Area Dosemeters Research Articles

Response of current dosemeters to new operational quantities in rotational geometry.

Recently, the ICRU released Report 95, where new operational quantities for external radiation exposure are defined. The new quantities are defined in close relation to the protection quantities. This change affects the practice use of dosemeters. That is why the instruments must be adapted to the measurement of new quantities before their implementing as legally binding. The discrepancies depend on radiation spectra-particle type, energy of particles and direction of incidence. To analyse the performance of currently used instruments, irradiations in photon and neutron fields of various energies were performed for personal and area dosemeters. In this work, the response of photon and neutron personal dosemeters in conditions of rotational geometry is presented. The difference between the responses with respect to the new or old operational quantity was not large, which corresponded to the similar reference values for this irradiation geometry. The mutual ratio depended on the specific radiation quality and geometry. The behaviour of different types of dosemeters varied too.

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.

Low dose response results and detection limits of the EURADOS intercomparison IC2021area for passive H*(10) area dosemeters

The EURADOS intercomparison IC2021area with its main focus on low dose measurements was carried out between May 2021 and April 2022 for passive H*(10) area dosimetry systems. Three measurement conditions were provided at locations of the Karlsruhe Institute of Technology: 3-months indoor, 3-months outdoor and 6-months outdoor. The challenge for the 65 participating dosimetry systems of this intercomparison was measuring additionally irradiated low dose 137Cs gamma radiation of 150 μSv and 300 μSv. Despite the comparably high background dose values between about 200 μSv and 1600 μSv, more than 90% of the resulting response values of the irradiated dosemeters were within the recommended ISO 14146 response limits. The calculated detection limits of the participating dosimetry systems were in most cases clearly below the desired value of 150 μSv of this intercomparison.

TESTING DIFFERENT AREA DOSEMETERS CONCERNING THEIR BEHAVIOUR IN PULSED RADIATION FIELDS.

In Germany, authorised experts are required to measure around an X-ray facility to determine supervised and controlled areas within the scope of a legal regulatory procedure. For this purpose, they have to use area dosemeters which are nationally type-approved by the PTB according to the German measurement and verification act. To date, all available type-approved area dosemeters are only tested in continuous radiation fields, and therefore the technical data of the measuring instruments are valid only for continuous radiation. In practice, however, the majority of facilities use pulsed radiation X-rays. Since no other measuring equipment is available, the authorised experts use supposedly unsuitable dosemeters. But is this really so? In the scope of this article, instruments typically used for these measurements were tested to investigate their behaviour in pulsed radiation fields. The approach is similar to that of Friedrich et al.

EURAMET supplementary comparison of ambient dose equivalent H*(10) in 137Cs and ISO Narrow Beam Series N-60 x-ray beams at low dose rates

Comparison measurements among national standards laboratories are required to demonstrate their equivalence in the realization and transfer of the quantity ambient dose equivalent, H*(10), for photon radiation by these laboratories.The first comparison of the radiation protection quantity H*(10) with focus on the special needs for calibration of area dosemeters, low dose rates and large fields, started in January 2013 and was completed in December 2014. The comparison was piloted by the PTB as EURAMET project No. 1132 known also as EURAMET.RI(I)-S11.The operation and results of the comparison are reported here. The transfer instrument was a secondary standard ionization chamber for H*(10) with a volume of 10000 cm3. The response of this transfer instrument in various photon reference fields (N-60 and 1 mSv/h, S-Cs and 10 μSv/h, S-Cs and 1 mSv/h, radiation quality according to ISO 4037-1:1996 [1]) was compared.Measurements were made by the fourteen participants from the following countries: Germany, Austria, Greece, Norway, Sweden, Finland, Portugal, Spain, Czech Republic, Romania, the Netherlands, Slovenia, Italy and by one international organization. The results obtained by almost all of the participants are consistent with the stated uncertainties.KEY WORDS FOR SEARCHDosimetry, comparison, ambient dose equivalent, ISO narrow beam, EURAMET, CIPM MRA, BIPM KCDBMain textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

EURADOS intercomparison of passive H*(10) area dosemeters 2014

Under the umbrella of the European Radiation Dosimetry Group (EURADOS), different working groups have responded to the requests of monitoring services in Europe for independent tests of dosimetry systems for harmonization and quality assurance. After having performed regular intercomparisons of personal dosemeters, EURADOS Working Group 3, “Environmental Dosimetry”, performed the first EURADOS intercomparison for passive ambient dose equivalent, abbreviated H*(10), area dosemeters used for environmental monitoring in 2014 (IC2014env). Such dosimetry systems are generally used to monitor nuclear installations, besides other applications. The results of this intercomparison with a total of more than 500 dosemeters help to better understand influence parameters and the possible accuracy of typical dosimetric measurements using passive dosemeters.

Dose measurements in pulsed radiation fields with commercially available measuring components.

Dose measurements in pulsed radiation fields with dosemeters using the counting technique are known to be inappropriate. Therefore, there is a demand for a portable device able to measure the dose in pulsed radiation fields. As a detector, ionisation chambers seem to be a good alternative. In particular, using a secondary standard ionisation chamber in combination with a reliable charge-measuring system would be a good solution. The Physikalisch-Technische Bundesanstalt (PTB) uses secondary standard ionisation chambers in combination with PTB-made measuring electronics for dose measurements at its reference fields. However, for general use, this equipment is too complex. For measurements on-site, a mobile special electronic system [Hupe, O. and Ankerhold, U. Determination of ambient and personal dose equivalent for personnel and cargo security screening. Radiat. Prot. Dosim. 121: (4), 429-437 (2006)] has been used successfully. Still, for general use, there is a need for a much simpler but a just as good solution. A measuring instrument with very good energy dependence for H*(10) is the secondary standard ionisation chamber HS01. An easy-to-use and commercially available electrometer for measuring the generated charges is the UNIDOS by PTW Freiburg. Depending on the expected dose values, the ionisation chamber used can be selected. In addition, measurements have been performed by using commercially available area dosemeters, e.g. the Mini SmartION 2120S by Thermo Scientific, using an ionisation chamber and the Szintomat 6134 A/H by Automess, using a scintillation detector.

Correction factors for the ISO rod phantom, a cylinder phantom, and the ICRU sphere for reference beta radiation fields of the BSS 2

The International Organization for Standardization (ISO) requires in its standard ISO 6980 that beta reference radiation fields for radiation protection be calibrated in terms of absorbed dose to tissue at a depth of 0.07 mm in a slab phantom (30 cm x 30 cm x 15 cm). However, many beta dosemeters are ring dosemeters and are, therefore, irradiated on a rod phantom (1.9 cm in diameter and 30 cm long), or they are eye dosemeters possibly irradiated on a cylinder phantom (20 cm in diameter and 20 cm high), or area dosemeters irradiated free in air with the conventional quantity value (true value) being defined in a sphere (30 cm in diameter, made of ICRU tissue (International Commission on Radiation Units and Measurements)). Therefore, the correction factors for the conventional quantity value in the rod, the cylinder, and the sphere instead of the slab (all made of ICRU tissue) were calculated for the radiation fields of 147Pm, 85Kr, 90Sr/90Y, and, 106Ru/106Rh sources of the beta secondary standard BSS 2 developed at PTB. All correction factors were calculated for 0° up to 75° (in steps of 15°) radiation incidence. The results are ready for implementation in ISO 6980-3 and have recently been (partly) implemented in the software of the BSS 2.

Dosimetric specification of mixed neutron-photon fields at Czech interim stores for spent nuclear fuel

c The objective was to describe dosimetric characteristics of neutron and photon component of mixed fields at three dry interim stores for the spent nuclear fuel situated in territories of two Czech nuclear power plants. Mixed fields depend mainly on the residual thermal power of the loaded fuel, but they are also influenced by the type of CASTOR casks used in each store. To determine values of ambient dose equivalent rate due to neutrons and photons around CASTOR casks, common area dosemeters were employed. As the neutron component of these fields was dominant, neutron spectra were measured by means of the Bonner spheres spectrometer among a few groups of four casks and on their lids. The values of ambient dose equivalent rate derived from neutron spectra were compared with those obtained by area dosemeters. To give an idea about dosimetric situation at the stores, ranges of ambient dose equivalent rate measured around casks are presented together with ratios of this quantity for neutrons to photons.

PTB intercomparisons of passive H*(10) area dosemeters for environmental monitoring

For measuring the quantity ambient dose equivalent, H*(10), various passive photon and neutron dosemeters have been newly developed and are used in particular for the monitoring of nuclear facilities in the radiation field of the natural ambient radiation. Since 2005, the Physikalisch-Technische Bundesanstalt (PTB) has been performing intercomparisons to study fundamental properties and the long-term behaviour of area dosemeters under real environmental conditions, i.e. the accuracy of photon and neutron measurements performed in the complex natural radiation field. Measuring bodies from four European countries were the participants, including Germany. The goal was, on the one hand, quality assurance for existing passive dosemeters and measurement procedures and, on the other hand, the experimental investigation of whether the requirements of the appropriate standards and guidelines are met in practical use.

SU‐E‐I‐28: Assessment of Maximum Patient Skin Dose for Interventional Radiology Procedures: Method and Uncertainty Analysis

Purpose: To develop a method for the assessment of patient's maximum skin dose in interventional radiology procedures. Methods: In the framework of EURADOS WG12, a European measurement protocol was developed to determine fluoroscopy patient skin dose for interventional procedures. The method investigates the use of XR‐RV3 gafchromic films, punctual TLDs and TLD sheets to intercept the X‐ray beam and measure the maximum skin dose. Beside investigating the optimal detector positioning, the method also looks for the most appropriate reading equipments and process (post‐exposure time analysis, projection vs. transmission scanning, etc.), calibration conditions (backscattering conditions, beam qualities etc.) and fitting procedure (inversely proportional to dose vs. traditionally‐used polynomials) based on a careful uncertainty investigation, Finally, the different dosemters are compared to establish the most practical and efficient method for clinical practice. Results: XR‐RV3 films, being large area dosemeters, proved to reproduce with good accuracy the dose distribution over the patient skin. Nonetheless, significant dependence with beam energy and quality, reading and fitting process was observed, which introduces important uncertainties in maximum skin dose measurement. Meanwhile, TLDs enabled precise dose estimates with lower uncertainty values but point TLD detectors may implicate missing the maximum dose location on the patient skin. Thus, TLD sheets could represent the most adapted tool for the assessment of fluoroscopy‐induced skin doses. However, nowadays, these are used only in few laboratories and remain inaccessible in clinical practice. The given recommendation on calibration, reading, fitting and data analysis will help Medical Physicists to conduct accurate dose assessments and optimize the radiation protection of the patient. Conclusion: The developed protocol standardizes practices of patient skin dose estimates in interventional radiology. Based on these results, the assessment, at European level, of alerts for interventional procedures using real‐time Kerma‐Area Product and Cumulative Air Kerma as skin dose indicators will be carried out. Research funded in the framework of EURADOS WG12. No disclosures, no conflict of interest.

Calibration of PADC-based neutron area dosemeters in the neutron field produced in the treatment room of a medical LINAC

PADC-based nuclear track detectors have been widely used as convenient ambient dosemeters in many working places. However, due to the large energy dependence of their response in terms of ambient dose equivalent (H * (10)) and to the diversity of workplace fields in terms of energy distribution, the appro- priate calibration of these dosemeters is a delicate task. These are among the reasons why ISO has introduced the 12789 Series of Standards, where the simulated workplace neutron fields are introduced and their use to calibrate neutron dosemeters is recommended. This approach was applied in the present work to the UAB PADC-based nuclear track detectors. As a suitable workplace, the treatment room of a 15 MV Varian CLINAC DHX medical accelerator, located in the Ospedale S. Chiara (Pisa), was chosen. Here the neutron spectra in two points of tests (1.5 m and 2 m from the isocenter) were determined with the INFN-LNF Bonner Sphere Spectrometer equipped with Dysprosium activation foils (Dy-BSS), and the values of H *(10) were derived on this basis. The PADC dosemeters were exposed in these points. Their workplace specific H*(10) responses were determined and compared with those previously obtained in different simulated workplace or reference (ISO 8529) neutron fields.

Neutron measurements around a TN85-type storage cask with high-active waste

Abstract Several types of casks have been deposited in the German interim storage facility for spent fuel assemblies and vitrified high-active waste (HAW) at Gorleben since 1995, most of them of the CASTOR® type. In 2008 a delivery of 11 TN85-type casks arrived. They belong to the Transnuclear/Areva cask family and, compared to the flasks of the German (GNS) CASTOR® type, they differ in the neutron shielding design. Generally, radiation exposure of personnel during transportation and storage of casks containing spent fuel and vitrified waste is caused by mixed photon/neutron fields. Frequently, especially at casks for vitrified waste from reprocessing, neutrons are the major component of radiation exposure. Spectrometric and dosimetric investigations were made around a cask of the TN85-type. Neutron fluence spectra and reference values of the ambient dose equivalent H*(10) were measured by means of a Bonner sphere spectrometer (BSS) at several locations on the cask surface and in its environment. Moreover, commercial area dosemeters, LB6411 neutron monitors and conventional AD 6-type photon dosemeters were used. In addition, the responses of two electronic personal dosemeters for mixed fields (EPD-N2, DMC 2000GN) and a TLD albedo dosemeter were investigated. The neutron spectra obtained from the BSS are presented and compared with former measurements at CASTOR® type casks. The relative responses of the LB6411 survey meter and the individual dosemeters are discussed. The LB6411 monitor indicates H*(10) around the TN85 cask with tolerable measuring uncertainties. The personal dosemeters provide acceptable results for photons but overestimate the neutron dose considerably.

Neutron field characterisation of the OB26 CRNA irradiator in view of its use for calibration purposes

The main goal of the present work is to characterise the neutron field of an OB26 irradiation system acquired by the Nuclear Research Center of Algiers for radiation protection purposes. Extensive Monte-Carlo (MC) calculations and measurements using BF(3)- and (3)He-based neutron area dosemeters were performed to estimate the contribution, on the energy neutron spectrum, of each component present in the bunker facility of the Algerian Secondary Standard Dosimetry Laboratory (SSDL) where the irradiator has been installed. For this purpose, new irradiation configurations based on the (241)Am-Be source placed in the OB 26/2 biological shielding inside its environment have been investigated by MC simulations, and comparison with the ISO spectrum has been performed. During MC simulations, sensitivity analysis has been considered to estimate the effect of several physical parameters on the neutron fluence and dose equivalent rates. In addition, the contribution of the gamma dose equivalent rates to the total neutron dose equivalent rates was estimated for both selected source-detector distances (SDDs) 150 and 200 cm. Finally, a theoretical approach has been adopted, using MCNP5 fluence rates, to estimate the readings of the instruments taking into account their response functions. A low mean difference (12 %) between measured and predicted dose equivalent rates for two selected SDDs has been observed. Overall, the obtained MCNP5 results regarding the actual SSDL irradiation facility are particularly encouraging, but need to be supported by further experimental data.

Dosimetry at an interim storage for spent nuclear fuel

The Czech nuclear power plant Dukovany started its operation in 1985. All fuel spent from 1985 up to the end of 2005 is stored at a dry interim storage, which was designed for 60 CASTOR-440/84 casks. Each of these casks can accommodate 84 fuel assemblies from VVER 440 reactors. Neutron-photon mixed fields around the casks were characterized in terms of ambient dose equivalent measured by standard area dosemeters. Except this, neutron spectra were measured by means of a Bonner sphere spectrometer, and the measured spectra were used to derive the corresponding ambient dose equivalent due to neutrons.

ISO Recommended Reference Radiations for the Calibration and Proficiency Testing of Dosemeters and Dose Rate Meters used in Radiation Protection

One of the activities of the International Organization for Standardization (ISO) is the preparation and revision of standards specifying the requirements for photon, beta and neutron reference radiations to be used in radiation protection for the calibration of personal and area dosemeters and for contamination monitors. The reference radiations are also specified for determining the response of the instruments as a function of radiation energy and angle of incidence. Radionuclide sources, X ray facilities, reactors and accelerators are utilised as radiation sources to cover the wide range of radiation types and energies The standards are intended to be applied by primary and secondary standard dosimetry laboratories, but information contained in the standards is widely applicable. The standards specify, in addition, fundamental requirements for an adequate characterisation of reference radiations and describe calibration procedures. The latter include the specification of phantoms (trunk, arm/leg, finger) for the calibration and type testing of personal dosemeters in terms of the operational quantities proposed by the ICRU. Conversion coefficients are provided for all the reference radiations. The present paper gives background information about the concepts of the calibration procedures, the choice of the reference radiations, and their dosimetry. The main features of the standards are described and illustrated by examples.

Progress on Calibration Procedures with Realistic Neutron Spectra

In order to fulfil the ICRP Recommendations, as given in ICRP Publication 60, regarding the primary dose limits and the revised quality factors, substantial improvements to the characteristics of current dosimetric instruments are necessary. This statement is particularly true for neutron monitoring; neutron individual dosemeters suffer from an evident lack of accuracy and sensitivity. As to area dosemeters, the energy dependence of their response is far from being satisfactory over the whole energy range. Until more elaborate systems appear on the market, a step towards obtaining more reliable values of dose derived from current devices can be obtained by considering carefully the calibration conditions for dosemeters. This paper deals with the calibration procedures as defined or in preparation in the relevant ISO committees, in the frame of the so-called realistic neutron spectra, which replicate some of the neutron spectra encountered at workplaces. Taking into account the energy response of a particular dosimetric device, the influence of several energy distributions of the calibration field on the indication of the dosemeter to be tested are quantified and compared with the calibration factor calculated from monoenergetic references. The experimental part of the work at the IPSN/SDOS facility in the Cadarache research centre is expected to illustrate the contribution of the realistic neutron spectra to the problem of calibration of radiation protection instruments.

Progress on Calibration Procedures with Realistic Neutron Spectra

In order to fulfil the ICRP Recommendations, as given in ICRP Publication 60, regarding the primary dose limits and the revised quality factors, substantial improvements to the characteristics of current dosimetric instruments are necessary. This statement is particularly true for neutron monitoring; neutron individual dosemeters suffer from an evident lack of accuracy and sensitivity. As to area dosemeters, the energy dependence of their response is far from being satisfactory over the whole energy range. Until more elaborate systems appear on the market, a step towards obtaining more reliable values of dose derived from current devices can be obtained by considering carefully the calibration conditions for dosemeters. This paper deals with the calibration procedures as defined or in preparation in the relevant ISO committees, in the frame of the so-called realistic neutron spectra, which replicate some of the neutron spectra encountered at workplaces. Taking into account the energy response of a particular dosimetric device, the influence of several energy distributions of the calibration field on the indication of the dosemeter to be tested are quantified and compared with the calibration factor calculated from monoenergetic references. The experimental part of the work at the IPSN/SDOS facility in the Cadarache research centre is expected to illustrate the contribution of the realistic neutron spectra to the problem of calibration of radiation protection instruments.