[en] Monte Carlo modelling has been performed in support of efforts to establish emergency dosimetry services based on optically or thermally stimulated luminescence (OSL/TL) of the Al_2O_3 substrate present on the resistors found in mobile phones, which can act as fortuitous retrospective dosemeters for photon exposures. Specifically, a range of exposure conditions has been modelled to assess the dependence of the dosimetry on factors such as the position of resistors within a phone, the orientation of the phone relative to the source, and the location of the phone relative to its owner. Variations due to the resistors’ positions and the phone’s orientation were generally found to contribute just a few percent to the uncertainty on the dose assessments, though the electrical contacts surrounding the resistors could potentially enhance these by several 10s of percent. But, the location of the phone was found to impact dosimetry greatly. The largest discrepancies in the results were found for low-energy exposures: for "1"9"2Ir, differences of up to an order-of-magnitude were found between resistor and whole body doses. The outcome of the work was to derive correction / calibration factors that can be applied to estimate whole body doses from OSL/TL readings, the accurate application of which would depend on the knowledge of the exposure geometry and the degree of conservatism acceptable for the dose assessment. (paper)

[en] Uranium microparticles (radii: 50 nm-1.25 μm) were modelled surrounded by tissue and exposed to natural background radiation, in order to investigate potential dose enhancements from photon interactions. Generally, the results depended on the microparticle size. For a 0.5 μm radius microparticle in an isotropic field, it was found that the combined photon/electron doses deposited in 1 and 10 μm radii shells around it were raised by factors of ∼3.8 and ∼1.1, respectively; for a typical background photon fluence rate, these would correspond to increased energy depositions of a few 10's and a few 100's of eV y^-1, which are far less than the likely deposition rate resulting from the radioactive decay of a ²³⁸U microparticle. The health hazard from uranium microparticle interactions with background photons was concluded to be negligible. Published by Oxford Univ. Press on behalf of the Health Protection Agency 2010. (authors)

[en] The International Commission on Radiation Units and Measurements is considering revising the definitions of the operational dose quantities used for personal monitoring. This paper investigates the impacts of the proposed changes on the Public Health England two-element β/γ personal thermoluminescence dosemeter (TLD), in terms of its energy and angle dependences of responses for both skin and whole-body dose assessments. In general, the photon response of the skin element would be unaffected by the proposal, though technical issues may arise during calibration. For body photon doses, the current TLD design still produces acceptable response characteristics in some circumstances, but in general it will need to be redesigned to better match the requirements of the new operational quantity; to that end, a simple adaption is demonstrated that might provide a partial solution. For electron/beta exposures, matching the combined responses of both the body and skin elements to the dose quantities may be more challenging. The performance criteria against which dosemeters are judged may also need to be revised to reflect the proposed change. (paper)

[en] The ICRU is considering revising the definition of ambient dose equivalent. This paper investigates the impacts of the proposed change on four designs of neutron survey instrument, the GNU, HSREM, LB6411 and Studsvik 2202D, in terms of their respective energy dependences of response and their performances in realistic workplace fields. In some circumstances the current designs of instrument still produce acceptable characteristics, but in general they may need to be re-optimized to better match the requirements of the new operational quantity; to that end, a simple retrofit solution for the GNU is demonstrated. The performance criteria against which instruments are judged may also need to be revised to reflect the proposed change. (paper)

[en] The impact of depleted uranium (DU) on human health has been the subject of much conjecture. Both the chemical and radiological aspects of its behaviour in the human body have previously been investigated in detail, with the radiological impact being assumed to be linked to the alpha decay of uranium. More recently, it has been proposed that the accumulation in tissue of high-Z materials, such as DU, may give rise to enhanced local energy deposition in the presence of natural background photon radiation due to the high photoelectric interaction cross sections of high-Z atoms. It is speculated that, in addition to producing short-range photoelectrons, these events will be followed by intense Auger and Coster-Kronig electron emission, thereby causing levels of cell damage that are unaccounted for in conventional models of radiological risk. In this study, the physical and biological bases of these claims are investigated. The potential magnitudes of any effect are evaluated and discussed, and compared with the risks from other radiological or chemical hazards. Monte Carlo calculations are performed to estimate likely energy depositions due to the presence of uranium in human tissues in photon fields: whole body doses, organ doses in anthropomorphic phantoms and nano-/micro-dosimetric scenarios are each considered. The proposal is shown generally to be based on sound physics, but overall the impact on human health is expected to be negligible. (authors)

[en] In support of research aimed at developing a thermoluminescence dosemeter capable of accurately measuring ionising radiation doses to the lens of the eye, Monte Carlo modelling of a standard beta exposure set-up has been performed. It was found that electrons with an energy distribution corresponding to the beta emission spectrum from ⁸⁵Kr deposit negligible doses at a depth of 3 mm in tissue, but doses from ⁹⁰Sr/⁹⁰Y are significant; free in air and fluence-to-H_p(3,θdeg.) and -Hp(0.07,θdeg.) conversion coefficient data were found for this field for exposures at 0 deg., 30 deg. and 60 deg. angles of incidence, and the response characteristics of the new eye dosemeter were evaluated. It was shown that the results were not affected greatly by the shape of the calibration phantom. However, it was demonstrated that the presence of intermediating air and beam flattening filters hardens the energy distribution of the field at the point of test, relative to a raw ⁹⁰Sr/⁹⁰Y source, and this impacts dose depositions. (authors)

[en] A new head band dosemeter, for the measurement of eye lens dose in terms of H_p(3), has been type tested by Public Health England's Centre for Radiation, Environmental and Chemical Hazards [formerly part of the UK Health Protection Agency (HPA)]. The type tests were based on the International Standard ISO 12794, drawing also upon earlier work at HPA. The results show that, unlike many existing dosemeters, the new head band dosemeter correctly measures Hp(3) for beta radiations as well as photons. (authors)

[en] The Health Protection Agency is changing from using detectors made from ⁷LiF:Mg,Ti in its photon/electron personal dosemeters, to ⁷LiF:Mg,Cu,P. Specifically, the Harshaw TLD-700H card is to be adopted. As a consequence of this change, the dosemeter holder is also being modified not only to accommodate the shape of the new card, but also to optimize the photon and electron response characteristics of the device. This redesign process was achieved using MCNP-4C2 and the kerma approximation, electron range/energy tables with additional electron transport calculations, and experimental validation, with different potential filters compared; the optimum filter studied was a polytetrafluoroethylene disc of diameter 18 mm and thickness 4.3 mm. Calculated relative response characteristics at different angles of incidence and energies between 16 and 6174 keV are presented for this new dosemeter configuration and compared with measured type-test results. A new estimate for the energy-dependent relative light conversion efficiency appropriate to the ⁷LiF:Mg,Cu,P was also derived for determining the correct dosemeter response. (authors)