Cherenkov Counting Research Articles

Adaptation of PTB’s analytical modelling for TDCR–Cherenkov activity measurements at LNHB

Designed for triple to double coincidence ratio measurements based on liquid scintillation, the three-photomultipliers detection system can also be applied for Cherenkov counting using aqueous solutions. For activity determination, a specific modelling of Cherenkov light emission has to be constructed. For that purpose, the analytical modelling first developed at PTB was adapted to account for the physical features of the detection system used at LNHB. The first results are presented in the case of activity measurements of two high-energy β−-emitters (90Y and 89Sr). The analytical modelling was also tested for the standardization of 68Ge in a solution of 68Ge/68Ga in equilibrium in the framework of a BIPM international comparison in 2014.

Determination of radionuclidic impurities in 99mTc eluate from 99Mo/99mTc generator for quality control

Technetium-99m is the principal radioisotope used in medical diagnostics; radionuclidic impurity is the major concern of its quality. This work presents a analytical method for sequential determination of all radionuclidic impurities listed in pharmacopoeia including gamma emitters, alpha emitters, 89Sr and 90Sr. Radioactive decay for removal of 99mTc, ion exchange and extraction chromatography for removal of 99Mo and 99Tc are effective for separation of interferences. Gamma spectrometry, LSC with alpha/beta discrimination, and Cherenkov counting using LSC are sensitive methods for measurement of the impurity radionuclides. The detection limits of this method are well meet the requirement of the quality control according to the limitation of the pharmacopoeia.

Standardization of 68Ge/68Ga using the 4πβ−γ coincidence method based on Cherenkov counting

In the framework of an international BIPM comparison (Bureau International des Poids et Mesures), the activity standardization of 68Ge in a solution of 68Ge/68Ga in equilibrium provided by NIST was carried out at LNHB. This exercise was organized to meet the growing interest in 68Ga as a radiopharmaceutical in nuclear medicine services (e.g. as a surrogate of 18F for PET imaging). Due to the volatility of germanium, the activity standardization of 68Ge was investigated at LNHB by means of 4πβ−γ coincidence counting based on Cherenkov measurements. This technique was applied to take advantage of the Cherenkov threshold (~ 260keV in aqueous solutions) in order to prevent counting from electron-capture events associated with 68Ge disintegrations. Cherenkov counting was performed using glass and polyethylene vials and the resulting activity concentrations were compared with 4πβ−γ coincidence measurements based on liquid scintillation. The efficiency-extrapolation curve obtained with Cherenkov measurements in glass vials was compared to Monte Carlo simulations based on the Geant4 code.

A radionuclide calibrator based on Cherenkov counting for activity measurements of high-energy pure β¯-emitters

Due to their stability and reproducibility, re-entrant pressurized ionization chambers (also called radionuclide calibrators) are widely used for activity measurements in nuclear medicine services as well as in national metrology institutes to maintain reference standards. Generally, these secondary instruments yield accurate activity measurements for γ-emitting radionuclides. Ionization chambers are easy to use and thus well-adapted to guarantee the metrological traceability between national metrology institutes and end-users. However, the reproducibility of calibration factors can be significantly impaired when measuring high-energy pure β¯-emitters such as radiopharmaceuticals based on 90Y. This is because the bremsstrahlung emission contributing to the instrument response is strongly dependent on the geometry of the components surrounding the radioactive solution. The present article describes a new design based on pulse counting to address this problem. It takes advantage of Cherenkov emission resulting from Compton scattering in transparent materials. The interest of Cherenkov counting is to obtain a low-sensitivity detector that enables direct measurements of high-activity solutions (at least up to 10 GBq for 90Y-microspheres in aqueous suspensions used in nuclear medicine). A simple design based on a geometry close to an ionization chamber used at LNHB (Vinten 671 type) is described. The feasibility in terms of detection efficiencies (lower than 10−4 for 90Y solutions) of the new radionuclide calibrator is investigated by Monte Carlo calculations using the Geant4 code.

The effect of counting conditions on pure beta emitter determination by Cherenkov counting

The Cherenkov counting efficiencies measured by three commercially available liquid scintillation counters, Triathler, Tri-Carb 3180, Hidex 300 SL were compared. The influences of energy of pure beta emitters, volume, and solvent as well as instrument type on Cherenkov counting efficiency were studied. The best Cherenkov counting efficiencies are on the Hidex 300 SL and when methanol is used as a solvent. It could be concluded that the sensitivities of low-level versions of Tri-Carb and Hidex 300 SL are comparable. Based on the overall results obtained it has been concluded that the TDCR Cherenkov counting is well suited for routine quantitative determination of low activities of high energetic beta emitters.

Method for rapid screening analysis of Sr-90 in edible plant samples collected near Fukushima, Japan

A screening method for measuring 90Sr in edible plant samples by focusing on 90Y in equilibrium with 90Sr is reported. 90Y was extracted from samples with acid, co-precipitated with iron hydroxide, and precipitated with oxalic acid. The dissolved oxalate precipitate was loaded on an extraction chromatography resin, and the 90Y-enriched eluate was analyzed by Cherenkov counting with a TDCR liquid scintillation counter. 90Sr (90Y) concentration was determined in plant samples collected near the damaged Fukushima Daiichi Nuclear Power Plants with this method.

Primary standardization of SIR-Spheres based on the dissolution of the 90Y-labeled resin microspheres

The project “Metrology for molecular radiotherapy” is a collaborative European project initiated to bring together expertize in ionizing radiation metrology and nuclear medicine research. This project deals with the development of personalized dosimetry to individual patients who are undergoing molecular radiotherapy (also known as targeted radionuclide therapy). The general aim is to provide a metrological traceability to primary standards for individual dosimetry in the case of molecular radiotherapy. In particular, one objective is the standardization of 90Y-labeled resin microspheres SIR-Spheres (Sirtex, Sydney, Australia) used for the treatment of liver cancer by radioembolization. The present paper describes the primary measurements carried out using the Triple to Double Coincidence Ratio (TDCR) method applied after the complete dissolution of the SIR-Spheres in the Sirtex vial. A method for the dissolution was developed to optimize the homogeneity of the solution to enable the primary measurements based on Cherenkov and liquid scintillation counting. A comprehensive description of the protocol implemented for the microsphere dissolution is reported. First calibration factors obtained with the reference ionization chambers at LNE-LNHB are also given.

Determination of 90Sr via Cherenkov counting and modified Eichrom methods in bilberry matrix in the context of BIPM supplementary comparison

Quantitative determination of 90Sr in bilberry, a representative matrix for vegetables and fruits, by Cherenkov counting and modified Eichrom methods is presented. The compatibility of the two methods was checked through the measurement of the BIPM supplementary comparison bilberry sample (CCR(II)-S8). The activity concentration of 90Sr in bilberry sample was measured as 153 ± 4 and 152 ± 7 Bq kg−1 by Cherenkov counting and modified Eichrom method, respectively which is in good agreement with the reference value, 153 ± 8 Bq kg−1.

Semi-automated procedure for the determination of 89,90Sr in environmental samples by Cherenkov counting

The paper describes semi-automated procedure for determination of 89,90Sr in drinking water. It includes quantitative capture of 89,90Sr on SuperLig 620 column from large volume of water samples and their on-column detection via Cherenkov counting on liquid scintillation counter. In this case, SuperLig 620 column acts as a specific strontium separator and a sensor for Cherenkov counting. The method enables determination of 89Sr and 90Sr above 30 mBq L−1 with good accuracy within 64 h.

Cherenkov counting of 90Sr and 90Y in bark and leaf samples collected around Fukushima Daiichi Nuclear Power Plant

The radioactivity of 90Sr and 137Cs in environmental samples, bark and leaf, collected around the Fukushima Daiichi Nuclear Power Plant in May 2013 was determined with the aim of investigating the migration of both nuclides using their radioactivity ratio. The radioactivity of 90Sr was determined by using Cherenkov counting of 90Y after purification using Sr resin and that of 137Cs was determined by γ-spectrometry. Quench correction in Cherenkov counting was investigated by measurements of samples spiked with purified 90Y revealed that the radioactivity could be evaluated without quench correction. The radioactivity ratio of 90Sr to 137Cs in bark samples of 4.2 × 10−3 and 1.2 × 10−2 was compared with the results from soil samples collected in July 2011 to show that the migration of 90Sr was slower than 137Cs in bark and tree.

Handling interferences in 89Sr and 90Sr measurements of reactor coolant water: A method based on strontium separation chemistry

Measurements for determining the activity of 89Sr and 90Sr in reactor coolant water are associated with limitations due to interferences from radionuclides with similar chemical properties and β−-energies. From a measurement bias point-of-view these interferences would result mainly in an overestimated activity concentration of 90Sr.In order to address the interference problem, a common and well-known method was used in order to show the need for sufficient decontamination. An improvement was achieved by taking the sample through two initial strontium separations in order to increase the decontamination factor. This method determines the activity concentration of 89Sr and 90Sr, via its daughter nuclide 90Y, by Cherenkov counting. This work is primarily based on theoretical calculations of strontium-, yttrium- and other potential interfering radionuclide ratios after instant fission. The work done to confirm the theoretical calculations were carried through on spiked strontium standard solutions and fresh reactor coolant water. The reactor coolant water was known to contain interferences at a composition resembling that of instant fission. The detection limit for double separation was calculated to 0.17Bq/kg for 90Sr and 0.38Bq/kg for 89Sr. When using methods that solely rely on strontium resins, this paper shows that the decontamination factor (DF) is significantly higher when using double separation than that of a single separation. The paper also shows that the DF of an initial double strontium separation is as effective when it comes to removing high ratio interferences as separations done with both Sr- and Ln-resin (EiChrom Technologies, Inc., 2003; Tovedal et al., 2009b). However, ‘old’ samples, where e.g. 140Ba and 89Sr has decayed, does not benefit from double separation. Furthermore, samples with low ratios of interfering radionuclides does not benefit from using this method either, seeing as this is a more time consuming method due to the double separations.

Rapid determination of 90Sr/90Y in water samples by liquid scintillation and Cherenkov counting

Strontium-90 ( 90 Sr) is a ubiquitous contaminant at nuclear facilities, found at high concentrations in spent nuclear fuel and radioactive waste. Due to its long half-life and ability to be transported in groundwater, an accurate method for measuring 90 Sr in water samples is critical to the monitoring program of any nuclear facility. To address this need, a rapid procedure for sequential separation of Sr/ Y was developed and tested in groundwater samples col- lected from an area of riverbed affected by a 90 Sr groundwater plume. Sixteen samples, plus spike and water blanks, were analyzed. Five different measurements were performed to determine the 90 Sr and yttrium-90 ( 90 Y) activities in the samples: direct triple-to-double-coin- cidence ratio (TDCR) Cherenkov counting of 90 Y, liquid scintillation (LS) counting for 90 Sr following radiochemi- cal separation, LS counting for 90 Y following radiochem- ical separation, Cherenkov counting for 90 Y following radiochemical separation and LS counting of the Sr sam- ples for 90 Y in-growth. The counting was done using a low- level Hidex 300SL TDCR counter. Each measurement method was compared for accuracy, sensitivity and effi- ciency. The results following Cherenkov counting and radiochemical separation were in very good agreement with one another.

Evaluation of interferences on measurements of 90Sr/90Y by TDCR Cherenkov counting technique

A study to evaluate conditions affecting the determination of 90Sr/90Y activities in liquid samples by the triple-to-double coincidence ratio (TDCR) Cherenkov counting technique was conducted. The Cherenkov radiation produced by the 90Y beta decay was determined using a commercially available Hidex 300 SL liquid scintillation counter. The interferences of sample geometry, including sample counting vial type and volume composition, and sample colour on the TDCR were investigated. The effects of potentially interfering beta and mixed beta–gamma emitters on the TDCR Cherenkov counting of 90Sr/90Y activities were also examined. The TDCR values were used to quantify counting efficiencies of 90Y under different experimental conditions. The results demonstrated that the Cherenkov counting efficiency of 90Y is independent of sample volume and counting vial size. The effect of colour quenching was examined using yellow and brown food-grade dyes. The TDCR correction for colour quenching was found to be effective. An evaluation of counting efficiency of different beta-emitting radionuclides demonstrated that strong gamma emissions can contribute to the Cherenkov counting efficiency. Overall, measured radioactivity values deviated from reference values by ≤7.5 %, which is acceptable for screening applications in emergency situations.

Determination of 90Sr in radioactive concentrate from Nuclear Power Plant Mochovce

This paper describes the use of molecular recognition technology product AnaLig®Sr-01 gel from IBC Advanced Technologies, Inc. to effectively and selectively pre-concentrate, separate and recover strontium from evaporator concentrate samples from Nuclear Power Plant Mochovce which belongs to the most difficult matrices to analyze. The method is suitable for analyzing highly contaminated samples of radioactive waste in a relatively short time and with high decontamination factors. Activity of 90Sr was measured using Cherenkov counting on TRI CARB 2900 TR liquid scintillation counter.

Fast determination of 90Sr/90Y activity in milk by Cherenkov counting

Cherenkov counting of the 90Sr/90Y pure beta emitters is an attractive method for 90Sr activity determination, but the color quenching effect may be significant, especially for strongly colored or semi-opaque media. A quench correction method based on the external source of some liquid scintillation systems (named ESAR – external source area ratio) was proposed and checked for aqueous solutions and was proved to be effective also for urine samples. In the present work, the application of the ESAR method for fast determination of 90Sr/90Y activity in milk samples is described.

Determination of 90Sr–90Y activity in urine samples by using Cherenkov counting

Cherenkov counting of the 90Sr–90Y pure beta emitters in aqueous samples is an attractive method; but color quenching correction is needed, this being especially significant for urine which is characterized by a strong coloration. A quench correction method based on the external source of some liquid scintillation systems (named ESAR—External Source Area Ratio) was proposed for aqueous solutions. In the present work, the application of the ESAR method for determination of 90Sr–90Y in human urine samples is described.

Continuous separation of Sr, Y and some actinides by mixed solvent anion exchange and determination of 89,90Sr, 238,239Pu and 241Am in soil and vegetation samples

Methodology for the determination of 89,90Sr, Am and Pu isotopes in complex samples is given. Methodology is based on simultaneous isolation of Sr, Y and actinides from samples by mixed solvent anion exchange chromatography, mutual separation of 89,90Sr and 90Y from actinides, mutual separation of Th, Pu and Am by extraction chromatography, quantitative determination of 89,90Sr by Cherenkov counting and quantitative determination of Pu and Am isotopes in soil and vegetation samples by alpha spectrometry. It is shown that Y and Sr can be efficiently separated from alkaline, alkaline earth and transition elements as well as from lanthanides and actinides on the column filed by strong base anion exchanger in nitrate form and 0.25 M HNO3 in mixture of ethanol and methanol as eluent. It is also shown that Pu, Am and Th strongly binds on the mentioned column, can be separated from number of elements and easily be eluted from column by water. After elution actinides were mutually separated on TRU column and electrodeposited on stainless steel disc. Examination of conditions of electrodeposition was shown that chloride-oxalate electrolyte with addition of DTPA in presence of sodium hydrogen sulphate in cell with cooling and rotating platinum anode enables deposition of actinides within 1 h by 0.8 A cm−2 current density. Obtained peaks FWHM for Pu, Am and Th isotopes are between 27 and 40 keV. Scanning electron microscopy picture and ED XRF analysis of electroplated discs showed that actinide deposition is followed by iron oxide formation on disc surface. The methodology was tested by determination of 89,90Sr, Am and Pu isotopes in ERA proficiency testing samples (low level activity samples). Obtained results shows that 89,90Sr, 241Am and 238,239Pu can be simultaneously separated on anion exchange column, 89,90Sr can be determined by Cherenkov counting with a satisfactory accuracy and limit of determination within 1–3 days after separation. 241Am and 238,239Pu can easily be separated on TRU column and determined after electrodeposition with acceptable accuracy within 1 day.

Rapid determination of 89,90Sr in wide range of activity concentration by combination of yttrium, strontium separation and Cherenkov counting

The methodology for the rapid determination of 89,90Sr in wide range of activity concentration is given. Methodology is based on simultaneous separation of strontium and yttrium from samples by mixed solvent anion exchange chromatography, mutual separation of 89,90Sr from 90Y by hydroxide precipitation and quantitative 89,90Sr determination by Cherenkov counting within 3 days. It is shown that Y and Sr can be efficiently separated from alkaline, alkaline earth and transition elements as well as from lanthanides and actinides on the column filed by strong base anion exchanger in nitrate form and 0.25 M HNO3 in mixture of ethanol and methanol as eluent. Decontamination factor for Ba, La and other examined elements except calcium is low and can not affect quantitative determination in predictable circumstances. Methodology for quantitative determination by Cherenkov counting based on following the changes of sample activity over time is described and discussed. It has been shown that 89,90Sr can be determined with acceptable accuracy when 89Sr/90Sr ratio is over 10:1 and that separation of Y enables reliable determination of 89Sr and 90Sr in wide range of 89Sr/90Sr ratios (60:1) and in some cases in presence of other yttrium and strontium isotopes. The methodology was tested by determination of 89,90Sr in Analytics crosscheck samples (nuclear waste sample) and ERA proficiency testing samples (low level activity samples). Obtained results shows that by using of low level liquid scintillation counter it can be possible to determine 89Sr and 90Sr in wide range of concentration activity (1–1,000 Bq/L/kg) with uncertainty below 10% within 2–3 days. Results also show that accuracy of determination of 89Sr (and 90Sr) strongly depends on the determination of difference between separation and counting time when activity ratio of 89Sr/90Sr is high. Examination the influence of media and vial type on background radiation and counting efficiency has shown that lowest limit of determination can be obtained by using of HNO3 in plastic vials as counting media, because in this combination figure of merit is maximized. For the recovery of 50% and 100 min of counting time estimated MDA is 55 Bq and 90 Bq for 90Sr and 89Sr, respectively. Analysis of combined uncertainty shows that it mainly depends on uncertainty of efficiency and recovery determination, uncertainty of activities determination for both isotopes and level of background radiation.

Application of low-level beta counting of 32Si for the measurement of silica production rates in aquatic environments

Silicon is an important element for certain plankton groups in aquatic systems. In marine systems there is a strong coupling between the biogeochemical cycles of carbon and nitrogen with that of silicon due to the high proportion of primary productivity carried out by diatoms. Currently 32Si is the most used radiotracer for the measurement of biogenic silica production rates in aquatic systems with isotope activity typically quantified by Cherenkov or liquid scintillation counting. Here we describe a new method for quantifying 32Si activity using a gas-flow proportional counter optimized for low-level beta radiation analysis. The background activity is two-orders of magnitude lower and more stable than that of liquid scintillation counters, leading to consumption of 67–75% less isotope per sample. Sample preparation is non-destructive enabling reanalysis of samples indefinitely. Methods for counting samples under conditions of secular equilibrium and non-equilibrium between 32Si and its daughter isotope 32P are described. Analysis of equilibrated samples yields the highest sensitivity and accuracy, but requires that sample analysis be delayed for 120 days for secular equilibrium. Non-equilibrium methods are less accurate, but provide results within 2 days enabling experimental designs and protocols to be evaluated and optimized in near real time.

Separation of Sr in combination of ion exchange and Sr resin with alcohol-nitric acid solution and rapid determination of 90Sr in wine and soil samples

This paper describes the procedures of isolating strontium from wine and soil samples which enable creating of procedure for rapid determination of 90Sr. The method of determination of 90Sr includes binding of Sr on the cationic exchanger IR-120 from the sample and simultaneous elution from the cation column and binding on the Sr column, separation of Sr on Sr resin with HNO3 even in presence of alcohols and subsequent Cherenkov counting. Sr can be efficiently bind on Sr resin and separated from the other elements with lower acid concentrations in the presence of a low portion of alcohol, or even from a wine sample without the loss of Sr resin capacity. The binding strength of Sr on Sr resin decreases with the rising of HNO3 concentration (1–5 M) in the presence of 13% of ethanol or methanol, and with the rising of the alcohol portion in constant concentration of HNO3. Application of cation exchanger for Sr binding in phase of sample preparation decreases Sr column loading and improve Sr recovery. The method allows the determination of 90Sr activities in wine and soil sample lower than 10 mBq in reasonable time.