Anomalies in quantitative measurement of 40K in natural samples

Journal of Radioanalytical and Nuclear Chemistry - Efficiency calibration by standard materials of known activity is usual protocol for γ-ray spectrometry. In general, 40K activity is measured...     

Accuracy and uncertainty in radioactivity measurement for NAA

The basic assumptions of activation analysis are that the induced radioactivity is proportional to the amount of analyte, and that the quantity of radioactivity can be related simply to the number of counts observed. Quantitative measurement of activity (and of its uncertainty) is not always simple, especially when accuracy better than a few percent is sought. Recent work with ⁷⁷Ge and ⁷⁶As has demonstrated that the accuracy of half-lives in the literature is sometimes insufficient. Despite these and other problems, quantitative understanding and documentation of uncertainties can be accomplished, providing demonstrable quality assurance and supporting claims of traceability to the Système International.     

Application of a low-level anti-coincidence gamma-spectrometer for environmental radioactivity measurement

Sensitive environmental radioactivity measurement using direct γ-spectroscopy needs to be carried out under particular low-level conditions as the quantity to be determined generally is very close to the natural background. Passive shielding of the detectors in addition to electronic suppression of Compton background resulting from scattering of high energy γ-rays in the gemanium detector seems to be the most promising approach to obtain statistically well defined peaks within reasonable measurement time. Results obtained with a heavily shielded anti-coincidence spectrometer installed at the Research Center Jülich, ideally suited for the measurement of low-level environmental radioactivity in various materials are described.     

Liquid scintillation radioassay for low-activity beta-emitter mixtures by the method of least squares

From the practicable viewpoint for environmental radioactivity measurement and monitoring, the liquid scintillation radioassay has been applied to low-level pure-beta and -emitter mixtures by using the most probable value theory. In low activity measurement, it is required to select a suitable emulsion scintillator and to deal with the calculated data statistically. Detection limit for a solution sample has been roughly estimated to be 10^–2 Bq ml^–1.     

Liquid scintillation method for determination of solvent-extracted phosphorus-32 in foods

A method for solvent extraction of radioactive phosphorus as phospho-molybdic acid in foods is described. The use of a carrier can be eliminated due to the quantity of the stable element present in foods. The use of a liquid scintillation technique for counting is discussed, showing the effective elimination of color and chemical quench. The efficiency resulting from the liquid scintillation method of counting makes possible the detection of 10^-5 μc levels of activity in the original sample.     

Liquid scintillation spectrometry of beta-emitters in marine samples

Liquid scintillation spectrometry has become the most widespread method for quantitative analysis of low level -emitters in environmental samples. This technique has been applied in the measurements of ²⁴¹Pu, ³H and ⁹⁰Sr in seawater and sediment samples. ²⁴¹Pu can be measured by direct analysis of an electrodeposited source using - discrimination or by extraction of electrodeposited plutonium into a liquid form compatible with scintillation cocktail. Sediment from Mururoa and Fangataufa atolls showed activities ranging from 18 to 44 Bq/kg. A sediment profile sampled around Bikini Atoll in 1997 showed ²⁴¹Pu activities ranging from 0.3 to 30 Bq/kg. ³H activities in pore water sediment from Mururoa and Fangataufa atolls were of the order of 10³ Bq/m³ which demonstrated its underground origin. ⁹⁰Sr was measured in the presence of ⁹⁰Y. The counting efficiency was 92.41.5% and the background 0.027±0.001 s^-1. The average chemical recovery for ⁹⁰Sr was 673%.     

Liquid scintillation counting of low activity63Ni

A simple and versatile method was developed to detect low specific-activity⁶³Ni with a liquid scintillation counter. High counting efficiency was obtained for a sample containing up to 220 mg of nickel using a mixture of a violet solution of nickel ammine complex and an emulsifier liquid scintillator. The detection limit was 0.06 Bq g^–1 Ni /1.6 pCi g^–1 Ni/ assuming the counting for 1000 min and 95% confidence level.     

The measurement of natural radioactivity in fish and the impact on humans

Natural occurring radioactive materials (NORM) are quite common inthe South African mining and mineral processing industry, concentrations aresuch that uranium is produced as a by-product at certain gold mining sites.Other major industries associated with NORMs are the coal, copper and heavymineral sectors. Legislation in South Africa addresses the allowed yearlyradiation dose to the general public, and adheres to the most common internationallyaccepted standard of 1 mSv/a. The yearly dose is obviously the sum of thecontributions from every individual nuclide from all possible sources. Accordingly,for members of the public, the individual sources are to be evaluated at muchlower levels. This imposes severe constraints on the radioanalytical laboratoryto offer an affordable routine service due to the required sensitivity toanalyse these NORMs and the variety of matrices involved. For fish one isfaced with an LLD requirement of around 1 mBq/kg, which poses problems withdissolution to allow radiochemical separations as direct measurements by -ray spectrometry are not adequately sensitive for all nuclides of interestto assess the yearly dose.     

Performance of HPGe gamma spectrometry system for the measurement of low level radioactivity

Comprehensive quality assurance/quality control procedure is very much necessary to obtain accurate and precise analytical measurement result. This paper discusses the quality control aspects of the High-Purity Germanium (HPGe) based gamma spectrometry system, which has been used for the measurement of low-level radioactivity in environmental samples. The gamma spectrometry system consisting of coaxial n-type HPGe detector having 50% relative efficiency with respect to 7.62 cm x 7.62 cm NaI (Tl), Nuclear Instrumentation Module (NIM) based pulse processing electronic accessories and 8 k MCA. To reduce the background contribution, 7.5 cm thick lead has been placed surrounding the detector. The minimum detectable activities (MDA) with 95% confidence level (for 300 g soil sample and 100,000 s counting time) for important radionuclides such as ²³⁸U, ²²⁶Ra, ²³²Th, ⁴⁰K, and ¹³⁷Cs are 10.4, 4.3, 4.1, 16.9 and 0.1 Bq kg^?1, respectively. The Quality control (X bar R) charts were plotted using ¹³⁷Cs and ⁴⁰K background counts observed periodically, which showed that the fluctuation is well within the confidence limit and confirms the stability of the system. The laboratory has been participating in the proficiency tests (PTs) of the International Atomic Energy Agency (IAEA). In recently concluded PTs, the samples include soil, spiked standard solution, spinach, phosphogypsum and spiked air filter were analysed for the natural, fission and activation products radionuclides. The performance evaluation of the IAEA PTs showed that the laboratory results were in good agreement with the target value, which confirms the reliability and traceability of the gamma spectrometric measurement result of the laboratory.     

Liquid scintillation radioassay for multiple radionuclide mixtures by the most probable value theory

Multiple radionuclide mixtures which have similar scintillation pulse height distributions can be accurately radioassayed by the most probable value theory. This liquid scintillation technique is based on the construction of more observation equations than the number of nuclides to be analyzed. The technique has been applied to³H–¹⁴C–¹²⁵I and³H–¹⁴C–⁵¹Cr mixture samples, and found to be very practicable with the aid of computerized data processing for mixture samples having a wide range (ca. 10 times) of activity ratios.     

Liquid scintillation counting for determination of radionuclides in environmental and nuclear application

Liquid scintillation counting (LSC) is a major technique not only for measurement of pure beta emitting radionuclides, but also radionuclides decay by electron capture and alpha emission. Although it is a conventional radiometric technique, but still a competitive techniques for the measurement of many radionuclides. This paper summaries the major development of this measurement technique in instrumentation, methodology and applications in the past decades. The progresses in the instrumentation and methodology mainly focus on the commercialization of triple-to-double coincidence ratio based LSC techniques and its application in the determination of different radionuclides. An overall review and discussion on the LSC based analytical methods for the determination of major radionuclides in environmental researches, decommissioning of nuclear faculties and nuclear application are presented, in both measurement techniques and sample preparation using radiochemical separation. Meanwhile the problems and challenges in the development and application of the LSC are also discussed.     

Possibility of radioactivity measurement using an isothermal microcalorimeter

Journal of Radioanalytical and Nuclear Chemistry - Generally, short-lived medical isotopes and/or their generators are produced in nuclear reactors and cyclotrons. During the last decade, the...     

The measurement of radioactivity in Italian drinking waters

Drinking waters generally contain variable amounts of radioactivity. Many radionuclides, like ⁴⁰K and those belonging to the natural decay series of ²³⁸U, ²³⁵U and ²³²Th, are transferred to the water from the aquifer rocks by erosion and dissolution mechanisms.In recent years, a great interest arose towards the natural radioactivity in drinking water. The European Council Directive 98/83/EC, subsequently enforced in Italian law, pushed public authorities to organize tap water surveys. Parameter values for radioactivity levels in water are given, according to World Health Organization recommendations. Maximum concentration values for radon are separately proposed in a European Commission Recommendation.For this reason, during the latest years, the Regional Environment Protection Agency (ARPA) has been performing an extensive monitoring of tap waters in the Lombardia district of Italy. Natural radioactivity content was measured to check the compliance with recent European and Italian rules.Analyses were performed by an ultra-low level scintillation counter equipped with an alpha-beta discrimination device. Specifically arranged procedures, requiring quick and easy pre-treatments, allowed to measure gross alpha and beta activity, ²²²Rn, ²²⁶Ra, and uranium isotopes concentrations in a relatively short time. Subsequently, more complex procedures, involving radiochemical separation of radionuclides, are currently being studied for ²¹⁰Pb, ²¹⁰Po and ²²⁸Ra. Method performances were carefully tested by both internal validation procedures and international intercomparison exercises.These procedures have been employed for a wide range screening in the Lombardia district in Italy. Obtained results showed that in most cases gross alpha activity was lower than the parameter value given by the cited regulations. When these values were exceeded, a more detailed survey was planned: at present three of them, in the western and south-western part of Lombardia and in the city of Milan have been carried out.     

Liquid scintillation and Cherenkov counting characteristics of109Cd

When¹⁰⁹Cd is placed in a liquid scintillation counter, 146±1 counts are obtained for every 100¹⁰⁹Cd nuclides which undergo decay. Thus, the average efficiency for each of the two steps in the decay process is 73%. In examining the distribution of energy among the windows available, it was noted that the distribution pattern is quite similar to that of¹⁴C. An average Cherenkov counting efficiency, in water, was found to be 0.0258±0.0005%. Both 0.010M K₂Cr₂O₇ and CHCl₃ quench the count rate, particularly in the lower energy channel, where count rates are suppressed by up to a factor of 20.     

Liquid scintillation counting of radionuclides emitting high-energy beta radiation

Liquid scintillation counting of radionuclides emitting beta radiation with E_max>2 MeV has been investigated. Fluor volume effects were similar to those for low energy beta radiation, and pulse height spectra broadened in a predictable manner with no pulse clipping up to 4.913 MeV. Large changes in sample channels ratio due to color quenching resulted in progressively smaller losses of counting efficiency as beta energy increased. Counting efficiences were estimated to be near 100 percent for³⁴Cl^m,³⁶Cl,³²P and³⁸Cl. Cerenkov counting of³⁸Cl by liquid scintillation counter was volume dependent for both counting efficiency and pulse height spectrum. Counting efficiencies for³⁴Cl^m,³⁶Cl,³²P and³⁸Cl were estimated to be 57.0, 7.5, 42.7 and 66.3%, respectively. Pulse height spectra were shifted to greater pulse heights as a function of beta E_max, supporting the possibility of energy discrimination for beta emitters by Cerenkov pulse height spectrum analysis. The advantage of singles Cerenkov counting over coincidence Cerenkov counting was greatest for³⁶Cl and least for³⁸Cl; this advantage was amplified more for samples of³⁶Cl which had been color quenched than for similarly quenched samples of³⁸Cl or³²P.     

A dipping method for radioactivity measurement in water using plastic scintillator

Journal of Radioanalytical and Nuclear Chemistry - A new dipping method was studied for the measurement of radioactive solution using plastic scintillator sheets and pellets (PSs) and a liquid...     

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%.

     

Liquid scintillation assay of 3H and 14C-labelled polymers

The assay of a range of ³H and ¹⁴C-labelled polymers by liquid scintillation counting is reported. Methods of sample preparation such as combustion, solution, gelation and suspension techniques are described and compared. The validity of a variety of procedures of counting efficiency determination for the above methods is examined and critically discussed.