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

Strontium-90 (⁹⁰Sr) 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 ⁹⁰Sr 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 collected from an area of riverbed affected by a ⁹⁰Sr groundwater plume. Sixteen samples, plus spike and water blanks, were analyzed. Five different measurements were performed to determine the ⁹⁰Sr and yttrium-90 (⁹⁰Y) activities in the samples: direct triple-to-double-coincidence ratio (TDCR) Cherenkov counting of ⁹⁰Y, liquid scintillation (LS) counting for ⁹⁰Sr following radiochemical separation, LS counting for ⁹⁰Y following radiochemical separation, Cherenkov counting for ⁹⁰Y following radiochemical separation and LS counting of the Sr samples for ⁹⁰Y in-growth. The counting was done using a low-level Hidex 300SL TDCR counter. Each measurement method was compared for accuracy, sensitivity and efficiency. The results following Cherenkov counting and radiochemical separation were in very good agreement with one another.     

Rapid determination of radiostrontium in seawater samples

A new method for the determination of radiostrontium in seawater samples has been developed at the Savannah River National Laboratory (SRNL) that allows rapid pre-concentration and separation of strontium and yttrium isotopes in seawater samples for measurement. The new SRNL method employs a novel and effective pre-concentration step that utilizes a blend of calcium phosphate with iron hydroxide to collect both strontium and yttrium rapidly from the seawater matrix with enhanced chemical yields. The pre-concentration steps, in combination with rapid Sr Resin and DGA Resin cartridge separation options using vacuum box technology, allow seawater samples up to 10 L to be analyzed. The total ⁸⁹Sr + ⁹⁰Sr activity may be determined by gas flow proportional counting and recounted after ingrowth of ⁹⁰Y to differentiate ⁸⁹Sr from ⁹⁰Sr. Gas flow proportional counting provides a lower method detection limit than liquid scintillation or Cerenkov counting and allows simultaneous counting of samples. Simultaneous counting allows for longer count times and lower method detection limits without handling very large aliquots of seawater. Seawater samples up to 6 L may be analyzed using Sr Resin for ⁸⁹Sr and ⁹⁰Sr with a minimum detectable activity (MDA) of 1–10 mBq/L, depending on count times. Seawater samples up to 10 L may be analyzed for ⁹⁰Sr using a DGA Resin method via collection and purification of ⁹⁰Y only. If ⁸⁹Sr and other fission products are present, then ⁹¹Y (beta energy 1.55 MeV, 58.5 day half-life) is also likely to be present. ⁹¹Y interferes with attempts to collect ⁹⁰Y directly from the seawater sample without initial purification of Sr isotopes first and ⁹⁰Y ingrowth. The DGA Resin option can be used to determine ⁹⁰Sr, and if ⁹¹Y is also present, an ingrowth option with using DGA Resin again to collect ⁹⁰Y can be performed. An MDA for ⁹⁰Sr of <1 mBq/L for an 8 h count may be obtained using 10 L seawater sample aliquots.     

The simple radiochemical determination of 90Sr in environmental solid samples by solvent extraction

Determination of ⁹⁰Sr in environmental solid samples is a challenging task because of the presence of so many other radionuclides in samples of interest. This problem was dealt with by radiochemical separation of strontium followed by yttrium separation and Cerenkov counting of the high-energy ??-particle emissions of ⁹⁰Y in order to quantitate ⁹⁰Sr. In this work, an improved method is described for the determination of ⁹⁰Sr in soil samples, through the separation of the daughter ⁹⁰Y at equilibrium. The procedure is based on the HDEHP solvent extraction in combination with liquid scintillation spectrometry (LSS). A low background Quantulus has been optimized for low level counting of Cerenkov radiation emitted by the hard ??-emitter ⁹⁰Y. The analytical quality of the method has been checked by analyzing IAEA Soil-375 reference materials. The analytical method has also been successfully applied to the determination of ⁹⁰Sr for moss-soil samples in inter-laboratory exercises through IAEA??s ALMERA network. The chemical recovery for ⁹⁰Y extraction ranged from 80 to 85% and the counting efficiency was 73% in the window 25?C400 keV.     

A sensitive method based on HDEHP extraction and LSS for the determination of 90Sr in solid samples

An improved and rapid method is described for the determination of ⁹⁰Sr in environmental samples, through the separation of the daughter ⁹⁰Y at equilibrium. The procedure is based on the HDEHP solvent extraction in combination with liquid scintillation spectrometry (LSS). A low background QuantulusÔ has been optimized for low level counting of Cerenkov radiation emitted by the hard b-emitter ⁹⁰Y. The counting efficiency was 60% and the background 0.53 cpm. The reliability and reproducibility of the method have been checked using IAEA reference materials. The chemical recovery for ⁹⁰Y extraction ranges from 83 to 90%.     

Rapid and accurate determination of89/90Sr in radioactive samples by Cerenkov counting

An improved and rapid method for determination of⁹⁰Sr via its daughter nuclide,⁹⁰Y, in aqueous samples from the low-level radioactive wastes by Cerenkov counting was established. This technique is applicable to beta particles maximum energies greater than 0.263 MeV in aqueous solution. A comparison of⁹⁰Sr determination by Cerenkov counting and standard wet chemical separation techniques indicates a high degree of correlation and excellent agreement. For a 20 ml aqueous sample following the prescribed experimental conditions and a 60 min counting interval, the detection limit was 0.20 dpm/ml (0.10 pCi/ml), and the relative deviation is less then 5%.     

A rapid method for determining strontium-90 in urine samples

Rapid bioassay methods for ⁹⁰Sr in urine samples are needed to provide an early estimation of possible internal dose resulting from exposure to radiostrontium in the event of a radiological and nuclear emergency. In this work, a fast column separation method followed by liquid scintillation counting for detection of ⁹⁰Sr in urine was developed. Replicate spike and blank samples were analyzed for performance evaluation of the method. Using this method, a detection limit of ~10 Bq L^?1 for ⁹⁰Sr can be achieved with a sample analysis turn-around time of 4 h for a set of 12 samples. The method is adequate to meet the radiobioassay acceptance criteria and is suitable for quick dose assessment of ⁹⁰Sr exposure following a radiation emergency.     

Determination of <Superscript>90</Superscript>Sr in preparedness: Optimization of total analysis time for multiple samples

In radiological emergency, rapid determination of radiostrontium will be necessary. The required quantification levels will be relatively high which offers smaller sample sizes and shorter ingrowth and counting times. In this paper a rapid method for the determination of ⁹⁰Sr in fresh milk in emergency preparedness is presented. The method is based on microwave digestion, chemical separation of Sr, ingrowth of ⁹⁰Y and Cherenkov measurements. In order to minimize the total analysis time, a mathematical model was developed. For a given number of samples the model minimizes the analysis time by optimizing the ingrowth and counting time in order to reach a detection limit fit-for-purpose.     

A rapid method for the determination of strontium-90 in powdered milk

A method in which⁹⁰Y the daughter product of⁹⁰Sr decay is extracted by tributyl phosphate (TBP) from ashed powdered milk is described. The⁹⁰Y which is in equilibrium with⁹⁰Sr is back-extracted into the aqueous phase and coprecipitated with milligram amounts of ferric hydroxide. The proposed procedure makes it possible to obtain thin planar sources convenient for low level gas counters. The overall detection efficiency of 45.5% for⁹⁰Y (including chemical recovery of yttrium) was achieved. The detection limit for 200 g powdered milk samples and 10 000 s counting time was 0.065 Bq·kg^–1. The concentration of⁹⁰Sr in three-year old samples (after Chernobyl accident) ranged from 0.81 to 1.31 Bq·kg^–1.     

Development of rapid solvent extraction based radioanalytical technique for estimation of 90Sr in the presence of natural and anthropogenic radionuclides

A radiochemical technique for estimation of ⁹⁰Sr concentration by direct extraction of ⁹⁰Y with bis (2-ethylhexyl) phosphate (HDEHP) in toluene was developed and standardized. About 90% ⁹⁰Sr retained in the aqueous phase at the optimized pH 4–4.5. Cerenkov counting with 0.04 g mL⁻¹ sodium salicylate as a wavelength shifter resulted in 7.5 fold increase its Cerenkov counting efficiency. The method was validated by estimating ⁹⁰Sr in certified reference materials like, IAEA TEL 2016-03 drinking water, Spruce needle and IAEA-156 Clover. The interference of naturally occurring Ra and its β progeny especially Pb was eliminated by means of Cerenkov counting. Conventional radiochemical separation was used to compare ⁹⁰Sr activity in effluent samples.

     

Enzymatic degradation of large vegetation samples for the simultaneous determination of129I,actinides and strontium

A radiochemical procedure is given for the simultaneous determination of low levels of¹²⁹I, actinides (Pu, Am, Cm) and⁹⁰Sr in vegetation samples. It is shown that grass samples up to 5 kg fresh weight can be wet ashed conveniently by hydrogen peroxide under alkaline conditions, subsequent to an initial enzymatic disintegration. After purification of the iodine fraction,¹²⁹I is determined by neutron activation analysis. Using alpha spectrometry,²³⁸Pu and^239,240Pu are determined in the plutonium fraction, and²⁴¹Am,²⁴²Cm, and²⁴⁴Cm in the americium/curium fraction. The⁹⁰Sr is determined after separation by beta counting its decay product⁹⁰Y.     

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.     

Feasibility study of an analytical method for detecting <Superscript>90</Superscript>Sr in soil using DGA resin and Sr resin

This study investigated an analytical method for detecting ⁹⁰Sr in soil samples for the routine monitoring of environmental radioactivity. Mineral acid leaching and fusion methods were first used to digest the soil sample, and the analytical results were compared. DGA resin was employed to separate ⁹⁰Y, being a daughter of ⁹⁰Sr. Then, ⁹⁰Y was analyzed by liquid scintillation counter (LSC). These analytical results were compared with those obtained using Sr resin, which is a well-known, simple and reliable separation method. With the DGA resin approach a minimum detectable activity of ~0.28 Bq kg^?1 was detected in a 50 g sample, with 180 min of counting time, 70% recovery and ~97% counting efficiency using a LSC.     

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.     

Possible overestimation of the external standard quench parameter on Wallac 1220 Quantulus™ with high energetic beta-emitters

The 1220 Quantulus is equipped with an ¹⁵²Eu external source used to determine an external standard quench parameter SQP(E). The relationship between ⁹⁰Sr/⁹⁰Y counting efficiency and SQP(E) was found linear in a defined range of SQP(E) values. This function was fixed after many counting experiences made with ⁹⁰Sr/⁹⁰Y standards. The sasme equation is used for the measurement of ⁹⁰Sr in environmental samples. The first goal of this paper is to objectify an overestimation of the SQP(E) when high energetic beta-emitters like ⁹⁰Y are present (1 to 4% in routine conditions). The second one is to show how this artefact could induce a bias in the calculation of ⁹⁰Sr activity in environmental samples. The median of this overestimation is estimated around 6%. Another approach using ⁸⁵Sr standard is suggested to avoid this overestimation. Provided the chemical composition — and thus the quenching — is similar for the two standards, the counting efficiency measured with the ⁹⁰Sr/⁹⁰Y standard could be related to the SQP(E) value of the ⁸⁵Sr standard. Indeed this one appears to be more robust regarding to the range of activity and to the counting time of the external source.     

Polymer-coated magnetic nanoparticles for rapid bioassay of <Superscript>90</Superscript>Sr in human urine samples

A rapid bioassay for ⁹⁰Sr was developed involving preconcentration of ⁹⁰Sr/⁹⁰Y from human urine samples with a cation exchange polymer (poly–acrylamido–methyl–propanesulfonic acid) coated onto magnetic nanoparticles, followed by selective elution of ⁹⁰Sr (over ⁹⁰Y) with phosphate for determination by liquid scintillation analysis. The minimum detectable activity for this method (4.9 ± 0.5 Bq/L) is lower than the required sensitivity of 19 Bq/L for ⁹⁰Sr in human urine samples, as defined in the requirements for radiation emergency bioassay techniques for the public and first responders based on the dose threshold for possible medical attention recommended by the International Commission on Radiological Protection. The relative bias was 9.2%, the relative precision was 3.2%, and the linear dynamic range covered 12–600 Bq/L. This simple and rapid bioassay method is found to be in compliance with the HPS ANSI N13.30 performance criteria for radiobioassay.     

Improved method for the separation of radioactive strontium from various samples by mixed solvent anion exchange

Procedures for the separation and determination of⁹⁰Sr in liquid samples, with cation and anion exchangers have been described. Strontium, yttrium and other cations bind to the cation exchanger and are eluted from the column by means of nitric acid. Separation of yttrium and strontium from other cations is carried out on columns filled with strong base anion exchangers in nitrate form with alcoholic solutions of nitric acid. This separation method enables the determination of⁹⁰Sr through yttrium on a low-level gas flow α, β-counter, as well as through strontium on a lowlevel liquid scintillation counter by means of Cherenkov counting. Such procedures have been tested by the determination of⁹⁰Sr in water, wine, medium radioactive liquid waste samples, milk and clover samples. For comparison, the determination has also been carried out by the standard method. It has been showed that the developed procedures might produce a high efficiency in strontium separation and a satisfactory accuracy of determination.     

Radioactive accumulation in alga samples from Romanian Black Sea coast

The natural and artificial radioactivity of the brown algaCystoseira barbata samples collected on the Romanian Black Sea coast in 1996 is reported. The results on¹³⁷Cs were obtained through gamma-spectrometry, on⁹⁰Sr by beta-counting of the⁹⁰Y oxalate precipitated after strontium separation, on²²⁶Ra by the emanation method, while the concentrations of U, Th, Pu and Am isotopes were obtained through radiochemical separations using tracers followed by alpha-spectrometry counting of the stainless steel discs after electrodeposition. These results add further evidence thatCystoseira barbata may be used as a bioindicator for radioactive contamination of the coastal waters.     

Measurement of (90)Sr in environmental samples by cation-exchange and liquid scintillation counting

A new method for the measurement of (90)Sr in environmental samples by cation-exchange and liquid scintillation counting is described. Strontium carbonate is purified by precipitation and ion-exchange, weighed for the determination of chemical yield, dissolved in hydrochloric acid and mixed with the liquid scintillator, Aquasol-2. Two channels of a low-background liquid scintillation counter are used to determine (90)Sr, (90)Y and (89)Sr, free from the effects of environmental tritium. The values of (90)Sr obtained by this method are in good agreement with those from ordinary (90)Y milking and the gas proportional counting method. The concentration of (90)Sr in the air at Tokai-mura in Japan has been measured by the new method.     

Studies on soil samples mineralization conditions preceding the determination of 90Sr

Some results of the extraction of strontium and yttrium from soil samples by concentrated nitric acid are described. The concentration of Sr and Y in the solid was determined by XRF method. The results obtained allowed to elaborate the conditions of acid leaching and to propose an analytical procedure for the determination of ⁹⁰Sr in samples without their total dissolution.     

Seasonal variations of atmospheric210Pb and7Be concentrations at Kumamoto, Japan and their removal from the atmosphere as wet and dry depositions</p> </p>

Summary A relatively simple chemical separation procedure has been developed for the simultaneous determination of⁸⁹Sr and ⁹ 0Sractivities in water samples and on aerosol-filters of the Nuclear Power Plant (NPP) Paks origin. The procedure combines the cation-exchange chromatographic (Dowex 50 WX 8 resin) and solid phase extraction (EIChroM Sr.Spec?, DC18C6 crown ether) steps. The beta-radiation of radionuclides can be measured directly after the chemical separation by LSC. The activities of⁸⁹Sr,⁹⁰Sr and⁹⁰Y are calculated from an over determined set of equations using a method of constrained optimization technique. The equations are based on LSC measurements performed in three counting windows plus the⁹⁰Sr-⁹⁰Y decay law. The chemical yield of strontium is determined by ICP-AES. The lowest limits of detectable activity, for the measurement time of 600 minutes, are 30 mBq/sample and 18 mBq/sample for⁸⁹Sr and⁹⁰Sr, respectively.