: one considering mostly lead spectrum contributions and other that considers both lead and bismuth contributions. Both methodologies provide consistent results when evaluated in an intercomparison program. Furthermore, this methodology allows simultaneous analysis of several samples and is suitable for any type of sample after proper digestion in liquid form.

Improved approach for LSC detection of 35S aiming at its application as tracer for short groundwater residence times

The knowledge of groundwater residence times in (vulnerable) aquifers is essential for the sustainable management of the associated groundwater resources. A powerful tool for related investigations is the application of naturally occurring radioisotopes as water age indicators. However, due to the limited number of suitable (i.e. omnipresent, short-lived and easily detectable) radionuclides only few studies focus on groundwater ages below one year. A natural radionuclide that does have the potential to cover this time range is ³⁵S (87.4 day half-life). ³⁵S is continually produced in the upper atmosphere and transferred with the rain to the groundwater. Since no natural sources of ³⁵S exist in the subsurface the decrease of the ³⁵S activity concentration in such young groundwater can be used for the determination of its age. Still, ³⁵S activities in precipitation (and hence even more in groundwater) are very low and necessitate appropriate analytical protocols based on liquid scintillation counting (LSC). This turns out to be challenging due to the required large sample volumes and due to potentially high SO₄^2- loads of the samples, both limiting the range of possible applications of ³⁵S as indicator for short groundwater residence times. In the paper we present an improved straightforward LSC based approach for the detection of ³⁵S in natural water samples. We recommend using Insta-Gel Plus as scintillation cocktail for allowing a homogeneous suspension of ³⁵S-containing BaSO₄ in the cocktail. The recommended improvements in instrument setting concern the LSC (TriCarb 3170 Tr/SL) counting window, the pulse decay discriminator setting and the delay before burst setting. The settings allow measuring low activity concentrations of ³⁵S, which was previously pre-concentrated from natural water samples, containing SO₄^2- loads of up to 1500 mg with a reasonably high statistical reliability.

Standardization of I-124 by three liquid scintillation-based methods

A solution of ¹²⁴I was standardized for activity by 4πβ(LS)-γ(NaI) live-timed anticoincidence (LTAC) counting, with confirmatory measurements by triple-to-double coincidence ratio (TDCR) and CIEMAT-NIST efficiency tracing (CNET) liquid scintillation counting. The LTAC-based standard was shown to be in agreement (within k = 1 uncertainties) with previous measurements at NIST and elsewhere. Calibration settings for radionuclide calibrators were determined and a discrepancy with literature values, partially due to a calibration methodology dependent upon an erroneous setting for ¹⁸F, was identified and explained.

Determination of 79Se using a volatilisation method and liquid scintillation spectrometry

The operation of nuclear power plants generates large quantities of radioactive materials or waste, which need to be characterised before decommissioning or for final disposal in radioactive waste repositories. The nuclear operators in Slovakia must declare 19 critical radionuclides in all radioactive waste before storage in the regional waste repository. This article describes a simple and rapid method for the determination of one critical radionuclide, ⁷⁹Se, in radioactive waste. The conditions for the effective distillation of selenium from various mixtures of HCl and HBr solutions were studied. The highest selenium recoveries were achieved in a mixture of 6.5 mol L^-1 HCl and 18.3 mol L^-1 HBr in 7:1 vol ratio. The method was applied for the determination of ⁷⁹Se in radioactive concentrates and sludge samples from nuclear power plants in Slovakia. ⁷⁹Se was measured with a TRI CARB 3100 TR liquid scintillation counter.

Comprehensive study on the technical aspects of sampling, transporting and measuring radon-in-water

The European Commission's Joint Research Centre organizes proficiency tests (PT) on radon-in-water measurements. In order to optimize sampling, transport and measurement methods many tests and small scale proficiency tests have been performed. The waters from natural springs, wells were sampled on-site in glass bottles then transported cooled to the JRC and collaborating laboratories. For the material characterization standard measurement methods based on gamma-ray spectrometry, emanometry and liquid scintillation counting were used. The influence of sampling, transport and sample handling on radon-loss was tested and quantified. It was observed that parameters like container material, filling height, storage temperature and handling can lead to substantial measurement bias due to radon-loss. This high risk for radon-loss from samples can potentially be a general radioprotection problem as doses to the public may be underestimated. Regular air and road transport can be considered adequate means of transport as they have little influence on radon-loss if a suitable glass sample container with flexible cap is used and that it is completely filled. On the basis of this work, modifications to the related standard as best practices are also proposed.

Unperturbed, high spatial resolution measurement of Radon-222 in soil-gas depth profile

This work presents a method for measuring the depth distribution of ²²²Rn activity in soil gas. The method is based on the capacity of polycarbonates to absorb ²²²Rn and on the possibility of performing sensitive measurements of ²²²Rn absorbed by the polycarbonates via liquid scintillation counting (LSC). The method is the following: cylindrical holes are drilled along a metal rod and Makrofol^® N polycarbonate foils enclosed in polyethylene envelopes are placed in each hole. The rod is driven into the soil and kept for a certain time. As long as the rod is in the soil, the polycarbonate foils are exposed to the ²²²Rn concentration at their depth. At the end of the exposure the rod is pulled out and the foils are transferred to liquid scintillation (LS) vials filled with liquid scintillator. The ²²²Rn absorbed in the foils is then measured with a LS analyzer. The rod with the polycarbonate foils acts as a passive probe which senses the ²²²Rn concentration at different depths beneath the ground surface. The achievable minimum detectable ²²²Rn activity concentration with the equipment and conditions used in this study is around 12.5 kBq/m³. It can easily be lowered below 1 kBq/m³ if larger foils and low-background LS analyzers are used. Since the method does not require air sampling the depth distribution of ²²²Rn in the soil is unperturbed by the sampling. The spatial distribution and the maximum measurement depth are set by the distance between the holes and the depth to which the rod can be fixed into the ground. Results from in situ applications of the method in terrains with high ²²²Rn in soil-gas are reported, which demonstrate the feasibility and the usefulness of the proposed approach.

Determination of the activity and half-life of 227Th

Liquid scintillation samples with ²²⁷Th were prepared a few hours after the separation of the progeny. During the measurements, ²²⁷Th and its daughters are not in radioactive equilibrium. The counting efficiencies of the individual radionuclides of the decay chain differ from each other and the activity of an individual progeny relative to the activity of ²²⁷Th varies with time. Hence, the overall counting efficiency varies with time as well. The counting efficiency ε_T227h++ of ²²⁷Th and its progeny was determined by means of the CIEMAT/NIST efficiency tracing method. The free parameter is derived from the quench-indicating parameter, SQP(E), and from ³H tracer measurements. This makes it possible to compute the efficiency ε_T227h++ as a function of time. The individual efficiencies of all progeny are to be combined, taking correction factors and activity ratios into account. Thereby, a new, time-dependent correction, namely for the decay during the measurements, is applied. With this method, activity results are obtained that are stable over a long period of time. A least-squares method yields the time of the chemical separation as well as the ²²⁷Th half-life, which was also obtained by means of measurements in an ionization chamber. The weighted mean of the two methods (CIEMAT/NIST efficiency tracing and measurements in ionization chambers) was found to be T_1/2 = 18.681(9) d.

Rapid method for determination of 90Sr in biological samples by liquid scintillation counting after separation on synthesized column

A simple, rapid and cost-efficient method for determination of activity concentration of ⁹⁰Sr in biological samples with an extraction chromatographic column (crown ether on teflon powder) and following counted by liquid scintillation counting was developed in this paper. The column retained most of ⁹⁰Sr while almost all of matrix ions were removed during rinsing steps with 8M nitric acid and finally ⁹⁰Sr was eluted with deionized water, the chemical recovery of strontium is greater than 60%, almost all of matrix ions were removed by the procedure we reported. Finally the uncertainty was evaluated and minimum detectable activity of this method is 1.28Bq/kg.

The distribution of tritium in aquatic environments, Lithuania

The aim of this study is to investigate mobile radionuclide tritium (³H or T) activity dynamics in aquatic environments related to Ignalina NPP (INPP) site and water bodies located in remote areas unaffected by the INPP. The ³H excess in the INPP environment was analyzed and compared to the variable ³H background level over the period of operation of the INPP (end of 1983 - end of 2009) and during the initial stage of decommissioning (2010-2017). ³H in the INPP vicinity has been studied in the water of artificial channels related to operation of the INPP and site drainage, in natural surface water bodies and, at a smaller scale, in unconfined groundwater. This study presents an extensive ³H data set extending back to 1980, i.e. before INPP operation started. To assess the contribution of global sources to ³H dynamics, monthly precipitation was also studied, along with water from the Baltic Sea, Curonian Lagoon and Nemunas River were studied as well, all three of these located in the Lithuanian maritime zone. The ³H activity concentration in water was measured using liquid scintillation counting (LSC) techniques (direct counting and counting after enrichment). During the period of INPP operation, ³H from liquid effluent could be clearly observed in discharge channels, occurring in rather low diluted conditions, as well as in Lake Druksiai, the cooling basin, at an even more diluted level. The highest ³H activity concentration in Lake Druksiai was observed in 2003 and reached 201.3 ± 1.3 TU at a time when ³H activity concentrations in background water bodies was 9.2 ± 3.5 TU. After the closure of the INPP, the ³H liquid effluent rate reduced by approximately two orders of magnitude (from 10¹² Bq in 1991 to 10¹⁰ Bq in 2016) and when decommissioning activity commenced then the ³H activity concentration fell to that approaching the background level (19-27 TU) that can still be observed in industrial discharge and rainwater drainage channels. ³H as a result of leakage from the INPP can be observed in groundwater only in direct proximity to the INPP site near the radioactive waste storage zone.

Modification of LSC spectra of 125I by high atomic number elements

The ¹²⁵I pulse-height spectra via a liquid scintillation counter (LSC) displayed notable variations. The counting efficiencies of higher and lower energy peaks increased and decreased, respectively, with the enhancement of the amount of high atomic numbered elements within the cocktails. This tendency was ascribed to the increasing probability of the interaction of photons with the scintillation cocktail. Moreover, it was noted that the shape of a ¹²⁵I spectrum strongly depends on the amount of high atomic numbered elements.

Development of the Australian Standard for Germanium-68 by two Liquid Scintillation Counting methods

In response to the increasing application of ⁶⁸Ge/⁶⁸Ga and ⁶⁸Ga in nuclear medicine, an international comparison of activity measurement of ⁶⁸Ge in equilibrium with ⁶⁸Ga was organised. ANSTO standardised the comparison solution by the 4π(LS)β⁺-γ coincidence extrapolation and TDCR efficiency calculation methods, with excellent agreement between the two results. The primary standard was transferred to the ANSTO Secondary Standard Ionisation Chamber. Internationally traceable Australian Certified Reference Materials (ACRMs) of ⁶⁸Ge/⁶⁸Ga can now be prepared in various measurement geometries applied in nuclear medicine.

Measuring the Overall Rate of Protein Breakdown in Cells and the Contributions of the Ubiquitin-Proteasome and Autophagy-Lysosomal Pathways

In certain physiological or pathological states (e.g., starvation, heat shock, or muscle atrophy) and upon drug treatments, the overall rate of protein degradation in cells may increase or decrease. These adaptations and pathological responses can occur through alterations in substrate flux through the ubiquitin-proteasome pathway (UPP), the autophagy-lysosomal system, or both. Therefore, it is important to precisely measure the activities of these degradation pathways in degrading cell proteins under different physiological states or upon treatment with drugs. In particular, proteasome inhibitors have become very important agents for treating multiple myeloma and very useful tools in basic research. To evaluate rigorously their efficacy and the cellular responses to other inhibitors, it is essential to know the degree of inhibition of protein breakdown. Unfortunately, commonly used assays of the activities of the UPP or autophagy rely on qualitative, indirect approaches that do not directly reflect the actual rates of protein degradation by these pathways. In this chapter, we describe isotopic pulse-chase methods to directly measure overall rates of protein degradation in cells by radiolabeling cell proteins and following their subsequent degradation to radioactive amino acids, which diffuse from cells into the medium and can be easily quantitated. While pulse-chase methods have often been used to follow degradation of specific proteins, the methods described here allow quantification of the total cellular activity in degrading either long-lived proteins (the great bulk of cell constituents) or the fraction with short half-lives. Moreover, by use of specific inhibitors of proteasomes or lysosomes, it is also possible to measure precisely the total contributions of the UPP or lysosomal proteases. These approaches have already been proven very useful in defining the effects of inhibitors, growth factors, nutrients, ubiquitination, and different proteasome activators on overall proteolysis and on substrate flux through the proteasomal and lysosomal pathways.

Activity standardisation of 210Pb by 4πα liquid scintillation counting method

The activity of ²¹⁰Pb in a solution with ²¹⁰Pb-²¹⁰Po in the radioactive equilibrium was determined through its decay product ²¹⁰Po by liquid scintillation counting (LSC), which has, after separation, as a pure α emitting nuclide, detection efficiency practically equal to 1. For the separation of ²¹⁰Po from ²¹⁰Pb solution, two methods based on precipitation of Pb, and Pb with Bi, leaving Po in the solution, were introduced. The first one was precipitation of Pb in the form of Pb(NO₃)₂ from a mixture of acetic acid, toluene, water and HNO₃. The second one was based on co-precipitation of Bi and Pb with KCl from a mixture of organic solvents, where ²¹⁰Bi with ²¹⁰Pb was fixed to the precipitate. The relative standard uncertainty of ²¹⁰Pb activity concentration was estimated to be lower than 0.45%.

Standardization of 142Pr activity concentration

¹⁴²Pr (praseodymium-142), a potential radionuclide for brachytherapy, was produced after irradiating high purity natural Pr₂O₃ powder in a research reactor. The irradiated powder was then dissolved in acids and diluted for measurement. Several radioactivity measurement methods were used in the standardization of ¹⁴²Pr radionuclide. This work reports the results of standardization of ¹⁴²Pr with CIEMAT/NIST efficiency tracing method, gamma spectrometry and a calibrated ionization chamber. The activity measured from different standardization methods are compatible with each other within the uncertainty limits. The CIEMAT/NIST efficiency tracing method gives the lowest uncertainty and is a reliable method for the standardization of this radionuclide.

A brief overview on radon measurements in drinking water

The aim of this paper is to present information about currently used standard and routine methods for radon analysis in drinking waters. An overview is given about the current situation and the performance of different measurement methods based on literature data. The following parameters are compared and discussed: initial sample volume and sample preparation, detection systems, minimum detectable activity, counting efficiency, interferences, measurement uncertainty, sample capacity and overall turnaround time. Moreover, the parametric levels for radon in drinking water from the different legislations and directives/guidelines on radon are presented.

90Sr determination in water samples using Čerenkov radiation

A procedure for the determination of ⁹⁰Sr in environmental water samples using Čerenkov radiation and low-level liquid scintillation counter Quantulus 1220 was applied and optimized. Low diffusion polyethylene vials, high performance glass counting vials and low potassium borosilicate glass vilas of 20 ml volume (all from PerkinElmer) were used in order to examine their potential effect on counting process. The derived efficiencies were 45.86(9)%, and a minimum detectable activity of 0.32 Bq l^-1 in a 20 ml polyethylene vial (20 ml water sample) has been achieved during 300 min of measurement. Environmental water samples might be colored and this will lead to color quenching, which one of the most important problems that affect Čerenkov is counting (Mosqueda et al., 2005). The sample channel ratio (SCR) method has been applied to correct this effect. The analytical procedures and measurement techniques were tested by participating in the IAEA-TEL-2015-03 world-wide proficiency test on determination of ⁹⁰Sr in water sample.