Accred Qual Assur (2013) 18:105–114 DOI 10.1007/s00769-012-0943-x
PRACTITIONER’S REPORT
Need and use of reference materials in a comprehensive countrywide monitoring of radionuclides Beata Varga • Sandor Tarjan
Received: 2 September 2012 / Accepted: 26 November 2012 / Published online: 13 December 2012 Springer-Verlag Berlin Heidelberg 2012
Abstract The reliability of measurement results is essential for forming a common database of a laboratory network, because a well-maintained and consistent database is the crucial point of countrywide monitoring. Reference materials are important tools in realizing some aspects of quality assurance; they are especially useful in harmonizing work within the network. Among usual types of reference materials in radio analytics solutions, matrix reference materials and some special reference objects are used. All classes of reference materials should be used depending on the purpose of the demonstration of quality, even in-house reference materials. Interlaboratory measurement comparison and performance evaluation programs play important quality assurance role in radio analytical laboratories. Fortunately, nowadays, the main task is to determine a very low radioactivity concentration in the environment; therefore, pre-concentration is necessary. Generally, the radionuclide bearing natural materials collected from sites where there had been sufficient time for natural processes to redistribute various chemically different species of radionuclides are more reliable reference materials than spiked materials—the main difference is the chemical bounding which is crucial from the point of view of the bioavailability. The need of reference material is summarized according to the intended use, like quality control, measurement validation, and instrument calibration. Keywords Reference material Monitoring of radionuclides Quality of the results
Introduction In the field of food and feed monitoring and in environmental monitoring, demonstrating the evidence of the good quality of the analysis is continually requested by customers and governmental organizations. Laboratory working in the frame of the monitoring network has to deal with the legislative limits providing evidence on the quality of its whole operation is highly desirable, moreover demonstrating the quality of the results is mandatory. All factors with a possible effect or influence on the radio analytical result should be carefully documented during all steps of the operation carried out in the frame of an accredited laboratory, like sampling, sample amount reduction, sample preparation, analytical procedures. Usually the quality assurance system and the accreditation help achieve a stable high-level quality of the results. There are lots of tools in the frame of the accreditation system implemented according to ISO EN 17025 which promote the production of reliable results. There is another important reason to keep the good quality of the results in case of the members of a countrywide monitoring network. If all aspects of quality management and all technical aspects are harmonized, the database can be handled as one dataset. A network can work effectively, if tasks are shared according to capabilities. All member laboratories should be accredited according to ISO EN 17025, and the quality assurance should be treated on network level with the following tools:
This paper was presented at BERM-13, June 2012, Vienna, Austria.
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B. Varga (&) S. Tarjan National Food Chain Safety Office, Food and Feed Safety Directorate, Radioanalytical Reference Laboratory, Fogoly Street 13–15, Budapest 1182, Hungary e-mail:
[email protected]
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harmonized methods like common calibration standards, harmonized uncertainty budget, control charts, maintaining procedures; procedures like document handling, reviews, preventive, and corrective actions;
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• •
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same data treatment; central laboratory prepares, organizes, and evaluates intercomparison runs and proficiency tests for the network.
All listed components are necessary for achieving a consistent, well-maintained database which can be treated statistically as only one dataset. By the definition [1], reference material is ‘‘sufficiently homogeneous and stable with reference to specified properties, which has been established to be fit for its intended use in measurement or in examination of nominal properties.’’ Providing the associated uncertainty with reference values is also required. Reference material can be used for measurement precision control whereas only reference materials with assigned quantity values can be used for calibration or measurement trueness control. Reference materials have to be well characterized and homogeneous for a large number of analytes; therefore, they are useful in • • • • •
• •
method validation, method development, long-term performance test of the method (Shewhart and cumulative sum control chart), for defining several property of a method, like repeatability, reproducibility, limit of quantification, assessment and quantification of different sources of uncertainty taking into account uncertainty of the reference material, estimation of accuracy and precision, evaluation of possible interferences,
• • • • • • • •
In the frame of the laboratory’s quality control program, a reference material that is as similar as possible material of routinely measured samples is most useful. For choosing the appropriate reference material, one needs to know well the overall goal of the monitoring program, the goals of the individual measurements, the objective to be achieved with the analysis, the performance of the methods and so on. The concentration range also might be a crucial criterion. For the laboratory, the most valuable materials are those reference materials, which have well-established property values with the associated uncertainty for more analytes, in this case for more radionuclides. According to the wide range of the tasks, the grouping of the need of reference materials is necessary and meaningful. There are three different situations from the point of view of executing the measurements in the frame of the monitoring program: •
Careful attention has to be paid to choosing the appropriate, compositionally similar reference material for the use in the quality program of the laboratory.
Tasks of countrywide monitoring and fit for purpose reference materials
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Many countries establish only one network of radio analytical laboratories for all possible cases that may occur in the country; therefore, the tasks and working fields of a countrywide monitoring network are usually very extensive. The major objectives of the monitoring program are as follows • • • •
to identify radionuclides, to obtain quantitative information in different media, determination of transfer factors between different compartments of the environment, checking the food and feed, comparing the levels with the regulatory limits,
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analyzing the short and long-term tendencies, feasibility studies for different kinds of nuclear installations, studying the geochemical processes, forensics tasks, determination of the (possible) origin of contamination caused by the radionuclides, environmental measurements connecting nuclear industry and the use of nuclear material, determination of the exposure of the population, emergency preparedness.
•
In normal situations, there is sufficient time for the precise nuclide-selective analysis, the concentrations are low, usually several steps of the pre-concentration are needed before the measurements. Results are close to or give the background level. Supporting these work reference materials have to be precisely characterized with sufficiently small uncertainties and should contain low level of radionuclides. For preparing the monitoring network for emergency situation, the regular measurements should be executed with the reference materials containing radionuclides at least 2 orders of magnitude higher than in normal situation. Priority has to be given to measuring regulatory levels precisely. The other difference is that screening methods are more widely used. The time available is much less even for the measurement and the reporting of results—proficiency test with a short reporting time was a very good exercise for the emergency situation (organized by IAEA Seibersdorf Laboratories, Chemistry Unit). Matrices are mainly the same as in case of normal monitoring. The third case is remediation, when usually there is enough time for the analysis, the concentration levels
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vary at a very wide range, usually the isotopes to be identified are known in advance because of the record keeping of the industry or simply coming from the applied industrial processes.
Environmental monitoring Radionuclides can be found in all parts of the biosphere, geosphere, atmosphere, and hydrosphere. Radiological protection of the environment has attracted increasing attention over the last two decades, and there is currently a commonly held view that explicit protection from harmful effects of ionizing radiation should be provided for nonhuman species and ecosystems. There has been a shift in society from the long-held anthropocentric approach to protection of the environment to one that embraces both biotic and, sometimes, abiotic components of the environment. The main goal of the environmental monitoring is giving the evidence about the safe environment. The most informative samples are aerosol filters. Highvolume aerosol filtration systems (higher than 150 m3/h) collect aerosols during 2–7 days, depending on the practice of the laboratory. Glass fiber and HEPA (high-efficiency particulate air) filters are generally applied. After folding or pressing the filters are put into gamma spectrometer systems first (3–4 days cooling time is recommended for waiting of the decay of the short-lived natural radionuclides). If there is a suspicion that the aerosol might contain pure beta or pure alpha emitters, the chemical treatment is unavoidable. On the one hand, the usual environmental levels of radionuclides are desirable, and on the other, the set of the filters should contain above the first group the most common volatile fission and activation products in the order of 1–100 Bq/filter. The expected inhomogeneity between filters is 5 %, within one filter area 3 %. The variety of the size of the high-volume aerosol filters causes problems in preparing the reference material. One solution might be that IRMM [2] had chosen in the frame of an intercomparison, they asked the participating laboratories to provide the blank aerosol filters, and they spiked all of them. Regarding the reference material production, this way is not the optimum solution. The other possible way providing a large homogenous surface is to cut it to the size applicable in laboratory use. This requires a higher degree of the homogeneity of the filter surface than it is achievable by the spiking technique. The inkjet printing technology is widely applied for the scientific research. Using this basic method, a well-known amount of the radioisotopes should be spiked into the ink, and the required surface is printed by the inkjet printer onto the aerosol filter or any carrier
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material depending on the purpose [3]. The activity of the radioactive material can be calculated from the drop size of the printer in advance during the planning process. The direct comparison by point sources is used to the exact activity determination of the printed surface. The monitoring of soil and sediment is always an important part of the monitoring schedule. These media are considered to be the reservoirs of the radioactive isotopes. The chemical forms of the radionuclides determine their movement through the compartments of the environment, and their uptake by biota. There are three main points where the chemical form has a strong influence: • •
•
the chemical form of the radionuclide in the deposition; the way of binding of radionuclides to the soil, this has an influence on the amount of radionuclide in the solution in the soil; chemical form in the solution, which has a significant effect on the ability of organisms to incorporate radionuclides into cells.
Dissolved ions of radionuclides in aquatic system can bind to solids by several processes. The overall process is sorption, which controls the dissolved radionuclides and reduces their mobility in the environment. All positively charged ions in solution compete to fill the sorption sites. Binding to the solid soil surfaces is ion specific. The composition of the sorbed ions at equilibrium depends on the amount of each ion in solution and the selectivity of the sites for each ion. The most usable models are based on empirical solid–liquid distribution coefficients. Based on the above, natural soil found in the course of routine monitoring should be regarded as best reference material. The spiked soil sample will behave in another way than the real one when chemical treatment is necessary for the determination of radionuclides. Complex methods have to be applied, which means parallel or sequential, multiisotopic analysis. The crucial point is the digestion to get correct results. In the case of reference material of natural origin, 1–2 % of inhomogeneity might be achieved. The reference material collected in nature is especially important here, because the natural biogeochemical processes can modify the original state and speciation of the deposition. For the gamma spectrometry, the spiking technique is appropriate. The reference material has always to contain the elements of the natural decay chains. Above this common fission and activation, products and actinoids are the most required isotopes. The recommended inhomogeneity is less than 5 %. For the overall purposes, generally, the 250-g packing unit is necessary. The assigned values are usually given for dry material, so the drying conditions have to be well described on the datasheet of the material.
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The third essential element of the environmental monitoring is water, as it is given even under article 35 and 36 of the Euratom Treaty. Protection of the water reservoirs is very important even from chemical or radionuclide contamination; they might be the target of harmful attacks. Radioactivity might be transferred from water to biota including human beings either directly via drinking water and immersion into the media or indirectly via consumption of another aquatic organism. From an atmospheric source, radioactivity can be deposited onto the catchment of the rivers and the surfaces of any kind of water body. In the catchment, the radioactivity might be washed out into the watercourse rapidly, and in the same time, the deposited radionuclide can adhere to soil or sediment particles which are removed by erosion. Regarding the preparation of the reference material, this is the simplest media. The spiking technique is perfect to make the required composition of radionuclides. There is just one effect which has to be taken into account, namely it is necessary to avoid the sorption of the radionuclides onto the surface of the container. Regarding the derived limit, the situation is much better than for food, because WHO elaborated and published guideline levels for many radionuclides. Radionuclides of interest are most common volatile fission and activation products with the concentration of any kind of regulatory limits. From the analytical point of view, there might be two approaches: On the one hand, to measure the actual radionuclide level of the water, sometimes 50 L of water is needed. For several radionuclides, proving the regulatory limit much less sample, just several tens of milliliters are enough, for example, for tritium. In the case of tritium, it is worth to produce several levels of the samples, several TU for the laboratories dealing with hydrological processes; another one is the current level of the tritium (several Bq/L), and a third one is close to the regulatory limit of drinking water (100 Bq/L). Never acidify samples containing tritium! These samples should cover four orders of magnitude in the concentration range. In case of 14C, the concentration range might be 1–250 Bq/L. The concentration of naturally occurring radionuclides in the reference material should be as high as ten times of the derived concentrations for drinking water (regulation is under preparation in EU). The required inhomogeneity is \3 %, which is rather easy to achieve even in the normal laboratory conditions. One percent might be the requirement for an experienced team. The required amount of the reference material of water strongly depends on the concentration range (is there any need of pre-concentration of the sample?) and the type of the radionuclides to be determined from the same sample—the complex determination methods might cover the determination of several radionuclides at the same time. Generally, 3 L is enough for different radio analytical techniques.
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Nowadays, the need for reference material representing the sludge matrix from water treatment has arisen. The need for determination of primordial radionuclides is increasing. The achievable inhomogeneity is similar to the case of soil, 5 %. 500 g of the sample amount is recommended in dry material. The matrix is aluminum sulfate which concentrates and co-precipitates radionuclides during the treatment process. Bioindicators are readily analyzed in the frame of monitoring. Moss and lichen are integral indicators; the age of them might reach even several decades, so their radionuclide collection period also may be several decades. Determination of the age of the moss would be very useful, and this might identify the collection period. In the aquatic environment, seaweed and shellfish are considered bioindicators.
Monitoring of food and feedstuffs Belonging to the Ministry of Rural Development, our main task is controlling the food and feeding stuffs produced in Hungary. The situation is almost the same as in the case of soil, usually complex nuclide-selective radio analytical methods are applicable. The bulk material of the reference material is usually dried food or feed, which is convenient for handling. Types of food of interest for the society are changing according to the consumption habits, the last big change was the structure of the meat consumption, chicken became most popular. Currently, there are no nuclide-specific limits in force for foodstuffs and feeding stuffs for normal situations and prolonged emergency situation (longer than 1 year). What we have in Europe is just a follow-up regulation of the Chernobyl contamination valid until 2020. This regulation is valid for emergency situation for the initial period of 3 months after the emergency—the revision of the limits is prescribed after the initial period. For analysts and experts dealing with food control, well-defined isotope-specific derived levels would make life much easier. Just to mention an extreme case, if the radio analyst finds high activity concentration of 210Po in the food, there is no possibility of quick withdrawal of the food because of the lack of the derived concentration level; the only possibility is calculating the ingestion dose from the supposed consumption rate and compare the result with the general dose limit for public of 1 mSv/year. This way is an indirect application of the general limit which is not always defendable legally. Baby food should get priority above the basic foodstuffs. Radionuclides of interest taking into account the long-lived and most toxic nuclides are 90Sr, 129I, 137Cs, elements of natural decay series (the most harmful is 210Po), 238Pu,
Accred Qual Assur (2013) 18:105–114 239?240
Pu, 241Am. Keeping record of the 40K content serves identification of the sample type, because the potassium content of the different foodstuffs is a well-defined property; therefore, the 40K content is also characteristic—it might be used for quality control purposes. The required inhomogeneity is \3 %. The desirable amount of the reference material containing several radionuclides among them alpha and beta emitters is 500 g dry or equivalent. During the preparation of reference material, freeze drying is certainly applied. A large amount is necessary because of the use of complex methods. In addition to the checking of fresh and dry feed, feed additives should be controlled as well. The results of the analysis may cause some surprise for the staff of the laboratory. Feed additives are sometimes byproducts of other industrial processes; therefore, for example, the uranium content may be high and not in equilibrium with the other members of its decay chain. The required inhomogeneity is \5 %, and the amount of the material is 500 g dry. Radionuclides of interest are the same as mentioned in the case of foodstuffs.
Marine environmental studies Radionuclides in the marine environment are subject to a plenty of complex biogeochemical reactions. The transport of them is determined by physical processes, by their chemical reactivity, by the biogeochemical properties of the receiving medium. The following processes might determine the migration and form of the radionuclides in the marine environment: dissolution, hydrolysis, complexation with organic and inorganic ions, redox reactions, colloid formation, sorption–desorption at the mineral surfaces, co-precipitation, mineralization. Radionuclide speciation strongly depends on the ionic strength of the sea or ocean water, acidity, redox state, and presence and concentration of complexing inorganic (Cl-, CO32-, SO42-) and organic (fulvate, humate) ligands. Radionuclide might sorb on the suspended particulate material and colloids then might co-precipitate and might be involved in ion-exchange processes. Only tritium is the radionuclide in the marine environment, which enters the solution and remains in dissolved form. For the simplification of the description of the transport 90Sr, 99Tc, 125Sb, 134Cs, 137Cs, 226 Ra, 238U are also supposed to behave in a similar manner. The particle reactive 210Pb, 210Po, 234 Th, 239Pu, 241 Am, 244Cm like to associate to the solid phase, so their transport is determined by the transport of the suspended particulate matter; therefore, it is strongly controlled by the sedimentary processes too. The above-mentioned properties of the radionuclides and processes are essential to be taken into account during
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monitoring and analysis of the samples, moreover during the production of the reference material. Among the matrices required to be analyzed during monitoring, the preparation of the water sample is the easiest one. For tritium, the spiking technique is completely adequate. For 90 Sr, 99Tc, 125Sb, 134Cs, 137Cs, 226Ra, 238U and other isotopes of these elements, spiking is an accepted procedure with careful consideration of modeling well the sea or ocean water regarding salinity, pH, redox state and some more important complexing agents. In case of particle reactive 210Pb, 210Po, 234 Th, 239Pu, 241Am, 244Cm, isotopes’ many other considerations have to be taken into account, and many precautions have to be done, for example, the choice of the container has to be thoroughly considered. For the other media, it is better to find an appropriate amount of the natural material and treat the large amount of the sample according to the requirements of the relevant ISO guides and standards relating to the reference material production and characterization. Anyway, the most important radionuclides are tritium, 90Sr, 129 I, 137Cs, 241Am, elements of the natural decay chain, 237 Np, U isotopes, Pu isotopes. The required inhomogeneity is \5 %, the recommended packing unit is 500 g dry material, and freeze drying is recommended. For water, the best solution is to prepare a large amount of the individual sample as reference material (100 L), but if the shipment causes a big problem, 100 mL of the stock solution might be provided accompanied with careful, detailed instructions how to make the proper dilution for the large amount as usually sampled.
Monitoring during the remediation Many symposia are held dealing with the problem of naturally occurring radionuclides (NORM) and their enhanced level and technologically modified (TENORM) amounts of them. The International Atomic Energy Agency also deals with the topic to wide extent. A thoroughly planned survey has to be conducted in the area which needs to be remediated, then there is a need for the continuous control of the remediation work and after finishing the remediation process the follow-up monitoring has to be carried out. All stages require the analysis of lots of samples; therefore, reference materials are badly needed. It is not an easy task to produce appropriate reference material for this purpose. The spiking technique has to be omitted. The question of radioactive equilibrium and disequilibrium has to be carefully considered. The best solution is to collect a large amount of samples in the field well known about the increased level of natural radioactivity. In case of TENORM, the diversity of the technologies– uranium mining, phosphate industry, zircon
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industry, oil, and gas industry, etc.—also causes some problems; therefore, the collection of the candidate reference material is desirable from a similar site that requires reference material. The usual matrices are soil, scale, water even food and feed. The required inhomogeneity is less than 5–10 % depending on the isotope and the property sought. The required amount is 250 g dry material.
Monitoring during dismantling The nuclear power plants are getting old and getting close to their lifetime. The problem is often prolonged by demanding life extension, but the final decision depends unfortunately not only on the technical conditions of the energy producing blocks of the nuclear power plant. There are several decommissioning strategies, which differ mainly in the cooling time left for the parts—this means also a different handling. Safe enclosure means usually total dismantling after a longer period of time and total dismantling of all systems of the controlled area including buildings after the enclosure time. The other possibility is the immediate dismantling after the necessary planning has been performed and has been licensed, and this means that dismantling starts more or less shortly after the decision of shutting down. The two dismantling strategies require different levels of the radionuclides in the bulk material; the second solution is the more problematic from the point of view of the production and shipment of reference material, because the measured level is high above the exemption level. Besides the lot of measurements in the site, this monitoring work requires a separate area with all the necessary functions in the laboratory. The measurable concentration range is several orders of magnitude higher than in case of environmental monitoring; therefore, it is better to keep even the separate measuring systems for this purpose. The types of required materials range from different types of concrete through the different alloys, sludges, remaining material of evaporators to ionic resins. The required activities are the highest (even 10 MBq/kg) among the reference materials used in the normal and not in emergency situation. Radionuclides of interest are first of all 3H, 14C, 60Co, 137Cs, 16Cl, other gammaemitting activation and fission products. Other big groups are the actinides and lanthanides, beta emitters with long-term dose like 93Zr, 79Se, 107Pd and radio-halogens. In addition to the matrix reference materials, the reference surfaces are also very useful here, especially for the work on the site. The required inhomogeneity is \5 %, and the useful amount for the matrix reference material minimum 1 kg.
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Nonproliferation, forensics States have the responsibilities for combating illicit trafficking and inadvertent movements of radioactive material [4]. The Nuclear Smuggling International Technical Working Group (ITWG) was created in 1996. The members of the ITWG come from a broad range of backgrounds covering law enforcement, safeguards, custom agencies, scientific field including laboratories. Nuclear forensics does not consist of routine procedures that can be universally applied to all evidence. Because the results of a nuclear forensic investigation could be used as evidence in a criminal prosecution, or can affect international estimates of proliferation and threats of terrorism, it is essential that the data and their interpretation be credible. The environmental sample determination encompasses proliferations detection, forensics, and fuel cycle materials that require high-sensitivity or high-accuracy measurements. The identification of the possible origin of the radionuclide contamination has a higher importance than in the usual environmental monitoring, for example, if the isotopic ratio differs from that the global fallout, the source of the contamination has to be determined. The rigorous quality assurance in the laboratory will ensure confidence in the analytical data. Specially designed reference material is needed to ensure quality of the determination of the radionuclide amount for the national security programs [5]. For example, there is a need for the environmental matrices with certified actinide content and isotopic ratios, different ratios of uranium, for example, 235U/238U, 236U/238U, 234 U/238U, isotopic ratio of global fall-out e.g. 241 Pu/239?240Pu, 241Am, amount of different Pu isotopes comparing with 239Pu content. Thermal ionization mass spectrometry and inductively coupled mass spectrometry have become standard methods for determining sub-picogram quantities in environmental samples, so these techniques need reference materials with different isotopic ratios at a very low concentration level. The required inhomogeneity of the isotopic ratios is \3 %. The proper packing unit might be very different according to the requirements of the analytical technique 1–250 g.
Emergency preparedness Following a nuclear accident or a terrorist attack using radiological dispersal device or improvised nuclear device screening of the site and first responders are necessary in very short time. These scenarios might produce serious health, safety, recovery, public relations, and restoration challenges. The identification of the contaminated area and the victims who may have been internally contaminated is essential. The screening results have to be good enough to provide a reliable
Material containing TENORM
Sludge from water (public use) treatment
5%
5%
3%
Enhanced level of NORM and in different elemental 5–10 % and isotopic ratios concentration range might be very wide: 500–50000 Bq/kg
10 times of the natural level
Primordial radionuclides
water: 0.001–5 Bq/L
1–3000 Bq/kg 40 Ocean studies: K, 90Sr, 129I, 137Cs, 241Am elements of natural sediment, shellfish, decay series, 237Np, Pu, 239?240Pu seaweed, fish flesh, sediment: 1–5000 Bq/kg water marine food: 0.1–500 Bq/kg
K, 90Sr, 129I, 137Cs, elements of natural decay series, 238Pu, 239?240Pu, 241Am, 210Po
40
250 g dry
500 g dry
500 g dry
150–500 g dry
500 g dry
3% Biological material— 40K, 90Sr, 129I, 137Cs, elements of natural decay main foodstuffs and series, 238Pu, 239?240Pu, 241Am, 210Po baby food 0.1–500 Bq/kg depending on isotopes and their legal limits
Biological material— fodder, grass, moss
250 g dry
NORM, TENORM most common fission and activation products, actinoides 1–5000 Bq/kg
5%
Soil, sediment
4. NORM in 10 times higher than derived concentrations for drinking water according to WHO recommendation
2. 3H–1–100 Bq/L 3. 14C–1–240 Bq/L
Additional sample preparation: folding or pressing according to the laboratory practice
Remark
Chemically modified forms according to the industrial use
Al(NO3)3—co-precipitates radionuclides during the treatment process
Freeze drying technique for the preparation
The drying conditions have to be given
pork muscle 130 C
milk powder 110 C
rye, wheat 130 C
Recommended temperature of preparation of RM for example
The drying conditions has to be given
3. for 3H measurement it is forbidden to acidify the sample
3 L allows to use the same RM 1. gamma-sp without sample prep, just filling the for different radioanalytical usual geometry and seal thoroughly techniques 2. with or without distillation, depending on the solution beta-emitting nuclides
1. most common volatile fission and activation products, concentration around the limits
Water 3 % is desirable between lots
1. usual environmental level Between the filters: 5 % Area fitted to the general use, e.g. 0.4 9 0.7 m 2. usual environmental level and most common within one volatile fission and activation products in the order of filter area: 3 % 1–100 Bq/filter depending on the isotopes
Packing unit of RM
Aerosol filter (glass fiber, HEPA)
Inhomogeneity
Radionuclides, concentration range
Purpose and matrix
Table 1 Summary of important features of reference materials needed in countrywide monitoring
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Pu,
244
Np for alpha
236
Cl
16
Concentration should be around the exemption level, and some material has to reach even the dangerous values of radioactive isotopes
5. beta emitters with long-term dose: 93Zr, 79Se, 107Pd and radiohalogenes
4. actinoides, lantanoides
3. other gamma emitters
Cs,
137
Co,
C
2.
60
14
1. 3H,
Total amount of reference materials are usually low
5.
4. support for forensic investigations - isotopic ratios of actinoides, 240Pu/239Pu for ICP-MS, age of nuclear material (parent–daughter)
3. isotopic ratio of global fall-out (e.g. 241Pu/239?240Pu, 241Pu/241Am)
5%
2. recommended acceptance criteria of measurement
1. taking into account uncertainty of the measurement in compliance assessment
There is a need to establish a rule
Consider the terrorist attack using radiological dispersal device or improvised nuclear device; the activities during the discovering, early response, recovery, restoration
Cannot be treated in the same laboratory as the other environmental material
RM reference material, HEPA high-efficiency particulate air, NORM naturally occurring radioactive material, WHO world health organization, TENORM technologically enhanced naturally occurring radioactive material
7. concrete, asphalt
6. food and vegetation
5. swipes
4. large–volume, low-density material: water or gel
1 kg
1 kg
1–25 g
Might be very different amounts Identification of origin of the radionuclide (global according to the requirement fall-out or source has to be determined) the analytical technique:
Ratio 3 %
Remark
Packing unit of RM
Inhomogeneity
5% Emergency following Neutron screening; 3 an accident or H, 60Co, 88Y, 89Sr, 90Sr, 129I (131I), 134Cs/137Cs, 147 terrorist attack: Pm, 192Ir, 210Po, 226Ra, 244Cm, 252Cf, 1. hair, dry urine and Pu, Th, U in different ratios ashed fecal sample Concentration required 10–1000 times of the normal 2. aerosol filter use of reference material 3. large surfaces for checking the surface contamination,
2. sludge or concentrates from evaporators, ionic resins
Materials connected with dismantling 1. concrete
1. Depleted uranium
RMs with certified isotopic ratios
2. different ratios of uranium, for example, 235U/238U, 236 238 U/ U, 234U/238U
Radionuclides, concentration range
Purpose and matrix
Table 1 continued
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input for the consequence management and decision making. The reliable radio analytical results are essential for the decision-making process beginning in the early response through the recovery and restoration phases of the event. There is a need for some special reference material in addition to the usual matrix type. First of all reference material has to be available for gross-alpha and gross-beta measurements, for neutron screening and a reference surface for the determination of surface contamination. The sample types cover all usual materials: hair, dry urine, ashed fecal sample, aerosol filter, large-volume, low-density material, swipes, food, feed, other vegetation, concrete, asphalt, etc. The most important radionuclides are 3H, 60 Co, 88Y, 89Sr, 90Sr, 129I (131I), 134Cs, 137Cs, 147Pm, 192Ir, 210 Po, 226Ra, 244Cm, 252Cf, and Pu-, Th- and U isotopes in different ratios. The concentration range has to be higher than the normal environmental level. The levels may be determined by the multiplication of the regulatory limits for the different isotopes, the recommended multiplication factors are 1, 2, 10, and 0.5, 0.1. The required inhomogeneity has to be kept under 5 %, but the acceptance criteria of the intercomparison and proficiency test in case of the screening measurements have to be rather high, namely 20–50 % depending on the technique. The required amount of the sample might vary between 10–1000 g depending on the matrix.
Summary In the frame of the laboratory quality assurance program, one of the most valuable tools for obtaining reliable results is the use of reference materials. Intercomparisons are needed to establish comparability of the radio analytical measurements in the network. Proficiency tests are necessary to demonstrate the adequacy of the applied analytical technique. The readiness exercises are needed to demonstrate measurement capabilities under simulated conditions of an event for the sake of the emergency preparedness. Homogeneity of reference material is one of the crucial criteria of production of reference material. For a reference material, it must be ensured that the stated values in datasheet are valid for all packing units. In addition, the stated values must be valid for all subsamples from a packing unit. Accordingly, a distinction is made between homogeneity between packing units and homogeneity within packing units. The purpose of homogeneity assessment is to quantify the level of residual inhomogeneity after all steps of production of reference material. In addition, associated contributions to the uncertainty budget of the stated value have to be evaluated. The procedure for homogeneity testing and evaluation of associated uncertainty contributions complies with the recommendations of
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ISO Guide 35. The Guide is focused on batch certification, for example, the prepared material is split among several packing units. The reference material producers like to use the inverse term, the inhomogeneity, because it is more expressive. There are several factors which have to be taken into account when inhomogeneity requirements are determined: • • • • • • •
statistical behavior of radioactive decay, properties of decay of radionuclide, decay data of radionuclides, properties of applied measurement techniques, counting statistics, repeatability and reproducibility of the method applied, intended use of reference material.
The commutability of the reference materials gets more and more emphasis, because of economical reasons and because of the questionable availability of reference materials that were used for several ages and are hardly available now. Commutability is defined as the equivalence of the mathematical relationships between the results of different measurement procedures for a reference material and for representative samples. This material characteristic is of special importance for measurement procedures that are optimized for measuring analytes directly. The commutability of a reference material is measurement procedure specific, and its assessment requires special experimental designs. The commutability is the property of a reference material, demonstrated by the closeness of agreement between the relation among the measurement results for a stated quantity in this material, obtained according to two given measurement procedures, and the relation obtained among the measurement results for other specified materials. Reference materials can be commutable for some measurement procedures but may be noncommutable for others. The applicability of a reference material for general use as a trueness control depends on the number of measurement procedures for which it was found commutable. The existing approaches use descriptive statistics or some form of regression analysis to compare the numeric relationships among results of different reference materials. All assessment procedures for commutability are based on determining the mathematical relationship and distribution of results observed for one reference material, and determining whether the results of another reference material are members of the same distribution. Linear or polynomial regression with two-tailed 95 % prediction interval to assess the commutability of materials is used generally. There is another approach based on evaluation of the normalized residuals from regression analysis, and an acceptance criterion has to be determined usually in term of 2 or 3 times of standard deviation of results of one of the reference material. The
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approaches using multivariate descriptive statistics utilize principal component or correspondence analysis to compare relationships’ results of one reference materials to those for another reference material. This approach has the advantage that it allows comparison of multiple materials with multiple methods in one graph. The stability of the commutable reference materials should be monitored regularly. The demonstration of commutability is very useful when some in-house reference materials are produced and used for quality assurance purposes. There is a need for consensus guidelines to enable consistent assessment of commutability of reference materials. Having consistent procedures is of special importance considering the increasing number of reference materials that have been introduced with the intended use to establish or to verify trueness for routine measurement procedures. Table 1 summarizes the important features of reference materials needed in a comprehensive monitoring of radionuclides.
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and 35, and guides on the preparation of working level reference materials are also available. All or some of the requirements may be specified in the customer and radio analytical specification, but often it will be necessary for the radio analyst to use professional judgment. Finally, quality does not necessarily equate to small uncertainty and fitness for purpose criteria need to be used. Regarding to reference materials containing radionuclides easiest to get soil and sediment samples, other matrices are not so easy to get. Aerosol filters are urgently needed, not only as part of an inter comparisons or proficiency tests. There is a special problem with radioisotopes having short half-life—usually usable period of these reference materials is short, even they are hardly available; some of them are frequently occurring in case of emergency situation. There is lot of things to do in the field of production of reference materials containing radioisotopes.
References Conclusion Generally, the demand for reference materials exceeds supply in terms of the range of materials and availability. It is important that users and accreditation bodies understand any limitations of reference materials employed. There are, however, several hundred organizations producing tens of thousands of reference materials worldwide. The distinction between government institutes and commercial businesses is disappearing with the privatization of a number of national laboratories. Guidance on the preparation of reference materials is given in ISO Guides 31, 34,
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1. International Vocabulary of Metrology Basic and general concepts and associated terms, 3rd edn, Joint Committee for Guides in Metrology (JGCM 200:2012) 2. Watjen U et al. (2007) Evaluation of EC measurement comparison on simulated airborne particulates—137Cs in air filters, Report EUR 22926 EN, 2007, ISBN 978-92-79-06962-8 3. Tarjan S, Varga B (2012) New techniques for preparing reference materials, 13th international symposium on biological and environmental reference materials (BERM 13) 25–29, Vienna 4. Nuclear Forensics Support (2006) Reference Manual, International Atomic Energy Authority, Vienna 5. Inn KGW et al (2008) A blueprint for radioanalytical metrology CRMs, intercomparisons, and PE. Appl Radiat Isot 66:835–840
