A method for evaluating personal dosemeters in workplace with neutron fields

Passive detectors, as albedo or track-etch, still dominate the field of neutron personal dosimetry, mainly due to their low-cost, high-reliability and elevated throughput. However, the recent appearance in the market of electronic personal dosemeters for neutrons presents a new option for personal dosimetry. In addition to passive detectors, electronic personal dosemeters necessitate correction factors, concerning their energy and angular response dependencies. This paper reports on the results of a method to evaluate personal dosemeters for workplace where neutrons are present. The approach here uses few instruments and does not necessitate a large mathematical workload. Qualitative information on the neutron energy spectrum is acquired using a simple spectrometer (Nprobe), reference values for H*(10) are derived from measurements with ambient detectors (Studsvik, Berthold and Harwell) and angular information is measured using personal dosemeters (electronic and bubbles dosemeters) disposed in different orientations on a slab phantom.     

Assessment of neutron dosemeters around standard sources and nuclear fissile objects

In order to evaluate the neutron doses around nuclear fissile objects, a comparative study has been made on several neutron dosemeters: bubble dosemeters, etched-track detectors (CR-39) and 3He-filled proportional counters used as dose-rate meters. The measurements were made on the ambient and the personal dose equivalents H*(10) and Hp(10). Results showed that several bubble dosemeters should have been used due to a low reproducibility in the measurements. A strong correlation with the neutron energy was also found, with about a 30% underestimation of Hp(10) for neutrons from the PuBe source, and about a 9% overestimation for neutrons from the 252Cf source. Measurements of the nuclear fissile objects were made using the CR-39 and the dose-rate meters. The CR-39 led to an underestimation of 30% with respect to the neutron dose-rate meter measurements. In addition, the MCNP calculation code was used in the different configurations.     

Use of composites of topaz-glass as TSEE and TL dosemeters

The properties of the thermally stimulated exoelectron emission (TSEE) and thermoluminescent (TL) emission of topaz-glass composites were studied with the aim of using them as solid-state dosemeters. The TSEE response was studied as a function of radiation energy and as a function of absorbed dose. Topaz-glass composites presented a linear TL and TSEE response to dose within a range of 0.01-1 Gy. The topaz-glass composites presented higher TSEE peaks than topaz-Teflon pellets. In the dosimetry of radiotherapic fields normally the responses of the topaz-glass dosemeters are comparable to topaz-Teflon pellets. The results confirmed that these new dosemeters can be useful in monitoring the quality of the radiation sources. This dose mapping technique is particularly useful in investigating dose distribution throughout a planned target volume.     

High-energy response of passive dosemeters in use at LANL

The high-energy neutron response of three passive dosemeters in use at the Los Alamos National Laboratory (LANL) has been investigated using metrology-grade fields. The dosemeters include the LANL Model 8823 TLD badge and the LANL PN3 track etch device. Both are dosemeters of record at LANL. The third device was the Personal Neutron Dosemeter (PND), a superheated emulsion device, manufactured by Bubble Technology Industries, Inc. (BTI). The response of the three dosemeters at neutron energies exceeding 10 MeV was assessed with monoenergetic neutrons at the Physikalisch-Technische Bundesanstalt facility (14.8 and 19 MeV). For the sake of completeness, data collected at lower energies are also included in this study. High-energy quasi-monoenergetic beams produced by the cyclotron facilities at the Université Catholique de Louvain (UCL) and the The Svedberg Laboratory (TSL) were also utilised as part of this study. These measurements were made to better understand and help interpret dosemeter readings obtained by workers at high-energy accelerators, such as the 800 MeV spallation neutron source facility located at the Los Alamos Neutron Science Center (LANSCE).     

Compliance of electronic personal neutron dosemeters with the new International Standard IEC 61526

The recommendations and test requests for the dose equivalent response of personal neutron dosemeters formulated by the new International Standard IEC 61526 are summarised. In particular, IEC 61526 allows the use of broad fields if dosemeters do not fulfil the hard requirements using monoenergetic neutrons. Some broad fields which can work as a replacement field using ISO sources ((252)Cf, (252)Cf (D(2)O mod.), (241)Am-Be) and simulated workplace fields (CANEL and SIGMA) are described. This work shows the results of recent measurements of the personal dose equivalent response for the dosemeters Thermo Electron EPD-N2, Aloka PDM-313 and the prototype dosemeter PTB DOS-2002, and discusses their compliance with respect to the new IEC 61526 standard.     

Angular dependence of the TL reading of thin alpha-Al2O3:C dosemeters exposed to different beta spectra

The angular dependence of the thermoluminescent (TL) signal of thin alpha-Al2O3:C dosemeters was investigated for a series of beta-emitting radionuclides commonly employed in nuclear medicine and characterised by different mean energies (99Tc, 177Lu, 90Sr/90Y and 90Y). Irradiations were performed in a controlled geometry, using a properly designed irradiator intended to realistically reproduce the situation of exposure of hospital personnel to beta-emitting pharmaceuticals. Under the conditions of extended source and short source to detector distance, the TL signal of thin alpha-Al2O3:C layers per unit irradiation time was observed to be independent on the angle of incidence within acceptable limits, particularly for those radionuclides with maximum energy >500 keV. This property may be easily explained by using simple physical considerations, such as the limited thickness of the dosemeters. The results confirm that these detectors are suitable for beta-ray extremity dose measurements, when the photon contribution is negligible, as in the case considered.     

The calibration of personal dosemeters used for evaluating exposure to solar UV in the workplace

In the framework of an epidemiological study regarding the correlation between solar UV radiation exposure and skin pathologies in a population of outdoor workers, the possibility of using polysulphone film personal dosemeters to quantify the Subjects UVB exposure has been evaluated. An original experimental set-up is presented. in a preliminary version, which ill be used both for solar irradiance spectroradiometric measurements and for the reading of personal dosemeters. The polysulphone absorption is similar to the CIE erythemal response curve. Due to UVB radiation exposure, the polysulphone film dosemeters photodegrade with a measrable absorbance change. The absorbance variation after the dosemeter exposure to UV radiation has been correlated to the UVB effective dose. The calibration curve obtained by this method may be particularly useful for the evaluation of small closes. The method will be used to quantify the personal exposure of workers whose exposure conditions are characterised by high variability.     

A catalogue of dosemeters and dosimetric services within Europe--an update

The catalogue of dosemeters and dosimetric services within the European Union (EU) Member States and Switzerland that was issued by EURADOS in the year 2000 has been updated and extended with information on dosimetric services in the new EU Member States and Bulgaria, Croatia, Romania, Serbia and Montenegro, and Ukraine. The total number of dosimetric services in these European countries is now estimated to be about 200. The present catalogue is based on information collected from 90 European dosimetric services, among which 34 questionnaires from 32 services were obtained over the years 2001-2004 for the first time. This article assesses and updates the present use of personal dosemeters and the extent to which occupationally exposed persons in Europe are monitored with dosemeters able to measure the operational quantity-personal dose equivalent, H(P)(d). The perspective of joining EU by the new countries accelerated the implementation of the EU Basic Safety Standard Directive to their national regulations. As a result, all newly investigated services reported their ability to measure H(P)(d). The catalogue provides information on the dosemeters, dose calculation and background subtraction algorithms, calibration methods, energy and angular response, and performance.     

New data on direct ion storage dosemeters

The DIS-1 dosemeter from the Finnish company RADOS is an innovative kind of passive electronic dosemeter for photon and beta radiation. This study examines the 'long-term' linear response behaviour, the calibration and readout accuracy with large samples of 'used' DIS-1 dosemeters especially in the low-dose region, which is of special interest for radiation protection issues. Our measurements prove the adequacy of the DIS-1 dosemeter for long-term-personal dosimetry. The fast and precise readout seems to make the DIS-1 dosemeter an ideal choice for personal dosimetry in low-dose environments.     

Performance testing of personal dosemeters from eleven dosimetry services in Sweden

The Swedish regulation, SSI FS 98:5, requires that radiological workers of category A use dosemeters from an approved personal dosimetry service. The 11 services operating in Sweden at the moment use five different types of dosemeter. All have been tested for their ability to determine Hp(10) and some of them to determine Hp(0.07) according to the European Commission report Radiation Protection 73, EUR 14852, of 1994. The five unique systems have been tested regarding the angular and energy dependence of the response of the dosemeters. The test points for the determination of Hp(10) are all, except one, within the trumpet curve and for the unique systems it is shown that the uncertainty related to angular response at three different energies is within the required +/- 40% except for the lowest X ray quality 40 kV. The energy dependence dominates over the directional dependence and the choice of radiation quality for calibration is of great importance for the system performance.     

Response of alanine and radio-photo-luminescence dosemeters to mixed high-energy radiation fields

Alanine and Radio-Photo-Luminescence (RPL) dosemeters are passive dosemeters used to monitor absorbed dose in all kind of radiation fields. However, up to now both dosemeter types are calibrated to photon sources only. In order to study the response of RPL and alanine dosemeters to mixed high-energy particle fields like those occurring at CERN's accelerators, an irradiation campaign at the CERN-EC High-Energy Reference field Facility (CERF-field) was performed. In this facility a copper target is irradiated by hadrons with a momentum of 120 GeV/c. Dosemeters were exposed to various mixed radiation fields by placing them at various positions on the surface of the target. In addition to the experiment FLUKA Monte Carlo simulations were carried out, which provide information concerning the energy deposition at the dosemeter locations. This paper compares the measurements with the simulation results and discusses the radiation field compositions present at the various dosemeter positions on the target.     

The outlook for the application of electronic dosemeters as legal dosimetry

This study analyses new trends of a set of 12 electronic personal dosemeters in order to gain an overview of their main advantages and limitations. Physical characteristics and radiological, mechanical and environmental performance were tested according to IEC-61526 Standard requirements. The study highlights the different behaviour of the selected dosemeters. In particular, it is demonstrated that three of the tested devices fulfilled most of the established requirements, whereas another three of them presented important faults. The parameters that need more development are, in general, the response at low energy photon and beta radiation, and the dose rate alarm features. In some cases, mechanical problems as well as interference in the response due to external electromagnetic fields were also found. However, the results of the study foresee a promising future for the application of the newest personal electronic dosemeters as legal personal dosemeters and show the need for internationally agreed technical requirements within the European countries.     

Using operational equipment to read accident dosemeters

Analysis of accident dosemeters usually involves the use of laboratory-based counting equipment. Gamma spectrometers are used for indium, copper and gold, and alpha-beta detectors for sulphur. This equipment is usually not easily transported due to the shielding required and the weight and delicacy of the counters. For intercomparison studies that require reading the dosemeters on site, a transportable system is required unless the site operating the study can count samples for all the participants. In the case of an actual accident these systems would have a difficulty in counting a large number of accident dosemeters. In an accident, personnel are usually subdivided according to their level of exposure. Those exposed to higher doses are treated immediately. An alternate system should be made available to handle the dosemeters worn by those personnel are likely to receive lower doses. Improvements in portable operational equipment for gamma and beta monitoring allow their use as spectrometers. Such a system was used for the SILENE intercomparison conducted at IRSN Valduc on 12 June and 19, 2002, and the preliminary results compared well with the other participants.     

Comparison test of electronic dosemeters

To assist with a planned purchase of electronic dosemeters by the Swiss Federal Office for Civil Protection, the calibration laboratory of the Paul Scherrer Institute performed tests on 11 types of electronic dosemeters manufactured by 10 European and American companies. The technical specifications for the World Trade Organisation (WTO) tendering procedure were largely in accord with the specifications of the international standard IEC 61526. First tests were performed with samples from each type of dosemeter. The reproducibility of a dose of 0.1 mSv generated with 137Cs radiation at a dose rate of 2.1 mSv.h-1 was found adequate for all tested dosemeter types. The response for environmental levels of radiation showed a large variation, indicating insufficient background correction of some dosmeters. A very high dose rate of 10 Sv.h-1 provoked faulty dose readings for more than half of the tested dosemeters. Dosemeter response for low-energy photon radiation was satisfactory for two of the tested dosemeter types. Four dosemeter types were selected for extended technical tests. Three samples of each of these dosemeter types were purchased. For drop and temperature tests the specifications of the WTO tendering procedure outranged the specifications of the IEC standard. Whereas even at a temperature of -25 degrees C the tested dosemeters functioned normally, drops from a height of 2 m onto a wooden surface rendered the samples of two dosemeter types inoperative.     

Superheated emulsions as high-energy neutron dosemeters

Superheated emulsions being inexpensive, easy to fabricate, and having tissue equivalent composition make them as one of the popular neutron dosemeters. One more advantage is that they can be made insensitive to gamma rays by the choice of the sensitive liquid. It is observed that the response of commercially available bubble detector to neutron decreases above 20 MeV while its response is roughly flat in the 0.1-15 MeV region. This restricts its application as a dosemeter to high-energy neutrons. The response of bubble detector from Bubble Technology Industries, has been observed by using Pb-breeder for high-energy neutrons from different facilities in Japan. It is observed that 2-3 cm Pb-breeder is effective in increasing the response of the detector to the nominal value. Theoretical calculation using MCNPX code indicates an increase in neutrons in the energy range of 0.1-10 MeV with Pb-breeder. The present work indicates the possibility of using the bubble detector as a dosemeter to high-energy neutron using a Pb-breeder of proper thickness.     

Measured and calculated angular responses of panasonic UD-809 thermoluminescence dosemeters to neutrons

Multi-element thermoluminescence dosemeters (TLD), such as the Panasonic UD-809, are used in personal dosimetry. The Panasonic UD-809 dosemeter consists of one gamma sensitive and three neutron sensitive TLD elements with different filter materials. In this work, the neutron energy responses (the number of (n,alpha) reactions per neutron) of the neutron-sensitive TLD elements of the Panasonic UD-809 dosemeter were calculated using the MCNP Monte Carlo transport code. Experiments were performed in a calibration geometry with an unmoderated 252Cf neutron source. These measurements were made with the dosemeter placed on the centre front face of a polymethylmethacrylate (PMMA) slab phantom. The phantom was rotated in the horizontal plane from -90 to +90 degrees, in 15 degree increments. Good agreement between calculated and measured element responses was observed. The angular dependency of personal dose equivalent was also calculated for parallel beams of 252Cf neutrons and compared to the TLD element angular responses.     

Estimating effective dose for a cardiac catheterisation procedure with single or double personal dosemeters

In most countries of the European Union legislation requires individual determination and registration of the dose to radiological workers exposed to ionising radiation to check whether dose limits are exceeded. To assess stochastic risk, ideally effective dose (E) should be known. In practice, personal dose equivalent [H(P)(10)] is used as it can be measured with a personal dosemeter. The dosemeter reading may provide a reasonable assessment of H(P)(10), but it may deviate strongly from E, in particular in radiology procedures for medical diagnosis or intervention when protective clothing like lead-equivalent apron and thyroid collar is worn. In the literature various correction factors and algorithms to convert readings of single or dual dosemeters to an estimate of E can be found. An illustrative example of a cardiac catheterisation procedure, in which dose calculations are made by Monte Carlo simulation of radiation transport, shows that such corrections may still yield considerable overestimation.     

Evaluation of two personal dosemeters in polyenergetic mono- and multi-directional neutron fields

The neutron dose-equivalent response of two commercially available electronic personal neutron dosemeters was studied in several laboratory-produced broad-spectrum neutron fields. Fluence-weighted mean energies ranged from 200 keV to 4 MeV; personal dose-equivalent rates ranged from 75 to 10 mSv h(-1); and angles of incidence were multidirectional, 0 degrees, 30 degrees and 60 degrees. Three of these fields have been shown previously to resemble ones found in CANDU (Canadian Deuterium Uranium is a registered trademark of the Atomic Energy of Canada Limited) power plant workplaces. Both dosemeters were found to perform reasonably well across the range of energy spectra and angles of incidence. One type of dosemeter displayed values of the personal dose equivalent that were, at worst, within a factor of approximately 2 of the reference values and, at best, within a few per cent of the reference values. The other type displayed values of the personal dose equivalent that were consistently within unity and 20% of the reference values. Although the radiological performance of one was found to be more accurate, this device was also found to be the less rugged of the two. Some of the data acquired in this work were compared with results previously published by others. There was consistency between these sets of data.     

Dose measurement for medical staff with glass dosemeters and thermoluminescence dosemeters during 125I brachytherapy for prostate cancer

Photoluminescence glass dosemeters (PLDs) and thermoluminescence dosemeters (TLDs) are commonly used as a personal monitoring dosemeter. PLDs and TLDs were used for surface dose monitoring of medical staff involved in (125)I brachytherapy for prostate cancer because these dosemeters have a wide dose-response linearity and high sensitivity for low photon energy. Surface doses measured with PLDs agreed with those with TLDs within ～20 % except for a few cases. Surface doses at a surgeon's left hand and arm were higher than those at the other measuring points. A surgeon received a maximum dose of 650 μGy at the back of left hand. Surface doses to an assistant were <100 μGy. Surface doses to a nurse, a radiologist, an anaesthesiologist and a radiological technologist were <10 μGy. The occupational exposure to a surgeon could be reduced by the adjustment of fluoroscopic parameters and the use of lead gloves.     

Hp(0.07) photon dosemeters for eye lens dosimetry: calibration on a rod vs. a slab phantom

In recent years, several papers dealing with eye lens dosimetry have been published as epidemiological studies are implying that the induction of cataracts occurs even at eye lens doses of less than 500 mGy. For that reason, the necessity to monitor the eye lens may become more important than it was before. However, only few dosemeters for the appropriate quantity H(p)(3) are available. Partial-body dosemeters are usually designed to measure the quantity H(p)(0.07) calibrated on a rod phantom representing a finger while a slab phantom much better represents the head. Therefore, in this work it was investigated whether dosemeters designed for the quantity H(p)(0.07) calibrated on a rod phantom can also be worn on the head (close to the eyes) and still deliver correct results (H(p)(0.07) on a head). For that purpose, different types of partial-body dosemeters from routine use were irradiated at different photon energies on both a rod and a slab phantom. It turned out that their response values are within ±5% independent of the phantom if the quantity value for the respective phantom is used. Thus, partial-body dosemeters designed for the quantity H(p)(0.07) calibrated on a rod phantom may be worn on the head and used to monitor the eye lens dose due to photon radiation via the measurement of H(p)(0.07) on the head.