NUCLEAR PROFICIENCY TESTING: The 1st International Workshop on Proficiency Testing in Applications of the Ionizing Radiation and Nuclear Analytical Techniques in Industry, Medicine, and Environment
1036(2008); http://dx.doi.org/10.1063/1.2979087View Description Hide Description
Confidence that a testing or calibration laboratory consistently obtains reliable results is of major importance to users of laboratory services and participation in proficiency testing schemes provides laboratories with an objective means of assessing and demonstrating the level of confidence that can be ascribed to the reliability of the data they are producing. That level of confidence, in turn, depends on the quality of the proficiency tests and, in particular, on the accuracy of the property values associated with the test samples. In the ideal situation, the relevant property value, such as the activity of a particular radionuclide in a test matrix, will be directly traceable to the SI via comparisons with a national or international metrology institute (NMI). This, in turn, begs the question of, how reliable are the results from that NMI.
Demonstration of that reliability at the highest metrological levels is achieved through inter‐laboratory comparisons that are conducted between national and international metrological institutes. These are coordinated primarily by the Bureau International des Poids et Mesures (BIPM) via Key Comparisons or by comparisons within Regional Metrological Organisations (RMOs), with the results from those RMO exercises being linked to the BIPM Key Comparison results. Such programmes have been in place for many years but they have grown in importance and frequency over the past decade. Tabulation of these comparison data has been regularized recently and made available to the user communities via the BIPM Key Comparison Database (KCDB).
In the field of ionizing radiation, the radionuclide metrology discipline exhibits a number of special features. For example, these include the number of potential radionuclides in a user sample; the variety of physical and chemical formats that may be presented; the statistical and temporal effects of radioactive decay; the variations in primary standardization techniques; and the restricted applicability of those primary standardization techniques to the full range of potential radionuclides and activities. Each of these, singly or in combination, ensure that there can never be a fully comprehensive set of Key Comparisons which will cover the requirements of the user community and, in turn, compromise the ability to provide a full range of proficiency tests for testing and calibration laboratories.
These problems are discussed, in the context of radioactivity measurements, together with the structure and range of Key Comparisons and associated databases at the highest international level that are currently in place to underpin the proficiency tests that are necessary for the user communities in this field of application.
1036(2008); http://dx.doi.org/10.1063/1.2979073View Description Hide Description
The paper presents the most significant actions which a primary Radionuclide Metrology Laboratory must accomplish, in order to disseminate the international equivalence to the entire national traceability chain: absolute standardization methods and demonstration of international equivalence, construction and calibration of a consistent set of secondary standardization equipment, preparation of radioactive standards. Delivery of radioactive standards to the end users and carrying out metrological services. Organization of national proficiency tests with the users. International validation of secondary standards by proficiency tests and establishment of a Quality System Assurance.
1036(2008); http://dx.doi.org/10.1063/1.2979083View Description Hide Description
Participation in interlaboratory comparisons provides laboratories an opportunity for independent assessment of their analytical performance, both in absolute way and in comparison with those by other techniques. However, such comparisons are hindered by differences in the way laboratories participate, e.g. at best measurement capability or under routine conditions. Neutron activation analysis laboratories, determining total mass fractions, often see themselves classified as ‘outliers’ since the majority of other participants employ techniques with incomplete digestion methods. These considerations are discussed in relation to the way results from interlaboratory comparisons are evaluated by accreditation bodies following the requirements of Clause 5.9.1 of the ISO/IEC 17025:2005. The discussion and conclusions come largely forth from experiences in the author’s own laboratory.
1036(2008); http://dx.doi.org/10.1063/1.2979084View Description Hide Description
The most recent definition of measurement result requires a statement of uncertainty whenever results obtained by nuclear or other quantitative methods of analysis are reported. Proficiency testing (PT) therefore must include the ability of laboratories to present not only unbiased quantity values, but reliable estimates of their uncertainty. Hence, a reference value with the smallest possible uncertainty is needed to ascertain the proficiency of laboratories reporting results with lower than average uncertainty. A strategy based on the T‐statistic is proposed leading to an accepted reference value that fully reflects the uncertainties reported by participants in a PT‐scheme and permits calculation of En numbers to distinguish whether or not measurement results are consistent with the accepted definition of the measurand. The strategy is applied to PT‐data from a recent international laboratory intercomparison of uranium isotopic ratios with very low reported uncertainties. In the paper this example is used to present the situation in the nuclear field.
1036(2008); http://dx.doi.org/10.1063/1.2979085View Description Hide Description
In the accreditation process of a radioactivity measurements laboratory, according to ISO standard 17025, proficiency tests play a fundamental role. These PTs constitute an irreplaceable tool for the validation of measuring methods. In the case of Spain, ENAC, which is the Spanish accreditation national body, requires that the laboratory has to take part in a PT for each one of the accredited measuring methods in the period of time between two reassessments of the accreditation, what happens every 4–5 years. In specific areas of determination procedures, among which radioactive measurements could be included, the number of methods which can be accredited is very large. The purpose of the present work is to establish a classification into families of the different radioactivity measurement procedures, as well as to establish complementary actions that guarantee that carrying out periodically proficiency‐tests on any of the included procedures in each family, every measurement procedure include in that family is controlled, complying with the criteria established by ENAC.
Assuring the Quality of Test Results in the Field of Nuclear Techniques and Ionizing Radiation. The Practical Implementation of Section 5.9 of the EN ISO/IEC 17025 Standard1036(2008); http://dx.doi.org/10.1063/1.2979086View Description Hide Description
The paper aims to present a practical approach for testing laboratories to ensure the quality of their test results. It is based on the experience gained in assessing a large number of testing laboratories, discussing with management and staff, reviewing results obtained in national and international PTs and ILCs and exchanging information in the EA laboratory committee.
According to EN ISO/IEC 17025, an accredited laboratory has to implement a programme to ensure the quality of its test results for each measurand. Pre‐analytical, analytical and post‐analytical measures shall be applied in a systematic manner. They shall include both quality control and quality assurance measures.
When designing the quality assurance programme a laboratory should consider pre‐analytical activities (like personnel training, selection and validation of test methods, qualifying equipment), analytical activities ranging from sampling, sample preparation, instrumental analysis and post‐analytical activities (like decoding, calculation, use of statistical tests or packages, management of results).
Designed on different levels (analyst, quality manager and technical manager), including a variety of measures, the programme shall ensure the validity and accuracy of test results, the adequacy of the management system, prove the laboratory's competence in performing tests under accreditation and last but not least show the comparability of test results.
Laboratory management should establish performance targets and review periodically QC/QA results against them, implementing appropriate measures in case of non‐compliance.
Implementation of IAEA /1/INT/054 Project in Nuclear Analytical Techniques Group of Argentina: Current State1036(2008); http://dx.doi.org/10.1063/1.2979088View Description Hide Description
This paper presents the implementation of the training received through the IAEA Project “Preparation of Reference Materials and Organization of Proficiency Tests Rounds” in the Nuclear Analytical (NAT) Group of CNEA. Special emphasis is done on those activities related to the first Proficiency Test being carried out by the NAT Group.
A Possible Tool for Checking Errors in the INAA Results, Based on Neutron Data and Method Validation1036(2008); http://dx.doi.org/10.1063/1.2979089View Description Hide Description
This work presents preliminary results of a new type of possible application in the INAA experiments of elemental analysis, useful to check errors occurred during investigation of unknown samples; it relies on the INAA method validation experiments and accuracy of the neutron data from the literature. The paper comprises 2 sections, the first one presents—in short—the steps of the experimental tests carried out for INAA method validation and for establishing the ‘ACTIVA‐N’ laboratory performance, which is‐at the same time‐an illustration of the laboratory evolution on the way to get performance. Section 2 presents our recent INAA results on CRMs, of which interpretation opens discussions about the usefulness of using a tool for checking possible errors, different from the usual statistical procedures. The questionable aspects and the requirements to develop a practical checking tool are discussed.
1036(2008); http://dx.doi.org/10.1063/1.2979090View Description Hide Description
The scheme of European measurement comparisons to verify radioactivity monitoring in the European Union is briefly explained. After a review of comparisons conducted during the years 1990, the approach of IRMM organising these comparisons since 2003 is presented. IRMM is providing comparison samples with a reference value traceable to the SI units and which is fully documented to all participants and national authorities after completion of the comparison. The sample preparation and determination of traceable reference values at IRMM, the sample treatment and measurement in the participating laboratories, as well as the evaluation of comparison results are described in some detail using the example of an air filter comparison. The results of a comparison to determine metabolised and in milk powder are presented as well. The necessary improvements in the estimation of measurement uncertainty by the participating laboratories are discussed. The performance of individual laboratories which have participated in at least four comparison exercises over the years is studied in terms of observable trends.
1036(2008); http://dx.doi.org/10.1063/1.2979069View Description Hide Description
For 40 years, STEME (Environmental Sample Processing and Metrology Department) organized international proficiency testing (PT) exercises formerly for WHO (World Health Organization) and EC (European Community) and currently for ASN (French Nuclear Safety Authority). Five PT exercises are organized each year for the measurement of radionuclides (alpha, beta and gamma) in different matrixes (water, soil, biological and air samples) at environmental levels. ASN can deliver a French ministerial agreement to participate on environmental radioactivity measurements French network for laboratories asking it . Since 2006, November, STEME is the first French entity obtaining a COFRAC (French Committee of Accreditation) accreditation as “Interlaboratory Comparisons” for the organization of proficiency tests for environmental radioactivity measurement according to standard International Standard Organization (ISO) 17025 and guide ISO 43–1. STEME has in charge to find, as far as possible, real sample or to create, by radionuclide adding, an adapted sample. STEME realizes the sampling, the samples preparation and the dispatching. STEME is also accredited according to Standard 17025 for radioactivity measurements in environmental samples and determines homogeneity, stability and reference values. After the reception of participating laboratories results, STEME executes statistical treatments in order to verify the normal distribution, to eliminate outliers and to evaluate laboratories performance.
Laboratories participate with several objectives, to obtain French agreement, to prove the quality of their analytical performance in regards to standard 17025 or to validate new methods or latest developments. For 2 years, in addition to usual PT exercises, new PT about alpha or beta measurement in air filters, radioactive iodine in carbon cartridges or measurement of environmental dosimeters are organized. These PT exercises help laboratories to improve radioactive measurements and to rectify old mistakes. The PT exercises organized by STEME are becoming essential for French and some European laboratories working in radioactive measurements.
The STEME organization, in respect of accreditation references, is presented.
Proficiency Testing as a tool to monitor consistency of measurements in the IAEA/WHO Network of Secondary Standards Dosimetry Laboratories1036(2008); http://dx.doi.org/10.1063/1.2979070View Description Hide Description
The International Atomic Energy Agency (IAEA) and the World Health Organization (WHO) established a Network of Secondary Standards Dosimetry Laboratories (IAEA/WHO SSDL Network) in 1976. Through SSDLs designated by Member States, the Network provides a direct link of national dosimetry standards to the international measurement system of standards traceable to the Bureau International des Poids et Mesures (BIPM). Within this structure and through the proper calibration of field instruments, the SSDLs disseminate S.I. quantities and units.
To ensure that the services provided by SSDL members to end‐users follow internationally accepted standards, the IAEA has set up two different comparison programmes. One programme relies on the IAEA/WHO postal TLD service and the other uses comparisons of calibrated ionization chambers to help the SSDLs verify the integrity of their national standards and the procedures used for the transfer of the standards to the end‐users. The IAEA comparisons include air kerma and absorbed dose to water coefficients. The results of the comparisons are confidential and are communicated only to the participants. This is to encourage participation of the laboratories and their full cooperation in the reconciliation of any discrepancy.
This work describes the results of the IAEA programme comparing calibration coefficients for radiotherapy dosimetry, using ionization chambers. In this programme, ionization chambers that belong to the SSDLs are calibrated sequentially at the SSDL, at the IAEA, and again at the SSDL. As part of its own quality assurance programme, the IAEA has participated in several regional comparisons organized by Regional Metrology Organizations.
The results of the IAEA comparison programme show that the majority of SSDLs are capable of providing calibrations that fall inside the acceptance level of 1.5% compared to the IAEA.
1036(2008); http://dx.doi.org/10.1063/1.2979071View Description Hide Description
As part of its international water proficiency testing (PT) scheme, ‘Aquacheck’, the LGC Proficiency Testing Group has established a new water radiochemistry PT scheme. The PT scheme is aimed at laboratories who undertake radiochemical analysis on drinking water samples as part of an environmental monitoring programme. Following a scheme design and feasibility study, the new scheme was established to monitor the laboratory performance of participants undertaking the determination of gross alpha, gross beta and tritium activity. Three rounds of the new water radiochemistry PT scheme are now complete. This paper explains the process of establishing such a scheme, reviews the results so far, and addresses future development of the scheme.
1036(2008); http://dx.doi.org/10.1063/1.2979072View Description Hide Description
Mushroom reference materials have been prepared and characterized for the use in proficiency tests according to a procedure established within the frame of an IAEA Interregional Technical Cooperation Project. The materials were used for conducting the proficiency tests in Poland in 2005–2007. The results obtained by participating laboratories are presented and discussed.
Monte Carlo Solutions for Selected Problems in Gamma‐Ray Spectrometry and Nuclear Activation Analysis1036(2008); http://dx.doi.org/10.1063/1.2979074View Description Hide Description
A comprehensive calibration of gamma‐ray spectrometers cannot be obtained purely on experimental basis. Problems like self‐attenuation effects, coincidence‐summing effects and non‐uniform source distribution (resulting e.g. from neutron self‐shielding in NAA) can be efficiently solved by Monte Carlo simulation. The application of the GESPECOR code to these problems is presented and the associated uncertainty is discussed.
1036(2008); http://dx.doi.org/10.1063/1.2979075View Description Hide Description
Nuclear Training Centre (CPSDN) is developing, since 1970, the post secondary school and post university training of the personnel involved in the nuclear field and/or in the related areas. Organized, since 1996, as a Department within the National Institute for Physics and Nuclear Engineering, CPSDN is contributing both to the professional specialization of personnel involved in nuclear research, and to the dissemination of the research results. CPSDN training programmes were permanently adjusted to the objective suggested by the beneficiaries/participants, taking into account their background and training necessities. With almost 50 years of training experience in the nuclear field, CPSDN is prepared to face the new challenges related to the compliance with European practices and increased concern on the safe development of nuclear applications.
1036(2008); http://dx.doi.org/10.1063/1.2979076View Description Hide Description
As part of an interlaboratory comparison in order to certify a synthetic material to be used for the validation of the proper implementation of k0‐NAA a collaborative trial was organised. Based on this collaborative study values (repeatability relative standard deviation) ranging typically from 1 to 2% could be achieved, while values (reproducibility relative standard deviation) ranged typically from 2 to 5%. These values were then compared with the Horwitz criterium leading to HORRAT values in most cases well below 1, although two exceeding 1, depending on the element to be determined. It could be concluded that ‐NAA is a very precise method, but that still some inconsistencies for certain elements do exist.
A Small Radioactive Source in a Large Media—Localization by Multi‐detector Measurement. The Case of a Lung Counter1036(2008); http://dx.doi.org/10.1063/1.2979077View Description Hide Description
Considerable errors in the determination of radioactive contamination in lungs can be induced if there is no homogeneous distribution, as assumed for the calibration. Modern lung counter systems use several detectors, and the count rate ratios of the detectors can be used for localization of the radioactive contamination, enabling the use of correction algorithms. This greatly reduces the errors in the determination of the activity. Further reduction of the errors can be obtained by simultaneous analysis of several gamma lines (if several energies are emitted by the radioisotope), and by optimizing the number and location of the detectors. This presentation deals with the case of a point source of natural uranium in human lungs.
1036(2008); http://dx.doi.org/10.1063/1.2979078View Description Hide Description
Whenever there is a risk of occupational exposure to dispersible radioactive material, it is necessary to have a monitoring program to assess the effective dose arising from the intake of radionuclides by workers. In this paper we present our experience in bioassay measurements of in urine samples of workers using high resolution gamma spectrometry. For a 24‐hour excretion period, we found activity values of the order of one Bq and estimated the committed effective doses to be less than one μSv. Although very small, these values led to a re‐evaluation and improvement of the laboratory safety conditions. We discuss the calibration procedure followed for the activity measurements, the estimation of the uncertainty in the excreted activity, the calculation of detection and quantification limits and estimation of performance indicators. Aspects regarding the spectral analysis, true coincidence summing and matrix effects are also considered.
1036(2008); http://dx.doi.org/10.1063/1.2979079View Description Hide Description
PGNAA is a very widely applicable technique for determining the presence and amount of many elements simultaneously in samples ranging in size from micrograms to many grams. PGNAA is characterized by its capability for nondestructive multi‐elemental analysis and its ability to analyse elements that cannot be determined by INAA. By means of this PGNAA method we are able to increase the performace of INAA method. A facility has been developed at Institute for Nuclear Research—Piteşti so that the unique features of prompt gamma‐ray neutron activation analysis can be used to measure trace and major elements in samples. The facility is linked at the radial neutron beam tube at ACPR‐TRIGA reactor. During the PGNAA—facility is in use the ACPR reactor will be operated in steady‐state mode at 250 KW maximum power. The facility consists of a radial beam‐port, external sample position with shielding, and induced prompt gamma‐ray counting system.
Thermal neutron flux with energy lower than cadmium cut‐off at the sample position was measured using thin gold foil is: with a cadmium ratio of:80.
The gamma‐ray detection system consist of an HpGe detector of 16% efficiency (detector model GC1518) with 1.85 keV resolution capability. The HpGe is mounted with its axis at 90° with respect to the incident neutron beam at distance about 200mm from the sample position. To establish the performance capabilities of the facility, irradiation of pure element or sample compound standards were performed to identify the gama‐ray energies from each element and their count rates.