Study on quench effects in liquid scintillation counting during tritium measurements

Quench effects can cause a serious reduction in counting efficiency for a given sample/cocktail mixture in liquid scintillation counting (LSC) experiments. This paper presents a simple experiment performed in order to test the influence of quenching on the LSC efficiency of ³H. The aim of this study was to investigate the behavior of several quench agents with different quench strengths (nitromethane, nitric acid, acetone, dimethyl-sulfoxide) added in different amounts to tritiated water in order to obtain standard sets for quench calibration curves. The OptiPhase HiSafe 2 and OptiPhase HiSafe 3 scintillation cocktails were used in this study in order to compare their quench resistance. Measurements were performed using a low-level LS counter (Wallac, Quantulus 1220).     

Beta spectra deconvolution for liquid scintillation counting

This study presents the first results of a deconvolution method for Liquid Scintillation complex spectra. The method has been developed by means of the software MATLAB and is based on the utilization of Fourier Transforms. Its main target is to obtain a fast calculation procedure capable to unfold complex spectra without requiring any preliminary knowledge of the peak shapes of the component nuclides. Experimental tests have been carried out by means of a Perkin Elmer Wallac Quantulus 1220. Distinctive features of Quantulus have not been used, the instrument was only utilized to generate spectra in numerical form that subsequently were uploaded to a PC and analyzed by MATLAB. Results show acceptable capabilities of the method both for fitting convoluted spectra and for unfolding single nuclide shapes. Further experimentation is scheduled, in order to take account of quenching effects; it will be carried out by adding to the calculation algorithm another step, capable of performing a self-choice of the number of harmonics. The final aim is to fit any kind of beta spectra also when quenching influences the shape deeply.     

Alpha-radiometry of seawater by liquid scintillation counting

Summary Liquid scintillation counting of the alpha-radionuclides after pre-concentration by cation-exchange represents a simple and robust method for the determination of total alpha-radioactivity in seawater. The total efficiency and the minimum detectable activity were calculated to be 95% and 30 mBq, respectively, for a liter sample and 1000-minute measuring time. The method has been applied successfully for the determination of alpha-radioactivity in seawater from five different coastal areas in Cyprus. The average alpha-radioactivity and uranium concentration were found to be 124±8 mBq ^. l^-1 and 3.2±0.2 mg ^. l^-1, respectively.     

Alpha-beta discrimination liquid scintillation counting for uranium and its daughters

Advances in liquid scintillation counting (LSC) technologies, such as imporved scintillation cocktail formulations and alpha-beta radiation discrimination, make LSC suitable for applications in uranium process chemistry. Ease of use, low cost, and the huge dynamic range of LSC are distinct advantages for analytical support of actinide processing. All uranium isotopes decay primarily with alpha radiation emission. The immediate short-lived daughters of²³⁸U are²³⁴Th and²³⁴Pa. These nuclides are beta emitters having energy bands that overlap the uranium bands in a liquid scintillation spectrum. The resolution of these overlapping bands by alpha-beta radiation discrimination is useful for uranium quantification and purity verification. Protactinium-234 is a high-energy beta emitter that can be further identified and quantified from it's Cherenkov radiation. Energy spectra were collected on the Packard 2500AB liquid scintillator analyzer for uranyl solutions in diisopropylnaphthalene and pseudocumene based scintillator cocktails. Calibration curves were prepared for nitric, hydrochloric, and sulfuric acid media. Base titrations demonstrated the effect of acid quenching on those system. Ion exchange and water soluble polymer extraction studies are readily followed using liquid scintillation methods.     

Radon surveys with charcoal and liquid scintillation counting

A detection system for indoor radon using vials with activated charcoal adsorbant and liquid scintillation spectrometry for measurement has been tested thoroughly for months during different seasons. Deviation in the results of two days of exposure from the mean value were at most about ±30%. This system was chosen for a pilot project for large area surveillance in Mühlviertel, a granitic area in the federal state of upper Austria. The distribution system of the detectors is described. The measurement of more than 1200 vials within about two weeks was possible by using ultra low-level liquid scintillation counters (Quantulus). The highest value observed so far was 3150 Bq/m³. Comparing the ratios of the results from the three different measurement systems (charcoal, track etch, electret) significant but acceptable differences were found not only between track etch (3 months exposure) and activated charcoal (3 days exposure), but also between track etch and electret, which both had been exposed for three months. The data are discussed regarding the dose to the population.Note: This paper reflects the personal opinions of the authors.     

An efficient inexpensive multisleeve liquid scintillation counting system

This paper reports a method that conserves greatly on the cost of counting radioactive samples for liquid scintillation counting. It accomplishes this by using several glass sleeves that are much more inexpensive than conventional counting and/or minivials, and because volumes of counting fluid are reduced the cost of the counting fluid is also markedly reduced. The usual vial system (A) uses 15 ml of counting fluid with 37% efficiency for tritum; the minivial uses .75 ml with 37% efficiency while 0.15 and 30 μl volumes gave approximately 21% efficiency. Another feature of this system is the capacity to reuse the outer sleeve(s) and dispose of the smaller counting vessel. This means that less counting fluid and glass will have to be disposed of in the environment.     

Extractive scintillators for alpha liquid scintillation counting: Anomalies in quenching evaluation

Two important effects in quenching evaluation when using some commercial extractive scintillators in alpha liquid scintillation counting are described. One affects the system quenching value but not the efficiency, while the other modifies the efficiency with no important change in the quenching. For these cocktails, alternative procedures for efficiency evaluation must be chosen. We propose an inner standard procedure which gave adequate results in the application to different kinds of samples.     

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.     

Recent progress and application of low level liquid scintillation counting

The use of an ultra low level liquid scintillation counter with extremely low background, MCA technique, storage and software evaluation of pulse height spectra has given very low LLD's, the possibility of - and -spectrometry to some extent and time saving optimization of counting conditions. Quick and very simple but yet accurate analytical methods could be worked out worked out for environmental measurements: Environmental levels of tritium,¹⁴C in several assimilation products,²²²Rn and²²⁶Ra in water without any sample pretreatment. Suggestions for possible further applications in environmenial monitoring and low level counting are given.     

Determination of131I in milk using heterogeneous liquid scintillation counting

Possibilities of the method based on both the selective separation of radioiodine from milk using anion-exchange resin as well as the¹³¹I counting in heterogeneous mixture of this anex with a liquid scintillator are presented. For samples of 4 dm³ volumes, the separation and counting efficiencies about 78% and 45% are achieved. Under the same experimental conditions the background rate is about 0.25 CPS /15 CPM/ and the LLD corresponds to about 7 mBq.dm^–3 /0.2 pCi. dm^–3/.     

Optimization of liquid scintillation counting techniques for the determination of carbon-14 in environmental samples

The goal of this work was to optimize the liquid scintillation counting techniques for the determination of¹⁴C in stack effluent gases and in environmental samples such as biological and air samples. Carbon-14 activities in most environmental samples were measured with the direct CO₂ absorption method. The highest figures of merit were found through the variation of Carbosorb E and Permafluor V ratio, and measurement windows. The best condition was an 1:1 volume ratio. Average 2.35 g of CO₂ was reproducibly absorbed in the 20 ml mixture within 40 minutes. The counting efficiency determined by repeated analysis of NIST oxalic acid standard and the background count rate were measured to be 58.8±1.4% and 1.88±0.06 cpm, respectively, in case of saturated solution. The correction curves of counting efficiency for partially saturated solutions and for saturated solutions with quenching were prepared, respectively. The overall uncertainty of the sample specific activity for near background levels was estimated to be about 7% for 4 hours counting at 95% confidence level. Stack effluent gas samples were measured by a gel suspension counting method. After precipitation of CO₂ in the form of BaCO₃, 140 mg of which was mixed with 6 ml H₂O and 12 ml of Instagel XF. The counting efficiency was measured to be 71.5±1.7% and the typical sensitivity of this technique was about 510 mBq/m³ for a 100 min count at a background count rate of 4.7 cpm. For the benzene counting method measurements were performed with a mixture of 3 ml benzene and 1 ml of scintillation cocktail (5 g of butyl-PBD in 100 ml of scintillation-grade toluene) in a low potassium 7 ml borosilicate glass vial. The counting efficiency and the background count rate were measured to be 64.3±1.0% and 0.51±0.05 cpm, respectively. The long-term stability of samples has been checked for all the counting techniques over a two week period, during which no apparent change in counting efficiency and background level was found.     

Development of a method for the determination of 226Ra by liquid scintillation counting

Liquid scintillation counting has not been widely applied to a-particle detection because of its poor energy resolution and variable background. In the present work, a time saving and reasonably accurate method for determination of ²²⁶Ra in water has been developed, using liquid scintillation spectrometry and pulse-shape analysis. The effect of three levels of chemical quench on the spillover of alpha interactions into the beta window and vice versa was assessed. The advantages of liquid scintillation in comparison with other methods (radon emanation) for determination of ²²⁶Ra are the high counting efficiency (~100%) and the easier sample preparation, with no need for sample preconcentration.     

Gross alpha/beta analyses in water by liquid scintillation counting

Summary The standard procedure for analyzing gross alpha and gross beta in water is evaporation of the sample and radioactivity determination of the resultant solids by proportional counting. This technique lacks precision, and lacks sensitivity for samples with high total dissolved solids. Additionally, the analytical results are dependent on the choice of radionuclide calibration standard and the sample matrix. Direct analysis by liquid scintillation counting has the advantages of high counting efficiencies and minimal sample preparation time. However, due to the small sample aliquants used for analysis, long count times are necessary to reach required detection limits. The procedure proposed consists of evaporating a sample aliquant to dryness, dissolving the resultant solids in a small volume of dilute acid, followed by liquid scintillation counting to determine radioactivity. This procedure can handle sample aliquants containing up to 500 mg of dissolved solids. Various acids, scintillation cocktail mixtures, instrument discriminator settings, and regions of interest (ROI) were evaluated to determine optimum counting conditions. Precision is improved and matrix effects are reduced as compared to proportional counting. Tests indicate that this is a viable alternative to proportional counting for gross alpha and gross beta analyses of water samples.     

Improved method for the determination of the cortisol production rate using high-performance liquid chromatography and liquid scintillation counting

Two new methods for the determination of the cortisol production rate using reversed-phase high-performance liquid chromatography are described. One uses ultraviolet detection at 205 nm, the other on-line post-column derivatization with benzamidine, followed by fluorimetric detection. The specific activity of tetrahydrocortisol and tetrahydrocortisone in urine from patients who had received tritium-labelled cortisol was determined by the indicated methods, followed by fraction collection and liquid scintillation counting. The post-column reaction detection procedure was superior to ultraviolet detection, both in selectivity and analysis time. Intra- and inter-assay variance of the post-column reaction detection procedure were 3.7 and 4.7%, respectively. A good correlation (r = 0.99) was obtained between values determined by this procedure and by a thin-layer chromatographic procedure.     

Automatic sample preparation of35S labelled organic compounds for liquid scintillation counting

An automatic sample preparation method for the determination of³⁵S in organic compounds by liquid scintillation counting is described. The sample is burned in a stream of oxygen and the combustion products are led onto a quartz wool column wetted with dilute hydrogen peroxide. Sulfur oxides are retained on the quartz wool as sulfuric acid, while the other acid producing combustion products are eliminated by evaporation. The residual sulfuric acid in rinsed with distilled water, the sulfuric acid solution obtained is added to a liquid scintillation cocktail and the radioactivity is measured with a liquid scintillation counter. The combustion-evaporation process runs automatically according to the operational program carried out by an electronic programmer.     

210Pb and its progenies in phosphoric acid: Significance for low level determinations using liquid scintillation counting with extractive cocktails

When measuring²¹⁰Pb via its progenies using the extractive cocktail Polex^TM, the sample must be transferred to a phosphate system. When measuring low level samples, care has to be taken in the choise of the phosphoric acid used, as it may contain rather large amounts of²¹⁰Pb. Typical activity concentrations for products of different manufacturers are given.     

Radionuclides analysis in hot spring waters in Korea by liquid scintillation counting

Tritium and ¹⁴C concentration in hot spring water in Korea were determined. Tritium in the most hot spring samples could not detected and concentration range was <0.5?C1.31?TU. And ¹⁴C contents were ranged 1.7?C78.6?pMC. From the ³H and ¹⁴C analysis, we found some hot springs are mixed with recent groundwater and hot spring water ages were estimated from 1,940 to 32,800?years. And also, ²²⁶Ra and ²²⁸Ra were determined simultaneously in hot spring water, and some other radionuclides were also analyzed. Content distribution of ²²²Rn was 50?C3,760?pCi/L, ²²⁶Ra was <0.003?C0.15?Bq/L and ²²⁸Ra was below the detection limit.