New fortuitous materials for luminescence dosimetry following radiological emergencies

The effective management of radiological emergencies where members of the public not carrying conventional dosimeter have been exposed to doses of ionising radiation requires individual dose estimates to support medical triage. Biological and physical methods have been developed to address this issue. New materials and techniques have been sought to reinforce preparedness for such emergencies. Alternative materials, such as clothing, shoes, paper, plastic items, nail polish or banknotes were investigated using thermoluminescence (TL) and optically stimulated luminescence (OSL). Most of the materials and fabric tested exhibited either no detectable response to dose using luminescence technique, or a weak response yielding detection limits above 2 Gy, with the exceptions of a blue polyester fabric responding to infra-red stimulated luminescence (IRSL) and some types of polymer-based fabric that were found to have luminescence favourable characteristics for short - term dosimetry and particularly those containing mineral fillers. The most promising were fabrics containing calcium carbonate fillers, where the TL response to β radiations was measured with a detection limit as low as 4 mGy, and a relatively low native signal in the region of interest (≤ 200 °C). The fading was found to be slower for samples stored at -15 °C compared with samples stored at ambient temperature. A blind test was carried out and confirmed the potential of bags containing calcium carbonate fillers to provide reliable dose estimate for radiological triage. Furthermore, the TL signal of calcium carbonate fillers contained in the fabric of bags offers several advantages for accident dosimetry compared with other methods, such as a rapid dose assessment, the low cost value of the material and availability, and the possibility to map radiological doses is the fabric covers sufficient surface

Integration of new biological and physical retrospective dosimetry methods into EU emergency response plans : joint RENEB and EURADOS inter-laboratory comparisons

Purpose: RENEB, 'Realising the European Network of Biodosimetry and Physical Retrospective Dosimetry,' is a network for research and emergency response mutual assistance in biodosimetry within the EU. Within this extremely active network, a number of new dosimetry methods have recently been proposed or developed. There is a requirement to test and/or validate these candidate techniques and inter-comparison exercises are a well-established method for such validation. Materials and methods: The authors present details of inter-comparisons of four such new methods: dicentric chromosome analysis including telomere and centromere staining; the gene expression assay carried out in whole blood; Raman spectroscopy on blood lymphocytes, and detection of radiation induced thermoluminescent signals in glass screens taken from mobile phones. Results: In general the results show good agreement between the laboratories and methods within the expected levels of uncertainty, and thus demonstrate that there is a lot of potential for each of the candidate techniques. Conclusions: Further work is required before the new methods can be included within the suite of reliable dosimetry methods for use by RENEB partners and others in routine and emergency response scenarios

Phototransferred TL properties of alumina substrates

Alumina substrates, such as those found as surface-mount resistors in mobile phones, are currently the strongest candidate as a surrogate dosimeter material in emergency radiological scenarios using luminescence techniques. However, the rate of fading of the luminescence signal (TL or OSL) imposes a limitation on their longer term use, and also increases the uncertainty in dose assessment. The potential of phototransferred thermoluminescence (PTTL) techniques to access deep traps in alumina substrate samples is reported here. A measurement procedure employing blue (470 nm) illumination was found to produce a PTTL signal with a detection limit of ca 100 mGy, but with a supralinear dose response below 10 Gy. By using a UV source with emission between 307 and 575 nm a linear dose response was obtained within this dose range, although the detection limit was higher (ca 200 mGy), partly arising from the presence of a non-radiation-induced photostimulated TL signal. Pulse annealing experiments indicate that deep traps providing a reservoir of charge are thermally accessible above 500 °C and require annealing to ca 700 °C to thermally clean them. Significantly, using blue illumination, storage experiments performed under dark conditions at room temperature indicate that the loss of charge in the deep traps accessed by the PTTL measurement procedure was less than 30% for storage periods of up to 224 days. Although the physical mechanisms associated with the transfer of charge from the deep traps probed by the PTTL measurements require further clarification, the possibility of significantly reducing the fading observed in conventional TL or OSL measurements introduces a potentially valuable tool in the use of this material for both short and long term dosimetry

Radiological emergency dosimetry – The use of luminescent mineral fillers in polymer-based fabrics

Mineral fillers are widely used in the manufacture of thermoplastics and they are commonly found in the fabrics used to form bags. We show that carbonate mineral filler grains incorporated within faux leather fabrics and the coatings applied to woven nylon fibre fabrics exhibit a bright thermoluminescence TL response to ionising radiation dose, similar to that of calcite, with a broad thermoluminescence (TL) peak at 100 °C. The fabrics tested are shown to be potentially suitable as a surrogate material for emergency dosimetry, exhibiting a linear TL response to dose between 0.1 and 10 Gy, and with a detection limit varying with fabric type from 4 to 400 mGy. The region of the TL glow curve selected for dose evaluation was between ca 100–200 °C, and this is restricted by the presence of a native signal associated with the 250 °C TL peak. The rate of fading observed varied with glow curve temperature, attributed to the presence of a distribution of trapping levels; following 24 h storage at room temperature the loss recorded for the optimal glow curve temperature region selected (160–162 °C) ranged from 30 to 80%, according to fabric and filler type. However, the fading mechanism is predominantly thermal and its rate can be substantially reduced by storing irradiated materials below room temperature. The use of filler minerals incorporated in the manufacture of plastics provides the scope to exploit a much wider range of materials for application to emergency dosimetry

Luminescence characteristics of some common polyester fabrics: Application to emergency dosimetry

A set of garment polyester-mix fabrics was tested for their potential suitability as surrogate dosimetry materials using optically and thermally stimulated luminescence techniques. A strong native blue-stimulated optically stimulated luminescence and thermoluminescence signal was observed with unirradiated samples, but this could be avoided by measurement of infra-red stimulated luminescence, and a sample of blue polyester-cotton mix fabric exhibited particularly high sensitivity to radiation dose. However, near complete fading at room temperature within several hours and rapid bleaching of the signal when exposed to daylight limit the deployment of this mode of measurement. The fading behaviour is critically dependent on the atmosphere in which the material is measured and on the storage conditions, where a reduction in oxygen significantly reduces the rate of fading. A cathodoluminescence study of the samples performed in a scanning electron microscope revealed complex emission spectra obtained with spatially integrated measurements and, in one fabric examined in more detail, the spatially resolved emission was found to vary in intensity and wavelength within the polyester fibre filaments which is likely to be associated with differences in crystallinity

Addressing Current Challenges in OSL Dosimetry Using MgB₄O₇:Ce,Li: State of the Art, Limitations and Avenues of Research

The objective of this work is to review and assess the potential of MgB4O7:Ce,Li to fill in the gaps where the need for a new material for optically stimulated luminescence (OSL) dosimetry has been identified. We offer a critical assessment of the operational properties of MgB4O7:Ce,Li for OSL dosimetry, as reviewed in the literature and complemented by measurements of thermoluminescence spectroscopy, sensitivity, thermal stability, lifetime of the luminescence emission, dose response at high doses (>1000 Gy), fading and bleachability. Overall, compared with Al2O3:C, for example, MgB4O7:Ce,Li shows a comparable OSL signal intensity following exposure to ionizing radiation, a higher saturation limit (ca 7000 Gy) and a shorter luminescence lifetime (31.5 ns). MgB4O7:Ce,Li is, however, not yet an optimum material for OSL dosimetry, as it exhibits anomalous fading and shallow traps. Further optimization is therefore needed, and possible avenues of investigation encompass gaining a better understanding of the roles of the synthesis route and dopants and of the nature of defects

Integration of new biological and physical retrospective dosimetry methods into EU emergency response plans – joint RENEB and EURADOS inter-laboratory comparisons

PURPOSE:RENEB, 'Realising the European Network of Biodosimetry and Physical Retrospective Dosimetry,' is a network for research and emergency response mutual assistance in biodosimetry within the EU. Within this extremely active network, a number of new dosimetry methods have recently been proposed or developed. There is a requirement to test and/or validate these candidate techniques and inter-comparison exercises are a well-established method for such validation.MATERIALS AND METHODS:The authors present details of inter-comparisons of four such new methods: dicentric chromosome analysis including telomere and centromere staining; the gene expression assay carried out in whole blood; Raman spectroscopy on blood lymphocytes, and detection of radiation-induced thermoluminescent signals in glass screens taken from mobile phones.RESULTS:In general the results show good agreement between the laboratories and methods within the expected levels of uncertainty, and thus demonstrate that there is a lot of potential for each of the candidate techniques.CONCLUSIONS:Further work is required before the new methods can be included within the suite of reliable dosimetry methods for use by RENEB partners and others in routine and emergency response scenarios