Ultima Gold Research Articles

Application of portable liquid scintillation counter for on-field measurement of tritium in aqueous samples during radiation emergency

Screening of aqueous samples for 3H contamination is required to decide suitability of water intended for human consumption during radiation emergency. BARC, Trombay has recently procured Portable Triathler liquid scintillation counter as a screening tool for on-site response to radiation emergency. For this purpose, parameters like, different available scintillators, scintillator to sample ratio and influence of different capacity scintillation vials were optimized for 3H concentration measurement. The study indicated that for 7 mL vials, the optimized scintillator to sample ratio was 4:1 for Optiphase Hisafe II, Ultima Gold Ultra Low Level Tritium, Aqualight AB and Dioxane based scintillators whereas for Ultima Gold AB and Optiphase Hisafe III scintillators it was 3:1. In case of 20 mL vials, the ratio was optimized to 8:1 for all the above mentioned six scintillators. Additionally, the effect of applying counting efficiency using calibration curves generated using distilled water and that obtained using optimized scintillator to sample ratio in various spiked water samples was also studied. Results in 3H concentration (2000–5700 Bq/mL) indicate about ±10% deviation using both the methods for commercially available scintillators. However, in case of Dioxane based scintillator, the deviation was higher (20%). For analysis of 3H concentration ∼200 Bq/mL using commercially available scintillators results in higher deviation of about 21% due to unreliable quench indicating parameter for count rate less than 4000. The study indicated that calibration curves constructed using optimized parameters are universally applicable for determination of 3H concentration in wide variety of water samples.

Characterization of a water-based liquid scintillator for use in megavoltage radiotherapy beams

The measurement of the dose delivered in radiotherapy treatments is carried out using dosimeters that are often expensive to produce and sometimes toxic to humans and the environment, which leads to more complex and rigorous clinical manipulations. It is in this context that it is necessary to provide new types of scintillators that would no longer have these problems while having properties equivalent to those of human tissues. Thus, the following study presents the performance of a water-based liquid scintillator used at radiotherapy energies. The characteristics studied include the proportionality of the scintillation signal to the dose, the scintillation efficiency at two different energies as well as the identification of the Cherenkov portion of the signal for photon beams of 180 kVp, 6 MV as well as 18 MV. Spectral measurements of the scintillation solution and a solution of distilled water were acquired in order to isolate the contribution of the scintillation signal from the spectrum obtained, and then compared to a commercial scintillator, Ultima Gold. The signal exhibits a linear dose relationship with a correlation coefficient of 0.999 and lower scintillation efficiency than Ultima Gold.

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.

Permeability and diffusion of tritium in bentonite

Abstract. As a part of the Croatian RD&D (research, development, and demonstration) program within the Program for LILW (low- and intermediate-level waste) and SNF (spent nuclear fuel) disposal, research of permeability and the diffusion of tritium in bentonite was organized, as part of the research of the future engineering barriers for repositories of LILW and SNF. Two types of materials were prepared, namely pure sodium bentonite and a mixture of sodium bentonite (12 %) with quartz sand (88 %). Compaction of materials was conducted with a modified Proctor test, and the apparatus was designed and made at the Faculty of Mining, Geology and Petroleum Engineering at the University of Zagreb, utilizing fused deposition modeling 3D printer and PETG (polyethylene terephthalate glycol) material. Water enriched with 3H has been prepared by dilution of the National Institute of Standards and Technology (NIST) 3H standard (4926e) to 6 L. The activity of the prepared enriched water was 49 700±180 TU. One part of the device was filled with 3H-free water and the other with 3H-spiked water (0.6 L volume for each part). In total, five devices with bentonite and five devices with a sand–bentonite mixture were prepared this way. The devices were thoroughly sealed to avoid loss of sample and isotopic exchange with the atmosphere and put horizontally in holders. The water for 3H activity measurements was sampled monthly or bimonthly. A total of 8 mL of the sample was taken by syringe and transferred to a measurement vial. Each vial was additionally filled with 12 mL of a scintillator (Ultima Gold LLT, PerkinElmer) and thoroughly mixed. 3H activity was determined by a liquid scintillation counter (LSC; Quantulus 1220) at the Laboratory for Low-level Radioactivities, Ruđer Bošković Institute, Zagreb. Due to the penetration of bentonite from the barrier into the water samples, tritium-free water has relatively high activity after 2 months of the experiment (average value was 5560±240 TU). In the final sampling, after a 2-month time span, the activity reached 9670±2490 TU. Later, sampling and measurement were not possible due to the high bentonite amount within the samples. Tritium-free samples from the sand–bentonite mixture device were stable, and the first analyses (1 month after the experiment setup) showed an average activity of 533±31 TU, while the final (5-month time span from the first sampling) average activity was 12 800±3430 TU. The increase in the concentration from the beginning to the end of the experiment was almost exponential. Spiked samples from the bentonite device had an average activity of 36 950±2550 TU at the first sampling and 17 580±13 320 TU after a 1-month time leg. Later, sampling was not possible. Spiked samples from sand–bentonite mixture showed a decrease in tritium activity from the first sampling (43 390±1310 TU) to 27 210±285 TU (5 months after the first sampling). Considering the penetration of bentonite material into the water samples, only the sand–bentonite mixture can be considered for further analyses through the calculation of the diffusion.

PERFORMANCE EVALUATION OF COMMERCIAL SCINTILLATION COCKTAILS FOR LOW-LEVEL TRITIUM COUNTING BY HIGH-CAPACITY LIQUID SCINTILLATION COUNTER.

Low-background liquid scintillation counter is one of the popular measuring instruments used to investigate tritium radioactivity in environmental media. These instruments require the liquid sample and organic solvent to be mixed for tritium measurement. In the European Union, the registration, evaluation, authorization and restriction of chemicals regulation was established to control the use of chemical substances of very high concern. It is important to find continuously available alternative reagents. In this paper, a performance evaluation was conducted using four scintillation cocktails according to Japanese conventional procedure; although one of them, Gold Star LT2, contains nonylphenol ethoxylate, it will continue to be available for research and development. From the evaluation results it was confirmed that Gold Star LT2 would be a satisfactory alternative scintillator, which is similar performance of Ultima Gold LLT.

Preliminarily Experiments of Liquid Scintillation Cocktail Waste Solidification

Liquid scintillation spectroscopy (LSC) is a widely used laboratory method for measuring radioactive especially low-energy alpha and beta emitter isotopes in solutions. Since the scintillation cocktails (SCs) contain large amounts of aromatic hydrocarbon compounds after the LSC measurement, the sample usually becomes organic radioactive waste, which is challenging to manage and dispose of. The most common and effective waste treatment method is incineration, a costly and cumbersome solution. Another simpler and less expensive way is the immobilization the organic liquids by embedding in cement or geopolymer matrix.The aim of our experiments is to find a universal mix design to solidify and immobilize scintillation cocktail wastes (SCWs) of unknown composition. During the measurement, we assumed that the SCWs could contain Ultima Gold, Ultima Gold LLT, InstaGel Plus and ProSafe FC type scintillation cocktails in pure form or mixed with unknown quantities of water. Therefore, we performed experiments with inactive pure SCs as surrogates to mimic the SCWs. Since the water content determination of the organic solutions is difficult, the mix design must be independent of the water content of SCWs.During our experiments, we found an appropriate mix design to solidify all available SCs up to 5% using CEM I 42.5 N type cement, Metaver N type metakaolin and sodium hydroxide. We could solidify our tested SCW with this mix, and this product meets the waste acceptance criteria of all Hungarian radioactive waste repositories.

Novel technique for simultaneous detecting three naturally occurring radon isotopes (222Rn, 220Rn and 219Rn)

Radon inspection is becoming increasingly prevalent due to its negative effects on human health. After cigarette smoking, radon is the second leading cause of lung cancer due to its internal dosage through respiration. In this study, we employed a novel liquid scintillation technique to simultaneously detect three naturally occurring radon isotopes (222Rn, 220Rn and 219Rn). The detection method utilises the delayed coincidence technique and the pulse shape discrimination implemented by digital charge comparison. Furthermore, a Monte Carlo simulation was performed to obtain the gamma response functions of the detector using standard 22Na, 60Co and 137Cs gamma sources. Additionally, the detector resolution and energy calibration parameters were determined by comparing the measured and simulated light output distributions. For the measurement, radon gas from the atmosphere was infused into 700 mL of Ultima Gold AB for 48 h. We determined that the minimum detectable activities of 222Rn (238U decay chain), 220Rn (232 Th day chain) and 219Rn (235U decay chain) were 1.7, 1.0 and 1.2 mBq/l, respectively. The proposed novel technique offers a potential application for detecting all three naturally occurring radon isotopes in water samples.

Occurrence of 222Rn and 226,228Ra in underground water and 222Rn in soil and their mutual correlations for underground water supplies in southern Greater Poland

European Union Council Directive 2013/51/EURATOM recently sets out so-called indicator parameters for: radon, tritium and indicative dose of water intended for human consumption. The aim of this research was to elaborate an effective procedure for determination of radon and radium 226,228Ra isotopes (which are potentially the main contributors to the internal dose from drinking and cooking water) and to find the possible relationships between these radionuclides in underground water reservoirs and 222Rn concentration in the soil gas in their vicinity. The research was performed by applying a non-volatile and water-immiscible scintillation cocktail based on a pure diisopropylnaphthalene (Ultima Gold F: UGF), which allow for efficient radon extraction from 0.5 dm3 of water samples to 20 cm3 of scintillation phase and its direct determination with a detection limit of 5 × 10–3 Bq dm−3. The further preliminary concentration of 3 dm3 of crude water samples by evaporation to 0.5 dm3 samples led to the removal of all unsupported 222Rn activity and allowed the 226Ra determination via equivalent 222Rn detection after one-month samples storage using a low-background Triathler liquid scintillation counter in the α/β separation counting mode. Together with determination of 226Ra isotope in water samples, the simultaneous measurements of 228Ra and 222Rn radionuclides concentrations in water as well as 222Rn activity in the soil gas around the water supply sites were performed. The achieved limit of 226Ra detection was at a very low level of 10–3 Bq dm−3. The measured values of 226Ra concentration in 50 public underground water supply units for the Kalisz district of Poland were relatively low and ranged from below detection limit to 28.5 × 10–3 Bq dm−3 with arithmetic mean and median values of 12.9 and 12.2 × 10–3 Bq dm−3, respectively. Weak correlations were observed between activity concentrations of 226Ra and 222Rn in the crude water samples (R2 = 0.31) and 222Rn in water and its concentration in the nearby soil gas (R2 = 0.48).

In quest of the optimal coincidence resolving time in TDCR LSC

This paper presents studies of the influence of the coincidence resolving time on the activity calculated by the Triple-to-Double Coincidences Ratio (TDCR) method in Liquid Scintillation (LS) counting. Recently, published methods for the correction for accidental coincidences in TDCR counting open the possibility to use resolving times up to several μs, long enough not to miss true coincidences and to study the effects of delayed fluorescence.3H, 14C, 55Fe and 63Ni LS-sources in UltimaGold (UG), UG LLT and Toluene+PPO cocktails were measured using a TDCR counter connected to a digitizer working in list-mode. The necessary resolving time to include 99.9% of the logical sum of double (D) coincidences was found to be 1.2 μs for 3H, 1 μs for 55Fe and 500 ns for 63Ni in UG. The activity of all LS-sources was calculated using the TDCR method for resolving times from 10 ns to 2 μs and a significant dependence between the calculated activity and resolving time was observed. A dedicated Monte Carlo (MC) code was used to simulate list-mode data from TDCR measurements. The simulation results suggest that the 3H activity calculated by the TDCR method is overestimated regardless of the used resolving time if delayed fluorescence is present which is not described by the used ionization quenching function.Efficiency variation measurements of 3H in UG LLT show a strong dependence of the optimal kB parameter on the used resolving time: 85 μm/MeV at 40 ns and 110 μm/MeV at 200 ns, leading to 2.5% difference in calculated activity. In the framework of this study the efficiency variation methods by chemical quenching and gray filters were compared and a difference of 60 μm/MeV between the two was observed. The results from this article demonstrate that regardless of the available corrections for accidental coincidences, it is not advisable to increase the resolving time beyond what is necessary to register all prompt fluorescence events. Moreover, even for short coincidence resolving times, delayed fluorescence could have a significant influence on the activities calculated by the TDCR method.

Application of a liquid scintillation system with 100-ml counting vials for environmental tritium determination: Procedure optimization, performance test, and uncertainty analysis

For more efficient and accurate determination of airborne tritium in the environment, the procedure optimization, performance test and uncertainty analysis of a commercially available low-background liquid scintillation counting (LSC) system with 100-ml counting vials were studied in this work. The results showed that 50 ml water sample mixed with 50 ml scintillation cocktail (Ultima Gold uLLT, PE) could achieve the optimal counting condition after a dark adaption time longer than 1440 min. The minimum detectable activity (MDA) of the 100-ml vial system was estimated to be 0.18 Bq·L−1 in a continuous counting time of 3600 min, which was approximately 3.5 times lower than that of 20-ml vial system, and its determination uncertainty was also generally lower provided the collected samples was more than 15 ml. It indicates that the LSC system with 100-ml counting vials is preferable for environmental tritium determination. However, for more accurate determination, the electrolytic enrichment is still needed for the sample with the specific activity lower than 0.4 Bq·L−1. On the other hand, considering the cost and potential environmental impact of present available cocktails, the system with 20-ml vials is recommended for determining the sample with the specific activity higher than 2 Bq·L−1.

Applicability of a 100-mL Polyethylene Vial for Low-Level Tritium Measurement Using a Low-Background Liquid Scintillation Counter

For low-level tritium measurements using a liquid scintillation counter, scintillation vial selection is important. The applicability of polyethylene (PE) vials was studied. Three types of vials were tested: (1) 100-mL perfluoroalkoxy alkane (PFA) fluorine resin vials, (2) 100-mL PE vials, and (3) 145-mL PE vials. Ultima Gold LLT was the reference liquid scintillator in this study. The background counts for these vials were found to be 2.5 counts per minute. Tritiated water of 1.5 Bq‧mL−1 was employed as an internal standard to determine the counting efficiency. The counting efficiencies for the 100-mL PFA, 100-mL PE, and 145-mL PE vials were estimated to be 17%, 16%, and 13%, respectively. The lower limits of detection of these vials for a counting time of 100 min were 1.45 Bq‧L−1 for 100-mL PFA vials, 1.54 Bq‧L−1 for 100-mL PE vials, and 1.47 Bq‧L−1 for 145-mL PE vials. Thus, these vials demonstrate similar performances for tritium measurements.

Dosimetric properties of colloidal quantum dot-based systems for scintillation dosimetry

Colloidal quantum dots (cQDs) are starting to be used in radiation detection, either combined with an organic fluorophore or used as a sole luminescent material. In the latter case, only few studies report on cQD-based detectors for medical applications, especially for scintillation dosimetry in radiation therapy. Moreover, most of these studies focus on the effects of radiation on cQD photoluminescence but do not look into the properties of the scintillation signal itself. The present article provides a study of those cQD scintillation properties not previously investigated including the linearity of the signal as a function of dose, the signal dose rate and beam energy dependencies. The latter was also characterized for the commercially available scintillating fiber BCF-60 and liquid scintillator Ultima Gold. CdSe multishell cQDs in two physical forms were used as a sensitive dosimeter volume: a cQD powder to constitute a fiber optic based dosimeter and cQD liquid dispersions to be volumetric dosimeters. The signal linearity was assessed with a R2 coefficient >0.999 over a clinically relevant dose range at kV and MV beam energies. The cQDs had a good overall dose rate independence, with a change from the relative dose of 1% at MV energies and 2% at kV energies, of their scintillation output when irradiated with an orthovoltage device and a linear accelerator. Regarding the beam energy dependence, the cQD powder had the highest dependence amongst all the scintillators compared, the 120 kVp light output being up to almost 4 times that of the 6 MV beam. The smallest effect of the beam energy was reported for the cQD alkylbenzene liquid dispersion, having a variation of light signal normalized to 6 MV of 15% that is even less than for BCF-60 and Ultima Gold.

Application of liquid scintillators as energy conversion materials in nuclear batteries

The application of liquid scintillators as energy conversion materials in nuclear batteries was proposed. By introducing liquid scintillators, the output properties of radioluminescence (RL) nuclear batteries based on different liquid scintillators were investigated via low-energy X-ray. Results indicated that the values of short circuit current Isc and maximum output power Pmax increased as the X-ray intensity increased, and the output power of nuclear battery with Ultima Gold liquid scintillator was greater than those of batteries with Emulsifier-Safe or Bioscint liquid scintillator under excitation condition of 25 kV tube voltage. To analyze the RL effects of the liquid scintillators under X-ray excitation, we measured the RL spectra of the different liquid scintillators. Considering luminescence utilization in batteries, the surface of the quartz cuvette was covered with Al film. Al is a high-performance reflective material that can increase the scintillation light released by Ultima Gold, reaching the GaInP/GaAs/Ge device. After covering a thin Al film, the output power of the battery was significantly improved under X-ray excitation.

222Rn Determination in Water and Brine Samples Us-ing Liquid Scintillation Spectrometry

Liquid scintillation spectrometry (LSC) is the most common technique used for 222 Rn determination in environmental aqueous sample. In this study, the performance of water-miscible (Ultima Gold AB) and immiscible (Optiscint) liquid scintillation cocktails has been compared for different matrices. 241 Am, 90 Sr and 226 Ra standard solutions were used for LSC calibration. 214 Po region was defined as better for both cocktails. Counting efficiency of 76 % and optimum PSA level of 95 for Ultima Gold AB cocktail, and counting efficiency of 82 % and optimum PSA level of 85 for Optiscint cocktail were obtained. Both cocktails showed similar results when applied for 222 Rn activity determination in water and brine samples. However the Optiscint is recommended due to its quenching resistance. Limit of detection of 0.08 and 0.06 Bq l − 1 were obtained for water samples using a sample:cocktail ratio of 10:12 mL for Ultima Gold AB and Optiscint cocktails, respectively. Limit of detection of 0.08 and 0.04 Bq l − 1 were obtained for brine samples using a sample:cocktail ratio of 8:12 mL for Ultima Gold AB and Optiscint cocktails, respectively.

Investigation of fast screening LSC method for monitoring 14C activity in wastewater samples

This paper explores the possibility of a direct measurement of 14C activity concentration in wastewater without chemical pretreatment of samples, which would provide the advantages such as rapidity, low-cost, and simplicity of radioanalysis that is desirable in the case of nuclear emergencies. A method via Liquid Scintillation Counting (LSC) technique has been implemented and optimized. The method assumes mixing of the water sample with a scintillation cocktail (Permafluor E+ and Ultima Gold AB cocktails were tested). Measurements were performed on Ultra Low Level Liquid Scintillation Spectrometer Wallac 1220 Quantulus. Optimization of the method included optimal water:cocktail volume ratio, optimal counting window selection, PAC (Pulse Amplitude Comparator) parameter adjustment, based on the highest FOM (Figure of Merit) value achieved, as well as detection efficiency and detection limit evaluation. The main problem in such an approach, interference with other beta emitters that are often present in wastewater samples, has been discussed. The possibility to eliminate low-energy counts that would be generated from 3H, and to estimate the contribution of other high-energy beta emitters to obtained results of 14C content is presented as well. Method's constraints, its accuracy, and precision have been considered from the obtained results of measurements of wastewater samples. Its application is limited only to 14C screening of samples with much higher 14C activities than those of the environmental (surface and ground) waters. Presented results could be used as guiding principles of development, optimization, and implementation of the fast 14C screening method in other laboratories.

Evaluation of different LSC methods for 222Rn determination in waters

Monitoring of 222Rn in drinking or surface waters, as well as in groundwater has been performed regularly in connection with geological, hydrogeological and hydrological surveys and health hazard studies. Liquid scintillation counting (LSC) is often preferred analytical method for 222Rn measurements in waters as it allows multiple-sample automatic analysis. LSC method implies mixing of water samples with organic scintillation cocktail, which triggers radon diffusion from the aqueous into an organic phase for which it has a much greater affinity, eliminating the possibility of radon emanation in that manner.The main aim of this paper is calibration of the liquid scintillation counter Qunatulus 1220™ for measuring of radon in water and evaluation of two different methods (one-phase and two-phase) in order to obtain the most suitable LSC technique for radon in water measurement. In this study four different scintillation cocktails were tested: one miscible (Ultima Gold AB) and three immiscible (High Efficiency Mineral Oil Scintillator, Opti-Fluor O and Ultima Gold F). Evaluation of presented methods was based on obtained detection efficiency and achieved Minimal Detectable Activity (MDA) values. Comparison of presented methods, accuracy and precision, as well as different scintillation cocktail's performance, was considered from results of measurements of 226Ra spiked water samples with known activity and environmental samples. LSC results were compared with the results of radon in water measurement obtained by alpha spectrometer RAD7. Calibration was done as a dependence of calibration factor (CF) from Pulse Shape Analysis (PSA).According to the obtained results, with proper adjustment of calibration parameters, both methods could be used for radon in water measurements. The obtained MDA values for all four scintillation cocktails are very low, less than 0.1 Bq l−1 for measuring time of 300 min.

Characterization of a binary system composed of luminescent quantum dots for liquid scintillation

Scintillation dosimetry has evolved towards utilizing 3D liquid dosimeters to perform quality assurance verification of complex treatment configuration for photon, electron and proton beams. However, most of the fluorophores utilized in these dosimeters are alike and present limitations. This study aims to establish the profile of CdSe colloidal quantum dots (cQDs) that were given the role of the fluorophore in a binary liquid scintillation system. We chose to investigate the cQDs because of their wide absorption spectrum, the tunability of their absorption and emission spectra with respect to their size and composition, and their ability to function as an effective energy transfer intermediate. The scintillation intensity and spectral response of three organic solvent-based liquid cQD dispersions have been investigated upon irradiation with kV and MV photon beams. The solvents used to disperse the cQDs were hexane, toluene and linear alkylbenzene. The scintillation efficiency of the cQD dispersions has proven to be dependent on the nature of the solvent, the alkylbenzene cQD liquid dispersion having the brightest light emission of the three solutions, for an equivalent deposited dose in the scintillator. Its light output was found to reach a tenth of the light intensity of a commercial liquid scintillator, Ultima Gold, irradiated under the same conditions. This cQD dispersion also demonstrated a remarkable energy transfer to the cQDs, only 5% of its intensity being due to Cherenkov light production in the solvent. Overall, these results indicate that the alkylbenzene cQD liquid dispersion could be the best choice for a potential cQD-based liquid scintillator.

Bilateral comparison of 14C activity measurements at the NCBJ RC POLATOM and the ENEA-INMRI

A bilateral comparison of 14C activity measurements between ENEA-INMRI (Italy) and NCBJ RC POLATOM (Poland) was organized in the year 2015 and piloted by POLATOM, which provided the sources for the comparison. A set of six sources in Ultima Gold scintillator was measured at POLATOM using four different counters by two liquid scintillation counting methods: TDCR and CIEMAT/NIST. Three of sources were measured also at ENEA-INMRI by using two different TDCR counters. The results achieved in the comparison show an excellent agreement.

Determination of 129I using volatilization method and liquid scintillation spectrometry

A simple and rapid separation method for 129I determination in radioactive waste samples was developed. Suitable conditions for iodine volatilization were tested. Iodine was trapped in 1.5 mol L−1 NaOH and precipitated as PdI2·H2O by addition of PdCl2 with recoveries higher than 80%. The method was applied for analysis of contaminated soil, radioactive sludge, evaporator concentrate and heterogeneous waste samples from nuclear power plants in Slovak Republic. 129I was measured on liquid scintillation counter TRI CARB 2900 TR using Ultima Gold AB scintillation cocktail.

On the stability of 3H and 63Ni Ultima Gold liquid scintillation sources

The stability of 3H and 63Ni samples, made with Ultima Gold and Ultima Gold AB using eight aqueous fractions ranging between 0.1% and 10%, was monitored over a period of 32 weeks. Counting rate losses were measured in all cases, but were found to be particularly severe for samples with low aqueous fractions. Hydrodynamic diameter measurements of the reverse micelles of 3H and 63Ni in Ultima Gold and Ultima Gold AB samples were performed with dynamic light scattering. For Ultima Gold, the micelle diameters were measured to be about 2nm and slightly dependent of the aqueous fraction, while for Ultima Gold AB they were found to vary strongly with the aqueous fraction and range between 1 and 4nm. The hypothesis that the counting rate instabilities derive from changes in the sizes of micelles was tested by measuring them four times over the monitoring period. The measurement results do not support this claim.