Ultima Gold Research Articles

Standardization of tritiated water and 204Tl by TDCR liquid scintillation counting

The triple to double coincidence ratio method was used with a combined uncertainty of 1–2% to standardize tritiated water and a solution of 204Tl. The vial with liquid scintillator, in which the sample to be measured was dissolved, is optically coupled to three photomultipliers. The electronic module MAC-3 assures the selection of double and triple coincidences count rates, D and T, from the three counting channels. It contains the gating circuits, necessary to obtain the livetime value and the extended deadtime circuit. Specific computer programs were used to calculate the free parameter value, the efficiency of D and so, the value of the activity. The optimal value of the Birks ionisation-quenching parameter, kB, was evaluated by changing the detection efficiency with grey filters. Three types of liquid scintillators, namely InstaGel ®, PPO+POPOP+Triton in toluene and Ultima Gold ®, were employed. 204Tl was measured in the frame of an international comparison organized by BIPM. For tritiated water a comparison was made with LNHB-Saclay; the relative difference between the obtained values for the massic activity was only 0.2%.

A simple method for 210Pb determination in geological samples by liquid scintillation counting

A simple procedure for the determination of 210Pb in geological samples using liquid scintillation counting is presented. Following the acid digestion of the sample, the method uses sulphate precipitation for the radiochemical separation. Finally, lead oxalate is precipitated, and once re-dissolved, it is mixed with ULTIMA GOLD AB ® scintillator cocktail. The measurement is performed using a low-level LKB Quantulus 1220™ spectrometer and the two-window technique. Calibration studies were performed to evaluate the interference of 210Bi in the 210Pb measurement. The method was tested on a geological reference sample, and gave satisfactory results and high reproducibility.

Some rules to improve the energy resolution in alpha liquid scintillation with beta rejection

Abstract Two common scintillating mixtures dedicated to alpha measurements by means of alpha liquid scintillation with pulse shape discrimination were tested: the di-isopropylnaphthalene — based and the toluene-based solvents containing the commercial cocktails Ultima Gold AB® and Alphaex®. We show the possibility to enhance the resolution up to 200% by using no-water miscible cocktails and by reducing the optical path. Under these conditions, the resolution of about 200 keV can be obtained either by the Tri CarbTM or by the PeralsTM spectrometers. The time responses, e.g., the time required for a complete energy transfer between the initial interaction alpha particle-solvent and the final fluorescence of the organic scintillator, have been compared. Both cocktails present similar behavior. According to the Förster theory, about 6-10 ns are required to complete the energy transfer. For both apparatus, the detection limits were determined for α emitters. The sensitivity of the Tri Carb was improved by 300% but remains 40% lower than that of Perals, due to a higher α/β discrimination and the use of vials with lower optical path.

Comparison and improvement of the resolution of several alpha liquid scintillation spectrometers for actinide measurements

In order to enhance the resolution in a liquid scintillation with pulse shape discrimination for the measurement of actinide at low level, a study of two scintillating cocktails (Alphaex™ and Ultima Gold LLT™) and two alpha liquid scintillation spectrometers, (PERALS™ and TRI-CARB™) was undertaken. The criteria which can be applied to improve the resolution are the use of no-water miscible cocktail, the optimisation of energy transfer through the knowledge of the spectroscopic data, the employ of P.M. with higher quantum efficiency, scintillators with low Stoke's shift and high fluorescence quantum yield and the use of vial with low optical path.

Plutonium Determination in Compacted Bentonite by Using PERALS

The determination of plutonium activities at low levels was occurred during study on diffusion of plutonium onto compacted bentonite, a candidate buffer material of multi-barrier system suggested for high-level radioactive waste disposal in Japan. It was performed by using photo/electron-rejecting alpha liquid scintillation (PERALS) spectrometry, model 8100AB (ORDELA INC.), followed by plutonium extraction from slices of the bentonite by hydrochloric acid (HC1). Pulse shape spectrum was chosen because of a high counting efficiency and only one alpha emitter existing. For an accurate determination, the optimum pulse shaped discrimination (PSD) setting was obtained. Effects resulted from HC1 concentration used for plutonium extraction and sample-loading (SL) were also investigated by PERALS spectrometry from the view of its application. The results showed that peak region in pulse shape spectrum shifted with changes of the HC1 concentrations and sample-loading. Pulse shape spectrum of background blank (liquid scintillator, Ultima Gold AB) showed an obvious peak located on the left side of alpha region. This peak influenced seriously plutonium counting by means of peak overlap when total plutonium activity in sample was less than several Bq. The low limit of detective concentration was estimated to be 0.79 Bq/g-bentonite.

234Th analysis of marine sediments via extraction chromatography and liquid scintillation counting

234Th is widely used as a natural tracer for study of biological mixing and particle scavenging processes in the ocean. This naturally occurring nuclide serves this purpose due to its convenient half-life (24.1 days), constant rate of production from 238U dissolved in seawater, and its strong tendency to attach to particles in seawater. As a beta/gamma emitter, 234Th may be determined using low-level gas-flow proportional counting, gamma spectrometry, and liquid scintillation counting (LSC). We describe here a technique which combines Cerenkov counting to evaluate 234Th (via 234Pa) with LSC alpha counting of 230Th added to the samples as a yield tracer. Our separation approach is based on a sample preparation procedure for marine sediments using nitric acid leaching in a “hot block”, and extraction chromatography (TEVA·Resin) for Th isolation. Samples are counted in plastic LSC vials, using Ultima Gold AB cocktail, in 1 M H 3PO 4 media. A series of sediment samples spiked with known amounts of 234Th yielded activities within a few percent of the anticipated values.

Determination of Low Activity of Tritium-Labeled Amino Acids Using Simultaneously Flow Scintillation and Amino Acid Analyzers

The possibility of measuring a low activity of tritium-labeled amino acids in the eluate from Amino Acid Analyzer 835 (Hitachi, Japan) using a Radiomatic 150TR Flow Scintillation Analyzer (Packard Instrument Co., USA) was studied. Due to stepped variations of pH, ionic strength, and salt concentration in eluting solutions during amino acid separation and utilization of ninhydrin reagent in spectrophotometric measurements of amino acids, special selection of scintillation liquids was necessary. Six scintillation cocktails were tested: ZhS-8 (Reakhim, Ukraine), OptiPhase “HiSafe” 3 (Wallac Oy, EGGgr; Co., Finland), Hionic-Fluor, Ultima-Flo AP, Ultima-Flo M, and Ultima Gold (Packard Instrument Co., USA). It was found that Hionic-Fluor and Ultima-Flo AP cocktails are the most appropriate for flow measurements of tritium activity. Under optimal conditions the detection limit with Hionic-Fluor and Ultima-Flo AP was 150 and 100 decays min- 1 in the peak of amino acid, respectively. Such a high sensitivity allows utilization of the above analytical system for measurements of amino acid radioactivity to study the structure of proteins and protein complexes by tritium planigraphy.

Standardization of a 89Sr solution from a BIPM intercomparison using a liquid scintillation method

A procedure to standardize 89Sr (as strontium chloride) solutions, within the frame of a BIPM intercomparison, by the CIEMAT/NIST method was presented for Instagel Plus, HiSafe III and Ultima Gold liquid scintillation cocktails. The stability was studied for two types of samples: those obtained by direct addition of the 89Sr solution and those by the extra addition of 0.5 ml of HCl (0.1 mol l −1) to the cocktails. The results only showed good stability with the three scintillants used when additional HCl was added to the cocktails. The activities per unit mass determined for 89Sr were: 26.344 kBq g −1 for Instagel Plus; 26.335 kBq g −1 for HiSafe III; and 26.310 kBq g −1 for Ultima Gold (at a reference time of 2000.10.01, 00 h UT) with a total uncertainty of 0.5% in each case ( k=1).

The solvent extraction of radium using sym-Di[4(5)-tert-butylbenzo]-16-crown-5-oxyacetic acid

The extraction of radium using sym-Di[4(5)-tert-butylbenzo]-16-crown-5-oxyacetic acid (DTBDB16C5-OAcH) in toluene is excellent. The reaction is reversible without counterions at pH higher than 9. The distribution ratio decreases as the dissolved concentration of alkaline earth ions increases. Probed factors involved in this solvent extraction system include pH values, solvents, metal ions, and the concentration of DTBDB16C5-OAcH. Liquid scintillation cocktails including Ultima Gold and Hionic Fluor were also evaluated in liquid scintillation counting.

Comparison and improvement of the determinations of actinide low activities using several alpha liquid scintillation spectrometers

We applied three procedures using two a liquid scintillation spectrometers (PERALS and TRI-CARB) and two scintillation cocktails (Alphaex and Ultima Gold LLT) for the determination of alpha-emitter low activities. For each procedure, the limit of detection, the resolution, the separation factor, and the Fischer coefficient were determined in order to perform 232U-234U-238U isotopic measurements. The deconvolution usually performed is clean when the PERALS spectrometer is used. This is not possible for the TRI-CARB spectrometer using the Ultima Gold LLT scintillation cocktail. This problem was solved by combining the advantages of both techniques using the Alphaex scintillation cocktail in the TRI-CARB spectrometer. Under these conditions, the limit of detection was improved, the resolution decreased from 500-800 to 420-590 keV, and the separation factor increased from 0.9 to 1.1-1.2. This third procedure was applied with success for 232U-234U-238U isotopic experiments.

Optimisation of liquid scintillation counting conditions for rapid tritium determination in aqueous samples

Several studies were carried out to optimise rapid tritium analysis in fresh waters by ultra-low background liquid scintillation. These included the optimisation of (1) sample/scintillant ratio, (2) pulse shape analysis, and (3) pulse-amplitude comparator, and studies concerning (1) the combination scintillant/vial and (2) the effect of chemiluminescence. The proposed method involves the mixing of 8 ml sample with 12 ml scintillation cocktail Ultima Gold AB in Zinsser low diffusion vials. These are stored during one day before counting in order to reduce chemiluminescence. The minimum detectable activity achieved was 2.2 Bq·l−1 for a total counting time of 360 minutes. In order to test the method, tritium was determined in Ebro river samples.

Development of a homogeneous pulse shape discriminating flow-cell radiation detection system

A homogeneous flow-cell radiation detection system which utilizes coincidence counting and pulse shape discrimination circuitry was assembled and tested with five commercially available liquid scintillation cocktails. Two of the cocktails, Ultima Flo (Packard) and Mono Flow 5 (National Diagnostics) have low viscosities and are intended for flow applications; and three of the cocktails, Optiphase HiSafe 3 (Wallac), Ultima Gold AB (Packard), and Ready Safe (Beckman), have higher viscosities and are intended for static applications. The low viscosity cocktails were modified with 1-methylnaphthalene to increase their capability for alpha/beta pulse shape discrimination. The sample loading and pulse shape discriminator setting were optimized to give the lowest minimum detectable concentration for alpha radiation in a 30 s count time. Of the higher viscosity cocktails, Optiphase HiSafe 3 had the lowest minimum detectable activities for alpha and beta radiation, 0.2 and 0.4 Bq/ml for 233 U and 90 Sr/ 90 Y , respectively, for a 30 s count time. The sample loading was 70% and the corresponding alpha/beta spillover was 5.5%. Of the low viscosity cocktails, Mono Flow 5 modified with 2.5% (by volume) 1-methylnaphthalene resulted in the lowest minimum detectable activities for alpha and beta radiation; 0.3 and 0.5 Bq/ml for 233 U and 90 Sr/ 90 Y , respectively, for a 30 s count time. The sample loading was 50%, and the corresponding alpha/beta spillover was 16.6%. HiSafe 3 at a 10% sample loading was used to evaluate the system under simulated flow conditions.

Application of pulse decay discrimination liquid scintillation counting for indoor radon measurement

The pulse decay discrimination (PDD) liquid scintillation technique has been applied to optimise radon counting by the Pico-Rad method. A dermination limit (with 10% relative error) of 4.8 Bqm−3 for indoor radon measurement has been achieved for optimal PDD setting with a radon elution cocktail containing 20% (v/v) of Ultima Gold AB in Instafluor. From a practical point of view this procedure allows a shortening of the counting time to 1 hour after 48 hours exposure to detectors. This method has been applied to indoor radon determinations in 626 places (municipal offices and private dwellings) in the Lodz region. These measureents resulted in an average concentration of 21.4 Bqm−3 and a median value of 15.1 Bqm−3. Analysis of the data indicates that most indoor radon comes from the underlying soil, which contains relatively little226Ra (10–20 Bqkg−1).

Study of the stability of 63Ni sources in Ultima Gold® liquid scintillation cocktail

The stability of liquid scintillation sources is an important factor for obtaining proper results in the activity measurements of radioactive samples. Some aspects of the stability of 63Ni liquid scintillation sources prepared with a commercial cocktail were investigated as a function of chemical conditions.

Role of Quenching on Alpha/Beta Separation in Liquid Scintillation Counting for Several High Capacity Cocktails

The optimization of alpha/beta separation in liquid scintillation using pulse shape analysis is convenient for the simultaneous determination of alpha and beta emitters in natural water and other samples. In this work, alpha/beta separation was studied for different scintillant/vial combinations and it was observed that both the optimum pulse shape discrimination level and the total interference value (that is, the summed relative interference between alpha and beta spectra) were dependent on the sample quenching and independent of the scintillant/vial combination. These results provide a simple method for modifying the counting configuration, such as a change in the cocktail, vial or sample characteristics, without the need to perform exhaustive parameter optimizations. Also, it was observed that, for our counting conditions, the combination of Ultima Gold AB scintillation cocktail with Zinsser low diffusion vials presented the lowest total interference, namely 0.94 ± 0.28%, which is insignificant for the counting of environmental samples.

Assessing tritium contamination on three surfaces

The performance of the wipe test using filter papers or cotton swabs was examined in order to determine recoveries of contamination on selected surfaces by low energy, β emitting radioisotopes. Filter papers or cotton swabs were saturated with Scintiverse BD, Ultima Gold, Contrad 70, dish soap, methanol, ethyl acetate, or maintained dry. Wipes were taken from Formica, stainless steel or polyurethane treated wood surfaces which were previously treated with [ 3H]triolein or [ 3H]thymidine. There were significant differences between recoveries by dry and saturated wipes. The dry wipes had poor overall recoveries which were less than 8% from any surface using either filter papers or cotton swabs. Saturated wipes had recoveries up to 50% but were significantly influenced by the saturating solution and the chemical form of the radioisotope. Cotton swabs yielded similar results when compared to filter papers for recoveries of both compounds from the three surfaces. Surface type had a significant influence on the recoveries of both compounds during the wipe test.

LSC standardization of 45Ca by the CIEMAT/NIST efficiency tracing method

A commercial solution of 45CaCl 2 and two organic compounds, 45Ca-2-ethylhexadecanoate and 45Ca-HDEHP complex, synthesized in the laboratory, have been used to produce appropriate sources for LSC measurements. A toluene-based scintillator and three commercial cocktails (Hisafe II, Ultima Gold and Instagel) were used for measuring the samples. Their concentration quenching, time stability, and spectral behaviour were studied over a 30-day period. The stable samples were used to standardize the radioactive solutions by the CIEMAT/NIST efficiency tracing method. Experimental quench curves for 3H were measured with each scintillator to cover the range of figure of merit between 1 and 4, corresponding to 3H equivalent efficiency between 52 and 12%. Experimental and computed efficiencies were in good agreement, with individual discrepancies lower than 0.6% in all cases; high efficiency values, better than 95%, were obtained with unquenched samples. A combined uncertainty of 0.4% was obtained for the activity concentration estimation of each radioactive solution.

An investigation of the various liquid scintillators used to count low-energy emitters

Radionuclidic samples were prepared ( 203Hg, 54Mn) for use with a number of commercial liquid scintillators but mainly with Packard Ultima Gold. The aim of the work was to determine the optimum composition to achieve high stability and counting efficiency for each of the radionuclides. Comparable measurements of 3H and 55Fe were also performed for samples prepared in “home made” liquid scintillators. Different fluors were used as scintillators: PPO with bis-MSB, butyl-PBD with bis-MSB, and [PFl(Pr) 2] 2. All measurements were performed using the TDCR and 4 π(LS)− γ coincidence methods.

The determination of241Pu by liquid scintillation spectrometry using the Packard 2250CA

The results of this study indicate that in terms of efficiency, the Packard 2250Ca liquid scintillation spectrometer is sensitive to the scintillation cocktail employed for241Pu analysis, particularly when the burst counting circuit is enabled. Cocktails exhibiting low t-SIE values should be avoided since quenching has a critical influence on such a low energy β− emitter. This effect would be independent of burst circuitry use. Cocktails which include naphthalene type derivatives such as the alkylnaphthalene solvent employed in Optiphase HiSafe 3 and Ultima Gold should be avoided since the broad pulse shapes produced are incompatible with the burst counting circuit which distinguishes background events from true β− events by means of pulse shape/duration analysis. Efficiency is also sensitive to the concentration of bis-MSB employed in conjunction with the primary fluor. Enhancements in efficiency are observed with appropriate concentrations. These results are in line with previous work with14C and are postulated as being a consequence of sharpening prompt pulse widths or suppression of afterpulsing. It is recommended that Instafluor should be used to maximize response, or a cocktail such as butyl-PBD/bis-MSB in pseudocumene at rates of 6 and 1.5 mg ml−1, respectively, where a lower vapor pressure solvent is particularly required.