2240 IRRADIATED PERSONAL DOSEMETERS FOR THE IC2014 EURADOS INTERCOMPARISON AT SEIBERSDORF.

The Dosimetry Laboratory Seibersdorf was the irradiation laboratory for the IC2014 EURADOS intercomparison for individual monitoring. One hundred and twelve whole-body dosimetry systems with 30 dosemeters per dosimetry system participated in the intercomparison. In total, 2240 personal dosemeters were irradiated in photon reference radiation fields on the ISO water slab phantom in terms of personal dose equivalent Hp(10) and Hp(0.07). Two nuclide irradiation systems ((137)Cs and (60)Co gamma radiation) and a 320-kV X-ray radiation unit were used. The irradiation plan consisted of nine irradiation set-ups with five different ISO/IEC photon radiation qualities (S-Cs, S-Co, RQR 7, W-80 and W-150) and two different angles of radiation incidence (0° and 60°). Reference dose equivalent values were in the range of ∼1-500 mSv. Reference values were based on air kerma rate traceable to primary standard calibrations and appropriate conversion coefficients resulting in total expanded measurement uncertainties <6 %.

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.

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).

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.

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.

Shielding variation effects for 250 MeV protons on tissue targets.

This paper provides results of computer simulation studies with the goal to analyse issues regarding radiation protection for personnel, patients and third persons involved in hadron therapy treatment. The treatment room and the patient are modelled by simple cylindrical geometries at incident proton energies of 250 MeV. Monte Carlo simulations of the energy and angular dependence of proton, neutron and photon radiation fields and resulting ambient dose equivalent distributions outside the shielding walls are performed. In order to investigate systematic uncertainties due to the shielding materials and inherent to the computer models, various concrete compositions, densities and water contents are modelled, and the influence of simulation parameters on the results obtained is determined. Generally, good agreement is found between results provided by MCNPX and FLUKA computer codes. Variations in neutron ambient dose attenuation from -50 to +/-30% are found due to varying concrete composition. Changes in the water content of the concrete in the order of 8% may cause variations up to 20%.

The use of the Monte Carlo simulation technique for the design of an H*(10) dosemeter based on TLD-100.

The thermoluminescence (TL) detector material LiF:Mg,Ti (TLD-100) and appropriate filter materials were combined in order to design a passive dosemeter measuring the operational quantity ambient dose equivalent, H*(10), for monitoring low-dose external photon radiation fields. Using the Monte Carlo simulation technique, optimisations of energy dependent conversion coefficients from air kerma free-in-air compared to ICRU and ISO proposed values. h*K(10), were performed by varying dosemeter detector positioning. geometrical arrangements, and filter materials. Deviations smaller than 5% compared to h*K(10) between 30 keV and 2.5 MeV of primary photon energies were achieved by a dosemeter design consisting of a 15 microm Sn metal layer and a 5 mm PMMA layer surrounding the LiF detector. Subsequently performed free-air verification experiments carried out in well defined standard photon radiation fields showed an obviously TL-specific effect. An underestimation up to -15% of the modelled data at low photon energies was observed.