Individual Monitoring Services Research Articles

Overview and current challenges at the Calibration Laboratory of the Paul Scherrer Institute

The Calibration Laboratory of the Paul Scherrer Institute (PSI) is a secondary calibration laboratory accredited by the Swiss Accreditation Service (SAS) in accordance with ISO 17025. It also acts as a verification body authorized by the Swiss Federal Institute of Metrology (METAS). The Laboratory is equipped with X-ray, gamma and neutron irradiation facilities, providing characterized reference radiation fields for gamma 137Cs, 60Co, narrow spectrum X-rays from N-15 to N-300 and neutron radionuclide sources 252Cf, 252Cf (D2O-moderated) and 241Am-Be. The laboratory performs routine calibrations, organizes intercomparison measurements for individual monitoring services in Switzerland, and participates in various research projects, e.g., by performing irradiations in reference fields. For this reason, the proper characterization of reference radiation fields is of utmost importance for ensuring high quality irradiations and calibrations of personal dosemeters and radiation protection instruments. In this contribution, we provide an overview of the irradiation facilities at the Calibration Laboratory at PSI and discuss the challenges of characterizing reference radiation fields. In particular, we will discuss the factors affecting the determination of the distance between the source and irradiated dosemeters and detectors, as well as issues related to 252Cf decay and contribution of 250Cf. We will also demonstrate the use of Monte-Carlo simulations in determining the optimal position of the source and irradiation facility within the irradiation room.

Results from 2023 interlaboratory comparison in Southeast and East Asia on OSL personal dosimeter performance in photon fields

The intercomparison of personal dose equivalent (Hp(10)) among nine economies was carried out at 27 Individual Monitoring Service (IMS) Laboratories in Southeast and East Asia in 2023. In this programme, a whole-body dose assessment from Cs-137 and N-80 X-rays with two different incident beam angles (0 deg and 30 deg) was performed using an Optically Stimulated Luminescence (OSL) dosimeter. The trumpet curve recommended by IAEA GSG-7 was used as the criterion of acceptance value. The results showed that 95% of all data were within the acceptable value, with 13 items of data from two laboratories being unacceptable. After the intercomparison programme was concluded, these two laboratories implemented system improvement, including reader performance checks, calibration, configuration adjustment, and dose evaluation method enhancement. The results after improvement fell within the acceptable limit, indicating successful system enhancement. This study contributes to the harmonisation of individual monitoring service laboratories in Southeast and East Asia, ensuring that measurement results are traceable to the International System of Units (SI). Each laboratory fulfils the performance standard requirements to ensure the validity of the results for the individual monitoring service laboratory. Moreover, the complementary study induced by this exercise indicates the necessity of the intercomparison programme and successful outcome of the system improvement.

EURADOS intercomparison for whole-body neutron dosemeters from 2012 to 2022

Within the EURADOS (European Radiation Dosimetry Group) self-sustained programme of regular intercomparisons (ICs) for individual monitoring, three campaigns had been performed in 2012, 2017 and 2022 to assess the performance of neutron personal dosemeters routinely used to measure personal dose equivalent, Hp(10). The irradiation schemes were established to provide participants with useful information regarding linearity, reproducibility and response of their dosimetry systems at different energies and angles of incidence. Small alterations were made in irradiation plans for subsequent exercises. Combinations of standard calibration fields and simulated workplace fields were employed, using bare and moderated neutron sources as well as monoenergetic and thermal neutron fields. Neutron energies used to evaluate dosemeter performance ranged from thermal to several MeV. Dose values varied between 0.3 mSv and 15 mSv. The number of participating laboratories in the three campaigns was stable: 31 in IC2012n, 32 in IC2017n and 29 in IC2022n. The dosimetry systems could have been categorized according to their detection principle into albedo and track dosemeters, or a combination of both. In 2012, a category ‘other’ had to be introduced to consider active personal dosemeters and fission track detectors. In 2012, participants were asked to provided results in a two-step procedure: (i) with no information on the radiation fields, and (ii) after receiving additional simplified a priori information on the energy distribution of the neutron fields to enable correction for dosemeter response. In 2017 and 2022, based on a one-step procedure, however, participants might have requested a priori information upon registration, which was reported in the certificate of participation. Intercomparison results were analysed against the acceptance criteria of the ISO 14146:2018 standard, although there were no standardized performance requirements for neutron personal dosemeters at the time of IC2012n. The paper compares the results of the three exercises, identifies major problems for individual monitoring services and shows trends in dosimetric performance. In all three intercomparisons, a few systems had shown problems related to calibration. Data do not allow to draw a universally applicable conclusion with regard to potentially superior performance of one particular dosimetry system.

EURADOS ISO/IEC 17025 guidance for IMS: suggestions on how to interpret and implement the requirements including examples from accredited laboratories.

Individual monitoring of external radiation is an activity usually regulated by national regulatory bodies in most countries. Regulations generally contain technical requirements to be met by the individual monitoring services (IMS), in order to ensure that the measurements are correct and therefore the dosimetry results are reliable. In some countries, the requirements include or even consist of the accreditation of the service according to the standard ISO/IEC 17025: 'General requirements for the competence of testing and calibration laboratories.' It is a fact that accreditation is a growing trend among European IMS as a way to guarantee confidence in their technical competence. The acceptance of the dosimetry results between countries and their indentation in the respective National Dose Registries is facilitated if laboratories conform to the ISO/IEC 17025 standard. In the framework of the activities of EURADOS (European Radiation Dosimetry Group) working group 2 'Harmonization of Individual Monitoring in Europe' and attending to the concern of many European IMS in the process of accreditation, a guide has been prepared. The purpose was to assist and encourage IMS to apply for accreditation and to share the authors' own experience with the process. The guide intends to be a practical reference for IMS on how to interpret and implement the ISO/IEC 17025 requirements to the specific activity of a personal dosimetry service for external radiation, emphasizing those aspects of special interest. It includes examples from dosimetry laboratories already accredited. The major novelties from a new edition of ISO/IEC 17025: 2017 are also identified in the guide. Finally, the guide aims to assist the auditing process, giving examples of auditor's questions and how to show evidence of compliance. The main findings are presented.

Revision of the 21909 standard on passive personal neutron dosemeters.

Since 2012, International Standardization Organization TC85/SC2 Working Group 19 dealing with 'Individual monitoring for external radiations' has been conducting important work revising the 21909 standard on passive personal neutron dosemeters. A consensus in the community acted that the 2005 version( 1) needed to be revised for two main reasons: (1) to achieve a document applicable to all systems irrespectively to the considered techniques and (2) to reach harmonisation between performance tests and conditions of use at the workplaces. The document was completely rewritten to be binding enough to ensure that any neutron dosimetry system fulfilling the criteria would be reliable in most of the usual work situations, in terms of dose level, energy and direction distributions of the neutron fluence. This paper explains the reasons behind the revision and the new philosophy of the series published in 2021, so that Individual Monitoring Services may better understand how to apply the requirements in practice.

The EURADOS CR-39 Quality task for the optimisation and harmonisation of personal neutron dosimetry with CR-39 (PADC).

CR-39 (PADC) nuclear track detectors are among the most widespread devices used for personal neutron dosimetry; however, some issues related to the variable material quality of the CR-39 polymer hinder the performance of CR-39-based dosemeters. For this reason, the Working Group 2 (WG2) of the European Radiation Dosimetry Group (EURADOS) has recently launched the CR-39 Quality task, a project aimed at improving and harmonising personal neutron dosimetry with CR-39 in Europe. Whitin this task, a close collaboration among researchers, individual monitoring services and dosemeter grade CR-39 manufacturers is achieved, thus facilitating the direct dialog between producer and consumer to reach an optimised material for personal neutron dosimetry applications.

EURADOS intercomparison IC2020ph on whole body dosemeters for photons.

The European Dosimetry Group has been organising international intercomparisons (ICs) for personal dosemeters on a regular basis. The IC announced in 2020 was postponed to the end of 2020 and the beginning of 2021 due to coronavirus (COVID-19) restrictions. The irradiation plan consisted of nine irradiation setups with five different photon radiation qualities (S-Cs, S-Co, N-150, W-60, W-80) and two different angles of irradiation incidence (0o and 60o). A total of 112 monitoring services from 50 countries with 132 dosimetry systems participated. The present work describes and analyses the individual results for the personal dose equivalent quantities Hp(10) and, if submitted, Hp(0.07) for all participating systems. It also presents the organisational details and the difficulties arising from the COVID-19 crisis during the IC. The statistical results showed a satisfactory performance with the medians of all Hp(10) and Hp(0.07) response values very close to unity. However, there are few individual monitoring services with significant large variations.

Optimization of calibration interval based on equipment metrological history.

The purpose of this paper is to describe a method for optimizing the calibration period of a dosimetry measurement system with a focus on the personal dose equivalents Hp(d) and individual monitoring services. The systematic and analytical method developed provides a justification to the calibration interval based on experimental data and measurement uncertainties. Its main input is the metrological history of the equipment that is then used to predict the drift of the measurement system. The method is used to make the calibration operation more efficient over time in terms of cost and metrology. After a description of the method itself, the example of the OSL dosemeter reading process will be discussed and results will be shown. The method developed may be applied to other measurement processes no matter the technology used.

Personal dosimetry at the Paul Scherrer Institute.

The Paul Scherrer Institute (PSI) is the largest research institute for natural and engineering sciences in Switzerland. PSI develops, builds and operates complex large research facilities. Every year, >2400 scientists from Switzerland and around the world come to PSI to use the facilities and to carry out experiments. Many areas at PSI are radiation protection areas. Depending on the radiation protection area, the work carried out and the time the users spend in these areas, they have to carry a personal dosemeter. PSI runs an individual monitoring service in compliance with the Swiss legislation on radiological protection and approved by the Swiss Federal Nuclear Safety Inspectorate. The service provides about 35000 dosemeters per year for the internal and external customers consisting of whole-body dosemeters for photons and neutrons as well as extremity dosemeters. This paper gives an overview on the employed personal dosimetry techniques by the individual monitoring service of PSI, the number of distributed dosemeters for internal and external customers and statistics about the measured doses at PSI over 30years.

Analysis of EURADOS neutron intercomparison results according to new ISO standards criteria.

The European Radiation Dosimetry Group has carried out several different types of intercomparison (IC) exercises in the past that qualify as proficiency tests for different dosimetry systems and types of radiation. The first neutron dosemeter IC was held in 2012 (IC2012n) and was followed by a second in 2017/2018 (IC2017n). In sum, 31 Individual Monitoring Services (IMSs) entered 34 dosimetry systems in IC2012n, and 32 IMSs entered 33 dosimetry systems for IC2017n. Such exercises provided a rare opportunity to see how neutron dosemeters perform. For the IC2012n exercise, there were no applicable performance standards for neutron personal dosemeters. ISO/TC85/SC2 updated the ISO Standard 14146 in 2018 (ISO 14146:2018. Radiation protection-Criteria and performance limits for the periodic evaluation of dosimetry services) to include neutron dosimetry. It was thus possible to analyse the IC2017n exercise in accordance with the requirements given by this new standard. It is now of interest to reanalyse the results of IC2012n to quantify any modifications to the conclusions.

EURADOS intercomparisons on whole-body dosemeters for photons from 2008 to 2020: analysis and comparison of general results.

Starting in 2008 the European Dosimetry Group (EURADOS) has been performing international intercomparisons (ICs) on photon whole-body dosemeters for individual monitoring services. These ICs have been organized (on a biennial basis) starting 2008 up to 2020 now, each time with a similar set-up but with small alterations in the subsequent irradiation plans. The response for Hp(10) and Hp(0.07) was tested for different radiation qualities, angles of incidences (0°-60°) within a wide range of dose values (0.5-500mSv), to check energy and angular response, linearity, reproducibility and mixed-field response. Within the last 12years almost 15 000 whole body dosemeters have been irradiated and the corresponding response values evaluated. With an increasing number of participants and participating systems (from 62 to 132), this IC program has become an important tool for individual monitoring services to test their whole-body dosimetry systems, compare their results with other services or systems and to improve the quality of their dosimetry. The paper presents and compares the general results of these seven ICs and analyses the dosimetric results for the participating system types.

Results and analysis of an intercomparisons study for individual monitoring services of Latin American and Caribbean regions.

The aim of this paper is to present the results obtained by the Latin-American and Caribbean personal dosimetry services that participated, with the support of IAEA, in the 2020-Eurados whole-body dosemeter intercomparison for photon radiation. All participant services in this study use thermoluminescent dosimetry (TLD) systems except one that uses optically stimulated luminescence (OSL) dosemeters. Data analysis shows that 93.4% of the results are within the acceptance range, according to International ISO Standard ISO 14146: 2018. The evaluation of the trumpet curves shows that only three laboratories presented a few dosemeters results outside the limits of acceptability. Participation in this Eurados intercomparison exercise gave the Latin American and Caribbean laboratories the opportunity to show compliance with their own quality management system, to compare results with other participants and to develop plans for improving their dosimetry systems. It also gave the assurance that occupational doses are being measured properly and following the international standards in the regions.

Assessment of the impact on a PADC neutron dosimetry system of the new operational dose quantities proposed in ICRU report 95.

The International Commission on Radiation Units and Measurements, ICRU, have recommended, in ICRU Report 95, the adoption of new operational quantities for use in radiation protection monitoring. Their implementation will pose problems for instrument manufacturers supplying area dosemeters and for individual monitoring services providing personal dosemeters for radiation workers. The problems arise for photon, neutron and beta dosimetry, but this paper deals solely with neutron personal dosemeters based on poly-allyl diglycol carbonate (PADC) plastic. It presents information on the problems to be expected based on data from calibrations of actual personal neutron dosemeters in terms of the existing dose quantities.

Type-testing of the TLD system used for the assessing the eye lens doses due to ionising radiation

Individual monitoring service at the Department for Radiation and Environmental Protection of Vinca Institute of Nuclear Sciences performs individual whole-body and extremities monitoring of exposed workers, using thermoluminescent dosimetry (TLD) method. The dosemeters for eye-lens personal dose equivalent measurements, Hp(3), are not regularly used at the workplaces in Serbia, even though the individual monitoring method is accredited and available at the dosimetry service. Type testing of Hp(3) dosemeters based on LiF: Mg,Ti, placed in modified ring holders was done following the changes in ISO 4037:2019 and IEC 62387:2020. The type testing was done by varying radiation-based influence quantities: photon energies ranging from 33.3 keV up to 1.25 MeV, angle of incidence values of 0°, 45°, 60°, 75°, dose range from 0.05 mSv to 10 Sv. The results show that the passive dosimetry monitoring system satisfies IEC 62387:2020 requirements in the mandatory range of influence quantities, except for the lowest tested energy of 33 keV, when incident radiation angle is ±60° and higher.

Assessment of occupational exposure in medical practice in Gabon during 2013–2020

ObjectiveTo evaluate whole-body, extremity and eye-lens occupational dose equivalents of ionizing radiation to Occupationally Exposed Workers (OEWs) in Gabon, monitored by the national Individual Monitoring Service (IMS), in the medical practice. MethodsA total of 816 dose records for 205 OEWs were evaluated. Doses were collected for an eight-year period, from 2013 to 2020. Twelve public and private hospitals were involved, including a cancer centre where radiotherapy (RT) and nuclear medicine (NM) procedures are regularly performed. OEWs were monitored, on a monthly or quarterly basis, for whole-body dose and extremity dose using an optically stimulated luminescence (OSL) dosimeter worn on the torso or the wrist, as appropriate. Eye-lens dose was estimated from whole-body dose results. ResultsThe whole-body dose distribution was skewed and the zero dose was associated with a probability of 47%. Some recorded doses were associated with estimated X-ray energies above those typically encountered in diagnostic radiology, thus suggesting that some doses attributed to workers and believed to be due to X-rays may in fact be due to background radiation (false positive dose records). For the period 2013–2020, annual doses to OEWs in diagnostic radiology (DR), NM and RT departments were 0.40 ​mSv, 0.38 ​mSv and 0.09 ​mSv, respectively. For the same period, the mean annual extremity and eye-lens doses were 0.78 ​mSv (range: 0–5.24 ​mSv) and 0.35 ​mSv (range: 0–3.74 ​mSv), respectively. ConclusionWith little effort by the national IMS and the regulatory body, annual whole-body doses to workers can be kept well below 6 ​mSv, thus efficiently contributing to the optimization of worker's protection. However, extremity doses may in fact be greater than those reported for OEWs in the NM department. Finally, eye-lens doses were well below the new annual dose limit of 20 ​mSv, thus demonstrating that, in the current situation, OEWs in the NM department do not require routine eye lens dose monitoring. Rather, whole-body dose may be used as an indicator of eye-lens dose.

Neutron personal dosimetry using polyallyl diglycol carbonate (PADC): Current status, best practices and proposed research

The objective of this paper is to provide an overview of the current status in neutron personal dosimetry based on poly allyl diglycol carbonate (PADC), also commonly known by the commercial name CR-39, to summarize the best practices in the field, and to point future research directions. An overview of the fundamentals of the technique is given, including a discussion on the PADC material, main parameters and characteristics, practical considerations, dosimetry approaches, and relevant standards. This work also summarizes the best practices adopted by individual monitoring services (IMSs) and discusses the research needed to improve the performance of this type of neutron dosimetry technique, as well as the challenges that make progress difficult. This work is based on the knowledge and experience of several laboratories and investigators and is part of the activities of the European Radiation Dosimetry Group (EURADOS) Working Group 2 –Harmonization of Individual Monitoring in Europe (WG2).

Results of type testing of MTS-N dosimeters with IEC 62387:2012 standard at the laboratory of external dosimetry in Nicaragua

This study presents the results of the verification of the method according to working procedures of the Laboratory of External Dosimetry (LDE) located at the Laboratory of Radiation Physics and Metrology (LAF-RAM), which is the only Individual Monitoring service provider in Nicaragua. The test is considered as validation of the method since the LAF-RAM follows a Quality Management System. The chosen performance testing according to IEC 62387:2012 are Coefficient of variation, Non linearity, Radiation energy and angle of incidence, Dosimeter droop, Light exposure (reader), Over-response of radiation incidence and Build up, fading, self-irradiance and natural radiation response. The results in general show that all test are in compliance with the requirements except for some temporal conditions in Buildup, fading, self-irradiance test.

On ISO 21909–1:2015 and the metrological performance of the Landauer Neutrak-T dosemeter

Personal dosimetry for ionizing radiation is a regulated activity in Europe. More particularly, in France Individual Monitoring Services (IMS) are required to be accredited against ISO/IEC Standard 17025 (ISO 17025:2017) for the personal dose equivalent measurements they perform. In the field of external personal dosimetry for ionizing radiations, there are no standardized methods for routine measurements of participants' personal dose equivalent. Instead, the standards focus on defining protocols and associated acceptable performance limits for testing the measurement process. ISO Standard 21909 is the one related to passive neutron dosimetry systems. This standard has been completely revised and its newest version was published in 2015. The two versions of the standard differ in terms of methodology and performance limits. At the time when the new version was written its effects on system compliance were unknown. Landauer provides individual monitoring services for ionizing radiation dosimetry worldwide. The service for neutrons is based on an internally developed dosemeter called Neutrak® which has two versions: Neutrak-J for fast neutrons and Neutrak-T for fast and thermal. The study described here focuses on the neutron dosimetry system as implemented at the Paris office. This system has been tested by the UK National Physical Laboratory (NPL) against ISO 21909–1:2015. The NPL is one of the few calibration laboratories able to cover the extensive series of tests required by the standard. The purpose of this paper is twofold. Firstly, it aims to present the differences between ISO 21909:2005 and ISO 21909–1:2015 for non-linearity, reproducibility, energy-angle dependency and fading. This illustrates the challenges arising from ISO 21909–1:2015 and should prove useful to other IMSs since, to the authors’ knowledge, the work described herein is the first of its kind. The second aim is to document the results of the type test of the LANDAUER neutron dose measurement process based on the Neutrak-T dosemeter.

Impact of new operational dosimetric quantities on individual monitoring services

The new operational dosimetric quantities framework, proposed in the ICRU95 report, has stimulated the scientific community to start investigations that aim to assess its impact on radiation protection practices. As part of this effort, the present study describes an inter-comparison exercise among individual monitoring services (IMSs) on passive whole-body dosimetry. The inter-comparison is performed in terms of both the existing operational dose quantity and its proposed replacement , to allow an evaluation of the actions that may be necessary to adapt dosimetry systems to the proposed quantity. For two of the tested IMSs, simple modifications to the detector response function, or the dose calculation algorithm, were sufficient to obtain results within acceptable limits. However, these approaches are not sufficient to give a level of performance comparable to that achieved in terms of . This may require a modification to dosemeter design.

UNCERTAINTY EVALUATION IN MEASUREMENT OF THE PERSONAL DOSE EQUIVALENT AT NINE INDIVIDUAL MONITORING SERVICES IN ASIA AND THE PACIFIC REGION

This paper presents the results of the evaluation of the uncertainty in measurement of the personal dose equivalent, Hp(10), at nine individual monitoring services (IMSs) in Asia and the Pacific region. Different types of passive dosemeters were type-tested according to the International Electrotechnical Commission 62387 requirements. The uncertainty in measurement was calculated using the Guide to the Expression of Uncertainty in Measurement approach. Expanded uncertainties ranged between 24 and 86% (average = 38%) for Hp(10) values around 1 mSv and between 14 and 40% (average = 27%) for doses around the annual dose limit, Hp(10) = 20 mSv. The expanded uncertainties were lower than the 1.5 factor in either direction proposed by the International Commission on Radiological Protection for doses near the relevant dose limits. This indicates an acceptable level of uncertainty for all participating IMSs. Uncertainty evaluation will help the IMSs to acknowledge the accuracy of their measurements.