The problem of adsorption on silicagel in a liquid scintillation radiometry of14C labelled compounds

By means of liquid scintillation spectrometry we investigated the counting efficiency of the samples containing toluene solution of scintillator (PPO, butyl-PBD, PT) and 1-methyl[2−¹⁴C]imidazolidinone-2 adsorbed on the silicagel, depending on concentration of scintillator, mass of radioactive compound, and mass of another nonactive compound introduced to samples as an impurity. For the sake of comparison the efficiency of counting homogeneous samples and the ones with Ba¹⁴CO₃ deposit was determined. It was found, that the efficiency of detection of a radioactive compound adsorbed on the silicagel is conditioned by composition of adsorptive layer on the support surface.     

Simultaneous determination of35S and14C in double-labelled organic compounds by liquid scintillation counting

An isotope analytical method for the simultaneous determination of³⁵S and¹⁴C in double-labelled organic compounds by liquid scintillation counting is described. The sample is burned in a stream of oxygen. Sulfur oxides are converted to sulfuric acid and separated from other combustion products, including carbon-14 dioxide, on a heated quartz wool column previously wetted with hydrogen peroxide. Carbon dioxide is collected from the gas stream by an absorbent suitable for liquid scintillation counting. The residual sulfuric acid is rinsed off the column with water and the aqueous solution obtained is mixed with a liquid scintillation cocktail for radioactivity measurement. The final solutions ready for counting are obtained in less than fifteen minutes, quantitative collection recovery is achieved and no cross contamination occurs.     

A novel method for the simultaneous determination of125I and14C activities using liquid scintillation counting

The viability of a dual label liquid scintillation technique has been investigated. To avoid the need for two procedures, gamma counting for¹²⁵Iodine (¹²⁵I) and liquid scintillation counting for¹⁴C. Since the¹²⁵I spectrum covers almost as wide a range of pulse heights as¹⁴C, conventional dual label methods would result in very low¹⁴C counting efficiencies. The conventional dual label technique has ben modified to increase the¹⁴C counting efficiency and to accomodate the consequent additional spillover of¹²⁵I counts into the upper window. This dual label technique has been applied to the determination of¹²⁵I and¹⁴C activities in blood samples. The accuracy of the method has been tested, and its advantages and limitations are discussed.     

Radon determination by activated charcoal adsorption and liquid scintillation measurement

A passive diffusion method for the determination of radon concentration has been optimised and calibrated. The device consists of a scintillation vial containing activated charcoal, a diffusion barrier and a desiccant agent. The response to diverse atmospheric humidity and variable exposure intervals was studied. The result is a detector independent of atmospheric humidity till 7 days of exposure. The method was compared with electret detectors (US EPA) with very satisfactory results. The advantages of this method are its simplicity, low cost, low detection limit, the total automatization of the measurement and its total independence of humidity to measure in a wide range of radon concentrations.     

Alpha liquid scintillation measurement of plutonium in solution spiked by236Pu

The liquid-liquid extraction method used with alpha liquid scintillation with rejection of -emission is strongly dependent of the nature of the aqueous solution containing actinides. We propose to measure plutonium quantitatively by its labelling with²³⁶Pu. Two procedures of quantitative extraction have been developed as well as the mathematical fit to obtain accurate results. The limits of detection have been determined for several counting times like for instance 0.2 pg/l after one day of acquisition time. We have applied both procedures successfully for the determination of plutonium in doped drinking water and in solid samples after dissolution.     

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.     

Problem of adsorption on silica gel in the liquid scintillation radiometry of14C labelled compounds. Deviation from channel ratio curve

Dependence of counting efficiency of 1-methyl [2-¹⁴C]-imidazolidinone-2 adsorbed on the surface of various silica gels (different grain size and pore diameter) on scintillator (PT, PPO, butyl-PBD) concentration in three scintillation solvents was investigated by means of liquid scintillation spectrometry. It was established that the reason for deviations of the experimental points from the standard channel ratio curve is scintillation heterogeneity of the measured system. Proposition of an additional mechanism for excitation energy transport straight from silica gel globules to adsorbed molecules of the scintillator is discussed.     

Application of the double ratio technique to emulsion systems for liquid scintillation counting of3H and14C labelled materials

Emulsion counting, more correctly known as colloid counting, is the most widely practised technique for the radioassay of aqueous sample types by the liquid scintillation technique. The double ratio technique can be used to determine whether or not radioactivity is being counted with true solution efficiency, and was applied to a range of systems consisting of deionised water, Triton X-100 and toluene (containing³H-water,³H-toluene or¹⁴C-toluene). Some hypotheses were developed in an attempt to explain the double ratio values obtained for the various systems studied.     

The measurement of222Rn in drinking water by low-level liquid scintillation counting

Radon-222 (Rn) has universally been found in well water. Non-stagnant ground water is collected at the well head while the well is pumping. The water is adjusted to a slow, non-aerated, steady flow through a clear tube, and a 500 ml glass bottle is filled. The sample is tightly capped after a high meniscus has developed. In the laboratory, standard 22 ml glass vials are filled with 10 ml of a toluene based mineral oil LS cocktail. Then, two 5 ml sample aliquots are pipetted into the vial. Vials are capped tightly, shaken vigorously, and placed in the liquid scintillation (LS) counter. Secular equilibrium is established in approximately 4 hours, after which samples are counted for 100 minutes each. The counting efficiency for Rn and progeny ranges between 315 to 345 percent depending on the chosen spectral window. The average background is about 6 cpm. A total of 28 wells were tested for Rn in the Carefree-Cave Creek, Arizona, USA area. The area's geometric average Rn concentration was found to be 46.5 Bq·l^–1. The associated estimated lung dose is 0.51 mSv·y^–1.Deceased 1 June 1991.     

Removal of the impurities from environmental water samples for tritium measurement by liquid scintillation counting

Liquid scintillation counting is the most popular method for tritium measurement, however, it takes much time and a lot of doing to distill off the impurities before mixing the sample water and liquid scintillation cocktail. We have investigated the possibility of an alternative method to the distillation. We have found out that the filtration can be an alternative to distillation for the environmental water samples before electrolytic enrichment.     

Evaluation of a direct extraction/liquid scintillation counting technique for the measurement of uranium in water

An extraction procedure utilizing alpha liquid scintillation was evaluated for the rapid determination of uranium in aqueous environmental samples. The extraction efficiency of the system was measured under varying chemical conditions including pH. The procedure was evaluated against a traditional radiochemical technique using both laboratory prepared control samples and actual groundwater. Finally, the possibility of obtaining isotopic information from the liquid scintillation spectra was also investigated using a curve fitting routine.     

Rapid measurement of 241Pu activity at environmental levels using low-level liquid scintillation analysis

A straightforward and rapid method has been developed for the determination of ²⁴¹Pu activities. Pu is chemically separated from the sample, purified and electrodeposited to produce a source for alpha spectrometric determination of ²³⁸Pu and ^239,240Pu. Pu is stripped from the disc with concentrated nitric acid and extracted into tri-octylphosphine oxide (TOPO)/toluene. The organic extract is then mixed directly with commercial liquid scintillation cocktail without any further purification procedures and the sample counted on a Wallac 1220 Quantulus liquid scintillation counter (LSC). ²⁴¹Pu activity is estimated via the ²⁴²Pu yield monitor acquired by alpha spectrometry measurement. Experimental results for the performance testing of a low-level liquid scintillation spectrometer and the data for the evaluation of the method using standard reference materials are presented.     

An evaluation of trapping compounds used for determining14CO2 by liquid scintillation counting

Four commonly used trapping agents for scintillation counting of¹⁴CO₂ (Hyamine, Primene, ethanolamine and β-phenylethylamine) were assessed under identical conditions, the progress of trapping being measured directly by pressure changes and by liquid scintillation counting. It was found that quantitative absorption required considerably longer periods of time than those previously reported and that absorption at low¹⁴CO₂ pressures was very slow. The effects of pressure and stirring rate were also studied.     

Automation of liquid scintillation data processing

A program was written in the Basic language to handle scintillation counting data by a time-sharing computer. Explanation is given for the use of the program to facilitate the most common types of calculations, as well as the automatic data handling between the spectrometer and the remote computer. The merits of the system are discussed and a sample of the operation and the output is given.     

Simple measurement of14C in the environment using a gel suspension method

A simple analytical method for environmental¹⁴C with a low background liquid scintillation counter was developed. We used a new gelling agent, N-lauroyl-L-glutamic-α,γ-dibutylamide, for the liquid scintillation counting of¹⁴C as CaCO₃ (gel suspension method). Our procedure for sample preparation was much simpler than that of conventional methods and required no special equipment. The samples prepared with the standard sample of CaCO₃ were measured to evaluate the self absorption of the sample, the optimum condition of counting and the detection limit. Our results indicated that the newly developed technique could be efficiently applied for the monitoring of environmental¹⁴C.     

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.     

Simple measurement of actinides in urine using solid-state scintillation

Rapid methods for determination of internal contamination play a key role during emergency situations in particular for incident response teams and affected populations. For this reason, these methods and their particular techniques must be fast, reliable, robust, simple and cost-efficient, as well as providing high-quality throughput. On the other hand, they are characterized by lower precision and they are often biased. The presented method is based on direct measurement of urine using powder scintillator YAP:Ce together with an alkaline medium as a replacement for traditional liquid scintillation cocktail. The overall efficiencies for trivalent actinides (Am-241 and Cm-244) were greater than 85% and 94%.

     

Determination of 210Pb by measurement of 210Pb and its progenies using a liquid scintillation counter

Journal of Radioanalytical and Nuclear Chemistry - Lead-210 is a useful tracer in environmental studies for a wide range of applications, particularly in atmospheric research and geochronology....