EURADOS education and training activities.

This paper provides a summary of the Education and Training (E&T) activities that have been developed and organised by the European Radiation Dosimetry Group (EURADOS) in recent years and in the case of Training Courses over the last decade. These E&T actions include short duration Training Courses on well-established topics organised within the activity of EURADOS Working Groups (WGs), or one-day events integrated in the EURADOS Annual Meeting (workshops, winter schools, the intercomparison participants' sessions and the learning network, among others). Moreover, EURADOS has recently established a Young Scientist Grant and a Young Scientist Award. The Grant supports young scientists by encouraging them to perform research projects at other laboratories of the EURADOS network. The Award is given in recognition of excellent work developed within the WGs' work programme. Additionally, EURADOS supports the dissemination of knowledge in radiation dosimetry by promoting and endorsing conferences such as the individual monitoring (IM) series, the neutron and ion dosimetry symposia (NEUDOS) and contributions to E&T sessions at specific events.

THE RESULTS OF THE EURADOS INTERCOMPARISON IC2014 FOR WHOLE-BODY DOSEMETERS IN PHOTON FIELDS.

The European Dosimetry Group (EURADOS) first started performing international intercomparisons for whole-body dosemeters for individual monitoring services in 1998. Since 2008, these whole-body intercomparisons have been performed on a regular basis. In this latest intercomparison (IC2014), 96 monitoring services from 35 countries (mostly European) participated with 112 dosimetry systems. Unlike in the previous intercomparisons, the whole registration, communication and data exchange process was handled by a new on-line platform. All dosemeter irradiations were carried out in the Seibersdorf accredited dosimetry laboratory. The irradiation plan consisted of nine irradiation setups with five different photon radiation qualities (S-Cs, S-Co, RQR7, W-80 and W-150) and two different angles of radiation incidence (0° and 60°). The paper describes and analyses the individual results for the personal dose equivalent quantities Hp(10) and if requested, Hp(0.07), for all participating systems and compares these results with the ISO 14146 'trumpet curve' performance criteria. The results show that 100 systems (89 % of all systems) do fulfil the general ISO 14146 performance criteria. This paper gives an overview on the performance of the participating individual monitoring services and the influence of the dosemeter type on the observed response values.

EURADOS PROGRAMME OF INTERCOMPARISONS FOR INDIVIDUAL MONITORING SERVICES: SEVEN YEARS OF DEVELOPMENT AND FUTURE PLANS.

In 2008 the European Radiation Dosimetry Group (EURADOS) started a new programme of intercomparisons for individual monitoring services (IMS). The aim was to provide the possibility to IMS in Europe to participate in dosimetry intercomparions with regular time intervals with all types of dosemeter systems that are used routinely to monitor workers for exposure to external radiation. A self-evaluation of the programme shows that, apart from a few problems encountered, the programme can be judged as fit for its purpose. The results of a questionnaire among the participants support this conclusion. The conclusions encourage EURADOS to continue this programme of self-sustained intercomparisons for IMS.

EURADOS strategic research agenda: vision for dosimetry of ionising radiation.

Since autumn 2012, the European Radiation Dosimetry Group (EURADOS) has been developing its Strategic Research Agenda (SRA), which is intended to contribute to the identification of future research needs in radiation dosimetry in Europe. The present article summarises-based on input from EURADOS Working Groups (WGs) and Voting Members-five visions in dosimetry and defines key issues in dosimetry research that are considered important for the next decades. The five visions include scientific developments required towards (a) updated fundamental dose concepts and quantities, (b) improved radiation risk estimates deduced from epidemiological cohorts, (c) efficient dose assessment for radiological emergencies, (d) integrated personalised dosimetry in medical applications and (e) improved radiation protection of workers and the public. The SRA of EURADOS will be used as a guideline for future activities of the EURADOS WGs. A detailed version of the SRA can be downloaded as a EURADOS report from the EURADOS website (www.eurados.org).

Removing spurious signals from glow curves using an optimal Wiener filter.

During readout, the signal of the TLD is occasionally polluted with spurious signals. These most often take the shape of a spike on the glow curve. Often these spikes are only a few milliseconds wide but can have a height that significantly influences the outcome of the dose evaluation. The detection of spikes relies generally on comparing the raw glow curve with a smoothed version of it. A spike is detected when the height of the glow curve exceeds that of the smoothed curve, using criteria based on the absolute and relative differences. The procedure proposed is based on smoothing by an optimal Wiener filter, which is, on its turn, based on Fourier analysis for which numerically very efficient methods are available. Apart from having easy to understand tuning parameters, an attractive bonus is that, with only little additional computational effort, estimates of the position of peak maxima are found from second and third derivatives: a useful feature for glow curve quality control.

Energy response of different types of RADOS personal dosemeters with MTS-N (LiF:Mg,Ti) and MCP-N (LiF:Mg,Cu,P) TL detectors.

The photon energy response of different RADOS (Mirion Technologies) personal dosemeters with MTS-N (LiF:Mg,Ti) and MCP-N (LiF:Mg,Cu,P) thermoluminescence (TL) detectors was investigated. Three types of badges were applied. The irradiation with reference photon radiation qualities N (the narrow spectrum series), and S-Cs and S-Co nuclide radiation qualities, specified in ISO 4037 [International Organization for Standardization (ISO). X and gamma reference radiations for calibrating dosemeters and doserate meters and for determining their response as a function of photon energy. ISO 4037. Part 1-4 (1999)], in the energy range of 16-1250 keV, were performed at the Dosimetry Laboratory Seibersdorf. The results demonstrated that a readout of a single MTS-N or MCP-N detector under the Al filter can be used to determine Hp(10) according to requirements of IEC 61066 [International Electrotechnical Commission (IEC). Thermoluminescence dosimetry systems for personal and environmental monitoring. International Standard IEC 61066 (2006)] for TL systems for personal dosimetry. The new RADOS badge with the experimental type of a holder (i.e. Cu/Al filters) is a very good tool for identifying the radiation quality (photon energy).

Uncertainty assessment of a two element LiF:Mg,Ti TL personal dosemeter using Monte-Carlo techniques.

This paper presents the results of an uncertainty assessment and a comparison study of dose algorithms for H(p)(10) and H(p)(0.07) used for evaluating a routine two-element thermoluminescent whole-body dosemeter. Due to the photon-energy response of the two different filtered LiF:Mg,Ti detector elements, the application of a dose algorithm is necessary to assess the relevant photon doses over the rated energy range with an acceptable energy dependence. A linear dose algorithm with two different sets of parameters was designed to assess the personal dose equivalent in the relevant quantity H(p)(10) and H(p)(0.07). Based on the experimental results from calibrations on the ISO water slab phantom, a detailed uncertainty analysis was performed by means of Monte-Carlo (MC) techniques and other analytical methods. The uncertainty contribution of the individual detector element signals was taken into special consideration. For this analysis, realistic energy and angular distributions were applied to calculate the dosemeter response. It is concluded that the MC method is an appropriate tool to perform uncertainty calculations. The possibility to assign arbitrary probability density functions to the input quantities, as well as to define a complex model function (dose algorithm) allows the simulation of irradiation conditions close to reality.

EURADOS self-sustained programme of intercomparisons for individual monitoring services.

Within EURADOS working group 2, a system for self-sustained intercomparisons for individual monitoring services for external radiation was developed. With the intercomparison results, the participants can show compliance within their quality management system, compare their results with those from other participants and develop plans for improvement of their system. The costs of the exercises are covered by the participants fees. In this programme, the first intercomparison exercise for whole-body dosemeters has been executed in 2008 with 62 participating dosimetry systems from participants across Europe. In general, film systems show the largest deviations, although the results of some participants indicate that it is possible to achieve results with a film system with similar quality as for thermoluminescence dosimetry (TLD) systems. A second intercomparison has been organised for extremity dosemeters in 2009. For 2010 it is planned to organise a second intercomparison for whole-body dosemeters.

Results of the EURADOS extremity dosemeter intercomparison 2009.

This paper presents the results of an intercomparison for extremity dosemeters organised by the European radiation dosimetry group in 2009. In total, 59 systems were tested during this exercise including ring, stall and wrist dosemeters. A total of 1652 dosemeters were irradiated in the selected fields of photons and beta radiation qualities on appropriate phantoms (ISO finger and pillar phantom) in the dose quantity H(p)(0.07). All irradiations were carried out in selected accredited reference dosemetry laboratories (Seibersdorf Laboratories, Austria and IRSN, France). The results show that, especially at low-energy beta radiations ((85)Kr) and for beta irradiations with large angles of incidence (60°), many tested systems show pronounced under responses. On the other hand, for photon irradiations down to energies of 16 keV most systems showed good results. A participants meeting was held at IM2010 with discussion on both general aspects of this intercomparison and specific problems.

Hp(0.07) photon irradiations at Seibersdorf for the EURADOS extremity dosemeter intercomparison 2009.

In August 2009, almost 1000 passive extremity dosemeters were irradiated at the Dosimetry Laboratory Seibersdorf as part of the EURADOS intercomparison IC2009. Forty-four European individual monitoring services participated, with a total of 59 dosimetry systems (46 finger ring, 4 finger tip and 9 wrist/ankle dosemeter systems). Additionally, finger-ring dosemeters from the Dosimetry Service Seibersdorf were irradiated in a non-competitive manner. Dosemeter irradiations on rod and pillar phantoms in four photon-radiation fields complying with the ISO standard 4037 were performed with personal dose equivalent values (H(p)(0.07)) ranging from 4 to 480 mSv. Traceability was established by using an air-kerma-calibrated monitor ionisation chamber together with the X-ray facility as well as a calibrated (137)Cs gamma radiation field with a collimated beam geometry. The ISO-tabulated conversion coefficients from air kerma free-in-air to H(p)(0.07) were applied, resulting in the main contribution to the expanded measurement uncertainties.

Simulated and measured Hp(10) response of the personal dosemeter Seibersdorf.

The Hp(10) energy response of the personal dosemeter Seibersdorf and its two different filtered LiF:Mg,Ti (TLD-100) thermoluminescence (TL) detectors are investigated. A close-to-reality simulation model of the personal dosemeter badge including the wrapped detector card was implemented with the MCNP Monte Carlo N-particle transport code. The comparison of measured and computationally calculated response using a semi-empirical TL efficiency function is carried out to provide information about the quality of the results of both methods, experiment and simulation. Similar to the experimental calibration conditions, the irradiation of dosemeters centred on the front surface of the International Organization for Standardization (ISO) water slab phantom is simulated using ISO-4037 reference photon radiation qualities with mean energies between 24 keV and 1.25 MeV and corresponding ISO conversion coefficients. The comparison of the simulated and measured relative Hp(10) energy responses resulted in good agreement within some percent except for the filtered TL element at lower photon energies.

Background correction of personal dose distributions by a novel unfolding algorithm.

The dosimetry service Seibersdorf monitors more than 20,000 persons with typical monitoring period of one month. The use of thermoluminescence (TL)-dosemeters during the last 30 years allows measurements of even low dose values (some 10 muSv) with sufficient uncertainty. Consideration of the natural background contribution or transport dose which needs to be subtracted from the measured dose requires special protocols which differ significantly from country to country. The chosen protocol has not only a strong influence on the individual dose values (especially for low doses) but changes significantly the whole dose distribution function, as well as the corresponding statistical describing parameters (mean doses, median values, etc.) of these distributions. On the basis of the measured (uncorrected) distribution function the attempt was made to extract both the background doses as well as the remaining occupationally caused dose contribution. For this approach the uncorrected dose values of all customers from several years were analysed and a superposition of two independent log-normal distributions was assumed. By means of a new unfolding algorithm both components were isolated and the corresponding parameters were calculated. The paper gives a detailed description of the procedure and summarises the resulting dose distributions.

The right choice: extremity dosemeter for different radiation fields.

Measurements of weakly penetrating radiation in personal dosimetry present problems in the design of suitable detectors and in the interpretation of their readings. For the measurement of the individual beta radiation dose, personal dosemeters for the fingers/tips are required. LiF:Mg,Cu,P is a promising thermoluminescent (TL) material which allows the production of thin detectors with sufficient sensitivity. Dosimetric properties of two different types of extremity dosemeters, designed to measure the personal dose equivalent Hp(0.07), have been compared: LiF:Mg,Ti (TLD100) and LiF:Mg,Cu,P (TLD700H). A type test for energy response for photon and beta radiation according to ISO 4037-3 and ISO-6980 was carried out and the results for both dosemeters were compared. Simultaneous measurements with both types of dosemeters were performed at workplaces, where radiopharmaceuticals containing different radioisotopes are prepared and applied. Practices in these fields are characterized by handling of high activities at very small distances between source and skin. The results from the comparison of the two-dosemeter types are presented and analysed with respect to different radiation fields. Experiments showed a satisfactory sensitivity for the thinner dosemeter (TLD 700H) for detecting beta radiation at protection levels and a good energy response.

Monte Carlo study of a 60Co calibration field of the Dosimetry Laboratory Seibersdorf.

The gamma radiation fields of the reference irradiation facility of the Dosimetry Laboratory Seibersdorf with collimated beam geometry are used for calibrating radiation protection dosemeters. A close-to-reality simulation model of the facility including the complex geometry of a 60Co source was set up using the Monte Carlo code MCNP. The goal of this study is to characterise the radionuclide gamma calibration field and resulting air-kerma distributions inside the measurement hall with a total of 20 m in length. For the whole range of source-detector-distances (SDD) along the central beam axis, simulated and measured relative air-kerma values are within +/-0.6%. Influences on the accuracy of the simulation results are investigated, including e.g., source mass density effects or detector volume dependencies. A constant scatter contribution from the lead ring-collimator of approximately 1% and an increasing scatter contribution from the concrete floor for distances above 7 m are identified, resulting in a total air-kerma scatter contribution below 5%, which is in accordance to the ISO 4037-1 recommendations.

Determination of LiF:Mg,Ti and LiF:Mg,Cu,P TL efficiency for X-rays and their application to Monte Carlo simulations of dosemeter response.

The simulation of response of a new passive area dosemeter for measuring ambient dose equivalent H*(10) for photons has been performed using the Monte Carlo code MCNP and experimentally determined responses of LiF:Mg,Ti and LiF:Mg,Cu,P thermoluminescent (TL) detectors for hard-filtered X-ray spectra from 20 to 300 keV and for 137Cs and 60Co gamma radiation. Relative TL efficiency for both types of detectors, determined in experiments with bare detectors and similar Monte Carlo simulations, compared favourably with prediction of microdosimetric models for proposed microdosimetric target sizes in the range of 20-40 nm. The concluding verification experiment showed small deviations between measured and simulated dosemeter energy response values in the range of a few percent.

Study of real time temperature profiles in routine TLD read out--influences of detector thickness and heating rate on glow curve shape.

This paper reports the results of a study using a commercial routine read out system with non-contact hot nitrogen heating and linear heating gas profiles. Glow curves of LiF:Mg,Ti as well as LiF:Mg,Cu,P were analysed for different linear heating rates beta from 1 to 30 degrees K s(-1). Different thermoluminescent detectors (TLDs) of different thicknesses (0.38-0.90 mm) were studied and compared. By means of the application of CGCD program considering kinetic parameters of the used TL-material the analysis of the peak temperature of the individual TL peaks lead to the approximation of the real heating profile T(chip)(t) in the TL chip. The real heating profile deviates strongly from linearity and can be characterised by the solution of a differential equation T(chip)(t) = F [T(gas)(t)]. The model of this equation is discussed in the paper. The difference between gas and chip temperatures are heating rate and chip thickness dependent and reach values of up to 100 degrees C (for thick detectors and fast heating rates). Especially for LiF:Cu,P, knowledge of the real chip temperature is essential, since read out shall be performed at the highest possible temperature, without destroying the dosimetric properties of the material. On the basis of this work, an optimisation of the readout parameters for LiF:Cu,P is possible.

Aspects of harmonisation of individual monitoring for external radiation in Europe: conclusions of a EURADOS action.

Following the publication of the EU Council Directive 96/29, EURADOS coordinated two working groups (WGs) for promoting the process of harmonisation on individual monitoring of occupationally exposed persons in Europe. An overview of the major findings of the second WG is presented. Information on the technical and quality standards and on the accreditation and approval procedures has been compiled. The catalogue of dosimetric services has been updated and extended. An overview of national regulations and standards for protection from radon and other natural sources in workplaces has been made, attempting to combine the results from individual monitoring for external, internal and workplace monitoring. A first status description of the active personal dosemeters, including legislative and technical information, and their implementation has been made. The importance of practical factors on the uncertainty in the dose measurement has been estimated. Even if a big progress has been made towards harmonisation, there is still work to be done.

Quality control and reliability of reported doses.

Results of performance tests verifying the dosimetric properties of dosimetric systems are published in various reports (e.g. IAEA and EURADOS). However, there is hardly any information in the open literature relating to the uncertainty in a dose measurement or in the annual dose, which is increased by failure of the evaluation or data management system, damage of the dosemeter itself or by the loss of dosemeter. In this article, an attempt is made to estimate the importance of the above-mentioned conditions. This is achieved by sending questionnaires to about 200 approved dosimetric services in Europe. In total 88 questionnaires were returned and analysed. In the questionnaires, the frequency of occurrence of the various error conditions were investigated. Participants were also asked to evaluate the impact of the error condition from a dosimetric point of view and what countermeasures are taken. The article summarises all responses and compares different sources of errors according to their impact on the uncertainty of the resulting dose and gives a comprehensive overview on quality control actions and reliability on reported doses from European dosimetric services.

An example of abnormal glow curves identification in personnel thermoluminescent dosimetry.

The personal Dosimetry Service Seibersdorf analyses monthly a large number of thermoluminescent dosimeters (TLD). The dosimeters consist of LiF chips, and the readout is carried out with an automated Harshaw 8800 reader system. In some cases, the luminescent glow curves of the routine analysis do not have the expected form as a result of external chemical contamination, hardware problems, poor heat transfer, etc. It is therefore necessary to investigate the reasons for the irregularity of these curves. An algorithm for the investigation of the routine curves was developed. It is based on the fact that the shape of an abnormal glow curve differs from the shape of a normal one. An interesting type of abnormal glow curves in the routine service was found. Some dosimeters of a certain client, a steel industry, exhibit glow curves with an atypical shape and very high signals. In those dosimeters, a possible chemical contamination in the form of a powder was discovered, which interferes with the dosimetric signal. A quantitative analysis of that powder was made by means of inductively coupled plasma emission spectroscopy (ICP-OES) after microwave dissolution. Elements like aluminium, barium, calcium and others were found. Such elements are used in different combinations as thermoluminescent materials.