# European metrology network for radiation protection:
Quality infrastructure for a stronger Europe

Annette Röttger, Britt Wens, Amra Sabeta, Robert Bernat, Vladimír Scochor, Teemu Siiskonen, Christelle Adam-Guillermin, Attila Veres, Massimo Pinto, Michal Derlacinski, et al.

► To cite this version:

Annette Röttger, Britt Wens, Amra Sabeta, Robert Bernat, Vladimír Scochor, et al. European metrology network for radiation protection: Quality infrastructure for a stronger Europe. IMEKO 2024 XXIV World Congress, IMEKO - International Measurement Confederation; PTB - Physikalisch-Technische Bundesanstalt, Aug 2024, Hambourg (Germany), Germany. pp.101826, 10.1016/j.measen.2025.101826. hal-05079393

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# European metrology network for radiation protection: Quality infrastructure for a stronger Europe

## ARTICLE INFO

Keywords:

EURAMET

Strategic research agenda

Network

Radiation protection

Quality infrastructure

Euratom

## ABSTRACT

To better protect European citizens, the EU's radiation protection regulations have become increasingly more sophisticated.

Innovative technological developments and new threats can lead to new radiation exposure scenarios. Measures to respond to these new needs come by regulation and include for example increasingly restrictive exposure limits, the introduction of new reference values, and enhanced quality assurance requirements for legal dose assessment. Can metrology support the increasing needs laid down by regulation and ensure by this that Europe has a world-leading metrology capability, based on high-quality scientific research and an effective and inclusive infrastructure, that meets the rapidly advancing needs of end users? To do this, EURAMET has set up European Metrology Networks (EMN). Currently there are twelve EMNs: Advanced Manufacturing, Clean Energy, Climate and Ocean Observation, Energy Gases, Laboratory Medicine, Mathematics and Statistics, Pollution Monitoring, Quantum Technologies, Radiation Protection, Safe and Sustainable Food, Smart Electricity Grids and Smart Specialisation in Northern Europe.

The European Metrology Network for Radiation Protection (EMN RP) responds to the technical developments and aims to act as a single point of contact to cover the metrological needs related to radiation protection. To enable quality assurance in all areas, the network fosters a harmonised, sustainable, coordinated and smartly specialised infrastructure to underpin the needs expressed by stakeholders and in the European regulations for radiation protection. This includes the close cooperation with organisations that are key in the international work for radiation protection like IAEA and ICRP or key for metrology like BIPM with CCRI and EURAMET with TC-IR. A special focus of the EMN is a cooperation with regulators and standardization bodies to actively contribute to the generation of new and to the revision of existing standards (ISO, IEC and CEN/CENELEC).

The aim of the network is to support quality management in all radiation protection issues, to support the development of more harmonised service procedures and capabilities, analyse the needs and give support to research, and by this to contribute to the improvement of radiation protection as a whole. By doing so, the EMN for Radiation Protection improves the understanding of general metrology aims: quality assurance, quality of data and low uncertainties in measurements.

The EMN for Radiation Protection presents within this contribution a research agenda designed to ensure that suitable reference fields and standards can be developed to support radiation protection regulations, to address knowledge transfer requirements and to provide input to international standards. Based on the possibilities offered by European funding programmes (Euratom and Horizon Europe), the EMN members propose joint research projects with the intention to develop solutions suitable for practical applications, develop new calibration services and facilitate the launch of new technologies.

## 1. Introduction

Radiation protection is a scientific success story. After the initial euphoria about the fascinating possibilities of imaging using X-rays, perceptions quickly began to change. Just one year after the discovery of X-rays, the term "radiation protection" was first coined and defined by the American engineer Wolfram Fuchs [1]. He formulated the following recommendations: 1. to keep the exposure as short as possible; 2. not to come closer than 30 cm to the X-ray tube; and 3. to coat the skin with Vaseline and leave an additional layer on the most exposed area. This gave rise to a new skill: radiation protection.

Today, this achievement by Fuchs would be described as a technology-accompanying extension of expertise and we all would be enthusiastic about the brevity of this innovation cycle. Unfortunately, it was not immediately possible to establish this milestone in the handling of ionising radiation. As a result, early radiologists went down in scientific history as "martyrs" with cases of severe radiation burns, subsequent amputations and deaths from cancer [2]. The discovery of radioactivity was initially celebrated enthusiastically and then demonised due to the consequences of improper handling, military use and technical failure. This created growing pressure to develop appropriate methods for radiation protection and emergency response, which was

<footnote>This article is part of a special issue entitled: Supp: IMEKO 2024 published in Measurement: Sensors.</footnote>
successful: radiation protection overcame scientific challenges and achieved greater social acceptance for the topic. It is to this credit that today it is once again easier to see ionising radiation for what it is: a natural phenomenon that can be used responsibly for the benefit of people and society. This responsibility is formulated not least in the radiation protection legislation [3,4] in Europe.

## 1.1. Challenges coming by regulation

In order to better protect people in Europe against the harmful effects of ionising radiation, the requirements for radiation protection have become increasingly complex and challenging in recent decades within the framework of European directives. Radiation protection experts are increasingly reaching their limits when trying to utilise measurement technology for their complex measurements that is actually suitable for the measurement purpose. Whereby suitability in the legal metrological sense (for verification or type testing of ambient, personal and diagnostic dosemeters for photon radiation) means that requirements are met by the measuring devices in order to comply with the state of the art to ensure correct measurement results. In addition, calibration describes a measurement process for determining and documenting the deviation of a measuring device and thus provides a traceability to the SI system of units [5]. Both verification and calibration require that the parameters of the reference fields or standards used correspond to the application: In other words, if the conformity assessment of a dosemeter has been carried out for a specific energy range, this does not prove its suitability for lower or higher energies. The same applies to pulsed radiation: If the suitability of a dosemeter for measurements in pulsed radiation fields is not tested as part of the type test, it cannot be assured that the dosemeter will display correct measured values in pulsed radiation fields. It is also important to bear this process in mind when calibrating radiation measurement technology: For example, a measuring device calibrated for the activity concentration of Rn-222 can provide incorrect values in mixed atmospheres of Rn-222 and Rn-220, even if it has been calibrated in accordance with ISO/IEC 17025 [6]. A look at the conditions of the calibration, laid down in the calibration certificate, is crucial here. The suitability of a measuring device for the potentially complex measurement purpose is the central challenge in radiation protection today.

Once again, radiation protection is facing a technological challenge, which cannot be resolved by a single person or organisation due to its complexity. This means that we need to look for new solutions.

## 1.2. Radiation protection in EURAMET

One such solution could be a European Metrology Network (EMN) for radiation protection. It could act as a central point of contact to collect and analyse all metrological needs related to radiation protection and thus ensure coordinated and reliable quality assurance in Europe.

In 2018, a project consortium was formed to prepare an EMN on radiation protection: This preparatory project EMPIR 19NET03 supportBSS currently pools the expertise of 16 national metrology institutes (NMIs) or designated institutes (DIs) from Germany, France, the Czech Republic, Italy, Poland, Romania, Bosnia and Herzegovina, Croatia, Portugal, Slovenia, the United Kingdom, Belgium, Sweden, Serbia and Finland.

The EMN for Radiation Protection has been officially approved by the EURAMET General Assembly on 7 June 2021. Expansion of the membership is expressly desired. With the central support of EURAMET, it brings the expertise of its members (NMI and DI) and partners together and works to provide a common platform for their services. One of its most important tasks will be to give the metrology of radiation protection a strong voice in Europe in order to be able to accompany technological development responsibly.

EURAMET's vision is to ensure that Europe has world-leading metrology expertise based on high-quality scientific research and an effective and inclusive infrastructure that meets the rapidly growing needs of end users.

The metrology networks do this very directly: they bring the metrology institutes together with the users of metrology. For the first time, the metrology umbrella organisation includes direct partners from non-metrology institutes. In the case of the EMN RP, these first partners are: the German Federal Office for Radiation Protection (BfS), the European Radiation Dosimetry Group EURADOS e.V., the Polish Central Laboratory for Radiological Protection (CLOR) and a company, Eckert & Ziegler Nuclitec GmbH.

## 1.3. Vancouver call for action to strengthen expertise in radiation protection worldwide

Radiation protection is a worldwide challenge. Metrology plays an important role here, but worldwide requirements need worldwide partnership. The International Commission on Radiological Protection (ICRP) is an independent Registered Charity, established to advance for the public benefit the science of radiological protection, in particular by providing recommendations and guidance on all aspects of protection against ionising radiation. ICRP signed a letter of intent with EURAMET in 2022 and since then the EMN RP supports ICRP activities and vice versa. ICRP calls for action to strengthen expertise in radiological protection worldwide through:

1. National governments and funding agencies strengthening resources for radiological protection research allocated by governments and international organisations.

2. National research laboratories and other institutions launching and sustaining long-term research programmes.

3. Universities developing undergraduate and graduate university programmes and making students aware of job opportunities in radiation-related fields.

4. Using plain language when interacting with the public and decision makers about radiological protection.

5. Fostering general awareness of proper uses of radiation and radiological protection through education and training of information multipliers.

The EMN RP supports these statements directly. EURAMET provides with its research programmes (EMPIR in the past, now the European Partnership on Metrology) excellent funding possibilities for research and development related to ionising radiation. The Metrology Partnership brings together the measurement science community and stakeholders to deliver on global challenges including health and climate, support the European Green Deal, and underpin innovation in industry through collaborative research. Moreover, radiation protection can benefit from technological trends funded in cross border projects in the digital transformation call.

The Partnership on Metrology has instruments to support capacity building across Europe and exchange of experts between research institutes. Funding instruments cover also regulatory aspects and development of international standards. In these projects, the stakeholder interaction is at the focus for two-way exchange of ideas and information and to provide the end-users support in adapting new regulations and practices.

# 2. New capacities: services and knowledge transfer

## 2.1. New calibration services by National and European Research

A first example for the successful establishment of new capacities is the national German project "Establishment and characterisation of a reference field for ensuring radiation protection at accelerator facilities in medicine and research and for testing and calibrating of corresponding measuring instruments". Type-testing is usually performed with energies up to 7 MeV in continuous radiation fields. As the response of radiation protection dosemeters can be affected by pulsed radiation,
e.g. due to dead time effects, the international standards for testing dosemeters in pulsed fields of ionising radiation (ISO/TS 18090-1 and IEC TS 63050) were established. However, a reference field similar to the fields typically expected behind (weak) shieldings of medical accelerators was non-existent. Within the mentioned project, after the gap analysis of EMN RP [7], such a reference field has been funded by BMUV and afterwards established by PTB. Within this characterized pulsed photon reference field, dose rates occurring behind (insufficient) shielding of medical and research accelerator facilities can be realized. The field is based on a commercial medical linear accelerator at PTB. It is generated behind a 2 m-thick concrete wall with a composition typical used for radiation shielding.

A second example is the outcome of a European metrology project: new radioactive sources, devices and innovative calibration procedures [8] have been developed within EMPIR 19ENV01 traceRadon. Radon gas is the largest source of public exposure to naturally occurring radioactivity. It is considered as the second highest risk for developing lung cancer.

Normally, the emanation (i.e. the radon activity released) of a source is determined by measuring the activity of the radon progeny remaining in the radium source. With the low activities required for environmental measurement, the highest detection limit and lowest uncertainties are required: An ion-implanted silicon semiconductor detector is coated with radium chloride by thermal vapour deposition directly onto the dead layer of the detector. This means that the detector itself is the source of the radon. At the same time, it is the spectrometric detector for the resulting alpha radiation. It measures the decay of the radium as well as that of the radon and its progeny.

With the application of this new type of traceability radon measurements becomes also feasible for application in the climate observation networks, such as the European Integrated Carbon Observation System (ICOS). Data on radon activity concentrations in the atmosphere and on radon fluxes from the ground are validated in the metrological sense and are therefore comparable with each other (from station to station). In addition, the flux and atmospheric measurements offer the opportunity to improve the mapping and designation of radon priority areas throughout Europe. This is one of the costliest areas of radiation protection, as it was imposed on all European member states in Directive 2013/59/Euratom for mandatory implementation into national law. The project provided new approaches to determine so-called Radon Priority Areas to channel the investments regionally and on a trustworthy scientific base. It linked climate observation and radiation protection for the first time [9].

A third example addresses the radiological emergencies when alpha emitters are freed. A detection system to measure large-scale contamination of these radionuclides was not available and new remote detection techniques which overcome shortcomings of traditional detectors were needed.

As part of the EMPIR project 19ENV02 RemoteALPHA, the remote and real-time detection of α-emitting radionuclides was realized using the so-called α radioluminescence technique [10]. This technique is based on the ultraviolet (UV) luminescence of air, so-called radio-luminescence, which is caused by the interaction of α-particles with the air, especially the nitrogen it contains. The main advantage of this technique arises from the fact that this UV light can be transmitted through the air over a considerable distance (hundreds of metres), which is several orders of magnitude greater than the range of α-particles in the air (a few centimetres). The optical detection systems integrated in Unmanned Aircraft Systems (UAS) enables remote detection of contaminated areas, reducing detection costs, time and risk to personnel and enabling automated scanning.

## 2.2. Capacity building

EMN RP has established several activities to support capacity building. For 2023, three international activities can be named as an

example to show the variety of what it can provide: a trainings course, pilot study and training intercomparison.

The training course "Dosimetry and Emergency Preparedness" was held as an outcome 19NET03 supportBSS in cooperation with EURADOS WG2 Harmonization of Individual Monitoring in Europe, hosted by the Greek Atomic Energy Commission (EEAE) in Athens in September 2023. The aim of this joint course was to cover the theoretical background of handling emergencies and to expand it with practical measurement exercises. This training course provided three days of lectures and discussions in combination with one day of practical exercises in small groups of about five persons.

The second example is an intercomparison was organised with two aims: To provide traceability for the EURADOS intercomparison IC2023calib for calibration and test laboratories and to show, that the EMN RP is able to organise lower-level intercomparisons, which could be used to support ISO 17025 accreditations. It is important to understand that these type of intercomparison is not in a Technical Committee announced and agreed (here EURAMET TC-IR) but has comparable metrological procedure. Therefore, this intercomparison was setup as a so-called pilot study for intercomparison of passive dosemeters, the comparison quantity was $H^*(10)$, the radiation qualities were N-30, N-150, S-Cs and S-Co and the participants were not restricted to be NMI or DI.

The third example is a training intercomparison providing hands-on training in the intercomparison of radiation protection quantities (air kerma, $H^*(10)$) using secondary standards (transfer ionisation chambers). It was aimed at NMIs and DIs from emerging countries in order to support performing intercomparisons in accordance with the new ISO 4037 standard. It was performed by Vinča institute in Belgrade, Serbia in September 2023.

## 3. Reaching out towards Euratom

EMN RP provides guidance to European developments in radiation protection. Within Europe the Euratom treaty has a rather independent role: Euratom is a community established under the Euratom Treaty establishing the European Atomic Energy Community. Parties to the Euratom are the EU Member States. The EU and Euratom share a common institutional framework, a common budget and common financial provisions. Liabilities of Euratom are covered by the EU budget and Euratom. Loans to third countries are in addition covered by the Guarantee Fund for External Actions. As a separate legal entity, Euratom has its own credit ratings. These are identical to those of the European Union.

Currently Euratom research and training programme for 2026–2027 is proposed: It concerns research and training activities in nuclear fusion and fission. It is a direct continuation of the current research and training programme (2021–2025), which complements the Horizon Europe framework programme for research and innovation. The Euratom programme aims to maintain the highest nuclear safety standards and Europe’s competences in the nuclear domain.

EMN RP published two fundamental statements to support to general aspects in the Euratom research and training programme.

**Statement 1:** Establish a mechanism that implements quality assurance and traceability to the SI system by ensuring metrology participation as a matter of course.

The reasoning behind this is that EMNs under EURAMET play a key role in the further development of research, technology, standardisation, and regulation in Europe. Their role is that of an anchor of trust for the quality of research results and research data. This requires a mechanism that makes this role possible in Euratom: just as it is a matter of course in every research project today that data is FAIR and publications are open access, a mechanism for quality must be implemented that ensures metrology participation. This transformation process can be promoted through suitable framework conditions within Euratom research funding and could be discussed and supported by EMN RP. As a result, the
<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Scheme on how metrology supports radiation protection and the relevant radiation protection legislation. The regulation is given in yellow at the top and red and green at the bottom of the figure. The contribution of metrology is represented in grey and white including the white arrows. Practices and activities making use of metrological services (in blue) that need to show compliance with the regulations mentioned in topic 5 are represented in orange [12].</figcaption></figure>

quality of research results would improve, and the implementation of results would become faster and cheaper. In addition, discussions about new technologies could be (more) fact-based. In radiation protection, such objectification would reduce bureaucracy and enable resources to be channelled towards the challenges. Further, such an approach would enable widening countries to participate in effective knowledge transfer to effectively implement radiation protection legislation in today's quickly changing environment.

**Statement 2:** Establish a mechanism that implements participation in standardisation as a prerequisite for funding within Euratom Calls.

Here the reasoning is, that the aim must be to harmonise approaches internationally. This also includes clear quality criteria, defined in norms and standards that protect the population and enable new technologies. The transformation process of digitalisation through the provision of digital conformity assessments, digital calibration certificates and the digital product passport, for example, can be a decisive building block here. In the field of technical standards, European involvement is declining. There is increasingly less involvement from the member states within the framework of CEN-CENELEC and ISO and IEC. The reasons for this are: It is a time-consuming commitment that ties up personnel, many years of expertise are required of the person involved and it is a cost-intensive activity for the engaging organisation. As a result, Europe is increasingly playing a minor role in standardisation. This is a serious disadvantage for European interests because those who do not standardise will be standardised. The consequences to European industry can be overwhelming.

Measures are needed to make participation from Europe in international standardisation attractive (again) for those concerned. The rules of technology, as laid down in the standards, should be the basis for legislation. Thus, the standardization should not be driven by economics and industry only – safety, reliability and applicability should be driving forces, too. Bureaucratic obstacles should be avoided and established tools that ensure trust in the quality and safety of new technologies

should be supported and digitalised in a targeted manner.

## 4. Conclusions

The increased risk awareness in the society sets stringent quality requirements on the data on which our knowledge on radiation risks is based. Measurements and modelling of exposure to ionising radiation and its consequences depend on the accuracy and representativeness of the underlining basic physical, chemical and biological data. At the same time, new quantities are proposed with the aim to more accurately take into account the properties of the exposed individuals. Measurement and calibration services must be developed for these quantities, and they must be easily available for the end users.

Metrology and EMN RP supports this ongoing transformation by providing a sound basis for measurements and modelling. Availability of appropriate standards and metrology services, such as measurements and radiation protection instrument calibrations, create a basis on which reliable radiation exposure estimates can be based on. At the same time the European Partnership on Metrology brings together metrology community and its stakeholders to tackle global challenges in fundamental science and applications of ionising radiation, including health, environment, and industrial applications. For this reason, public consultations have been established to shape the Calls within the Partnership of Metrology. Metrology for Regulation - Open Public Consultation [11]. Previous consultations took place in 2022 and 2023 flanked by a consultation on PIANOFORTE needs and information sharing.

EMN RP was successful in supporting the Partnership projects in the normative field in the Call 2022: Harmonization, update and implementation of standards related to radiation protection dosimeters for photon radiation (22NRM07 GuideRadPROS) and Traceability in medical X-ray imaging dosimetry (22NRM01 TraMeXI). The consultation of EMN RP within the Call 2023 (Industry) resulted to the project "Radon metrology: Sensor networks for big buildings and future cities".
EMN RP comprehensively underpins by this the metrological quality infrastructure for radiation protection and legal dose assessment [12], see Fig. 1. It maintains a constructive dialogue and liaison between metrology institutes, calibration and test laboratories, proficiency testing and the stakeholders of radiation protection regulation, formally integrate existing reference laboratories into the EMN infrastructure and develop a joint strategy to identify and prioritize measurands. New radiation protection principles and quantities require knowledge sharing, development of new services and building new expertise. EMN RP provides by this solution for the quality infrastructure and strengthens the economy and cohesion of Europe.

## Acknowledgments

The supportBSS project was launched in summer 2020 and the EMN for Radiation Protection started its work in June 2021. The EMN is supported by a broad global scientific community from the fields of radiation protection and metrology. At this point, the outstanding support and cooperation of the ICRP, BIPM, TC-IR and IAEA should be mentioned. All stakeholders are united by the goal of providing new and improved data and services for science, industry, the public and decision-makers.

Setting up a new structure on this scale is a major challenge, as it affects the strategic interests of research institutions, ministries and member states. From the members' point of view, the network is absolutely essential. It is the only way to support the introduction of new technologies with metrology in the long term, to enable their use quickly and safely and to generate a common European understanding in their use.

Therefore, many thanks go to EURAMET e.V., which made such a project possible in the first place with the EMPIR framework programme and such a structure with its European Metrology Networks initiative. 19NET03 supportBSS, 19ENV01 traceRadon and 19ENV02 RemoteALPHA have received funding from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme.

The national German reference field project was funded by the Bundesamt für Strahlenschutz https://www.bfs.de; project no. 3619S2236.

The authors would like to express thanks to the research involved in the named projects and welcome our new member from National Metrology Institute of the Republic of Moldova (INM-MD) and new partner from Danish Health Authority currently joining the EMN.

## References

[1] R.H. Clarke, J. Valentin, The history of ICRP and the evolution of its policies, in ICRP Publication 109, Ann. ICRP 39 (2009) 75-110, https://doi.org/10.1016/j.icrp.2009.07.009.

[2] Council Directive 2013/59/Euratom of 5 December 2013 Laying Down Basic Safety Standards for Protection against the Dangers Arising from Exposure to Ionising Radiation, 2013. CELEX number: 32013L0059, https://eur-lex.europa.eu/legal-content/DE/TXT/?uri=CELEX%3A12012A%2FTXT.

[3] The International Commission on Radiological Protection 80th Anniversary: The evolution of its policies through 80 years. In: Gallego, E., Pérez, M., Beatriz, G. (Eds.), Strengthening Radiation Protection Worldwide, IRPA XII Congress. Available at: http://www.irpa12.org.ar/index.php.

[4] Treaty establishing the European Atomic Energy Community, established the European Atomic Energy Community, signed on 25 March 1957. CONSOLIDATED

VERSION, ISBN 978-92-824-5085-7. DOI: https://eur-lex.europa.eu/legal-content/DE/TXT/?uri=CELEX:12012A/TXT.

[5] Joint Committee for Guides in Metrology, International Vocabulary of Metrology - Basic and General Concepts and Associated Terms (VIM), 2012, https://doi.org/10.1515/ci.2012.34.3.26.

[6] DIN EN ISO/IEC 17025:2018-03: Allgemeine Anforderungen an die Kompetenz von Prüf- und Kalibrierlaboratorien (ISO/IEC 17025:2017).

[7] B. Khanbabaee, et al., Support for a European metrology network on reliable radiation protection: gaps in radiation protection and related metrology, RAD Conf. Proc. 5 (2021) 21-27, https://doi.org/10.21175/RadProc.2021.04. ISSN 2466-4626.

[8] A. Röttger, et al., Metrology infrastructure for radon metrology at the environmental level, ACTA IMEKO 12 (2) (June 2023) 1-7, https://doi.org/10.21014/actaimeko.v12i2.1440. ISSN: 2221-870X.

[9] A. Röttger, et al., New metrology for radon at the environmental level, Meas. Sci. Technol. 32 (2021) 124008, https://doi.org/10.1088/1361-6501/ac298d.

[10] F. Krasniqi, et al., Standoff UV-C imaging of α-particle emitters, Nucl. Instrum. Methods Phys. Res. 987 (2021), https://doi.org/10.1016/j.nima.2020.164821.

[11] EURAMET Website: https://www.euramet.org/publications-media-centre/event/s/detail/event/metrology-for-regulation-open-public-consultation-online-event.

[12] J. Alves, et al., Metrology supporting the European regulation for radiation protection, Radiat. Protect. Dosim. 200 (2) (2024) 155-163, https://doi.org/10.1093/rpd/ncad289.

Annette Röttger<sup>a, *,</sup> Britt Wens<sup>b</sup>, Amra Sabeta<sup>c</sup>, Robert Bernat<sup>d</sup>, Vladimír Scochor<sup>e</sup>, Teemu Siiskonen<sup>f</sup>, Christelle Adam-Guillermin<sup>g</sup>, Attila Veres<sup>h</sup>, Massimo Pinto<sup>i</sup>, Michal Derlacinski<sup>j</sup>, João Henrique Garcia Alves<sup>k</sup>, Mihail-Razvan Ioan<sup>l</sup>, Miloš Živanović<sup>m</sup>, Denis Glavič-Cindro<sup>n</sup>, Linda Person<sup>o</sup>, Steven Bell<sup>p</sup>, Sebastian Feige<sup>q</sup>, Filip Vanhavere<sup>b, k</sup>, Katarzyna Woloszczuk<sup>r</sup>, Victor Vicente-Vilas<sup>t</sup>

<sup>a</sup> Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany

<sup>b</sup> Nuclear Calibration Laboratory, Belgian Nuclear Research Centre (SCK-CEN/LNK), Belgium

<sup>c</sup> Institute of Metrology of Bosnia and Herzegovina (IMBiH), Bosnia and Herzegovina

<sup>d</sup> Ruder Boskovic Institute - Secondary Standard Dosimetry Laboratory (IRB-SSDL), Croatia

<sup>e</sup> Cesky Metrologicky Institut, Czech Republic

<sup>f</sup> Radiation and Nuclear Safety Authority (STUK), Finland

<sup>g</sup> Institut de Radioprotection et de Sûreté Nucléaire, France

<sup>h</sup> Laboratoire National Henri Becquerel/Commissariat à l'Energie Atomique, France

<sup>i</sup> Agenzia Nazionale per le nuove tecnologie, l'energia e lo sviluppo economico sostenibile, Italy

<sup>j</sup> Central Office of Measures (GUM), Poland

<sup>k</sup> IST/LPSR - Laboratory for Radiation Protection and Safety, Portugal

<sup>l</sup> Institutul National de Cercetare-Dezvoltare pentru Fizica si Inginerie Nucleara "Horia Hulubei", Romania

<sup>m</sup> Vinca Institute of Nuclear Sciences - National Institute of the Republic of Serbia, University of Belgrade, Serbia

<sup>n</sup> Metrology Institute of the Republic of Slovenia, Jožef Stefan Institute, Slovenia

<sup>o</sup> Swedish Radiation Safety Authority, Sweden

<sup>p</sup> NPL Management Limited, UK

<sup>q</sup> Bundesamt für Strahlenschutz, Germany

<sup>r</sup> European Radiation Dosimetry Group (EURADOS e.V.), Europe

<sup>s</sup> Central Laboratory for Radiological Protection, Poland

<sup>t</sup> Eckert & Ziegler Nuclitec GmbH, Germany

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: annette.roettger@ptb.de (A. Röttger).</footnote>