Investigations of the kinetic energy parameters of irradiated (La)‐doped phosphate glass

The current study characterizes and analyzes glow curves obtained from phosphate glass doped with different concentrations of lanthanum. Kinetic parameters of the glow curves obtained from beta‐irradiated phosphate glass samples doped with lanthanum were determined using a newly designed deconvoluted software. The obtained results from the analyses indicated that the glow curves of the phosphate glass samples were composed of five overlapping peaks. The activation energies of the five electron traps were located between 0.622 and 1.133 eV. The obtained kinetic parameters were evaluated using the designed software and another two methods and all revealed good agreement. The first three traps displayed non‐first‐order behaviour, while the two deep traps obeyed nearly first‐order kinetics.     

Misclassification of ELF occupational exposure resulting from spatial variation of the magnetic field

The adequacy of a single hip- or chest-worn magnetic field dosimeter to reliably classify subjects with respect to their occupational ELF magnetic field exposure is investigated. Hip-worn dosimeters consistently underestimate both whole-body average exposure and head exposure, tentatively regarded here as two possible definitions of the “true” exposure measurement. The approximate resulting bias in the relative risk estimate in hypothetical case-control studies is evaluated. A chest-worn dosimeter is found to be generally superior to a hip-worn one in assessing exposure during the occupational tasks considered here. © 1993 Wiley-Liss. Inc.     

Radiation dose measurements in a dental orthopantogram unit using indigenously developed optically stimulated luminescence dosimeters

Dental orthopantogram (OPG)/cone beam computed tomography (CBCT) scanners are gaining popularity due to their 3D imaging with multiplanar view that provides clinical benefits over conventional dental radiography systems. Dental OPG/CBCT provides optimal visualization of adjacent overlaying anatomical structures that will be superpositioned in any single projection. The characteristics of indigenously developed optically stimulated luminescence dosimeters, namely, aluminium oxide doped with carbon (Al₂O₃:C), lithium magnesium phosphate doped with terbium and boron (LiMgPO₄:Tb,B) and lithium calcium aluminium fluoride doped with europium and yttrium (LiCaAlF₆:Eu,Y) were evaluated for their use in dental dosimetry. The dose?response of these dosimeters was studied at X‐ray energies 60 kV, 70 kV and 81 kV. Radiation doses were also measured using Gafchromic film for comparison. Radiation dose was measured at eight different locations of a polymethyl methacrylate (PMMA) head phantom including eyes. The optically stimulated luminescence (OSL) sensitivity of LiMgPO₄:Tb,B is about 1.5 times and LiCaAlF₆:Eu, is about 20 times higher than the sensitivity of Al₂O₃:C. It was found that measured radiation doses by the three optically stimulated luminescence dosimeters (OSLDs) and Gafchromic film in the occipital region (back side) of a PMMA phantom, were consistent but variations in dose at other locations were significantly higher. The three OSLDs used in this study were found to be suitable for radiation dose measurement in dental units.     

Thermoluminescence characterization of Ag‐doped Li2B4O7 single crystal materials

In this study, the thermoluminescence (TL) characteristics of Ag‐doped and undoped lithium tetraborate (Li₂B₄O₇, LTB) materials, grown using the Czochralski method, were reported. The TL properties of LTB:Ag, such as glow curve structure, dose response, fading and reproducibility, were investigated. The glow curve of the Li₂B₄O₇:Ag single crystal consists of four peaks located at approximately 75, 130, 190 and 275°C; in undoped LTB, the single crystal shows a broad glow curve with peaks at 65, 90, 125, 160 and 190°C using a heating rate of 5°C/s in the 50–350°C temperature region. The high temperature peak of Ag‐doped sample at 275°C has a nonlinear dose response within the range from 33 mGy to 9 Gy. There is a linear response in the range of 33–800 mGy; after which, a sublinear region appears up to 9 Gy for Ag‐doped LTB single crystal. For undoped single crystal, the dose response is supralinear for low doses and linear for the region between 1 and 9 Gy. The thermal fading ratio of the undoped material is almost 60% for the high temperature peak after 7 days. Ag‐doped LTB single crystal exhibits different behaviour over a period of 7 days.     

Thermoluminescent properties of some phosphor glasses based on aluminum oxide

The transparent thermoluminescent aluminum oxide‐based glass of 15Al₂O₃–35P₂O₅–25CaO–25Na₂CO₃, abbreviated as APCN (all in mol%) doped with different concentrations of SiO₂ from 0.0–500 ppm was prepared using a conventional melt‐quenching technique. The TL sensitivities of the prepared glasses were investigated at 3 Gy γ‐dose using a ⁶⁰Co source and measured at a heating rate 10 C/sec. The highest TL intensity of the material doped with SiO₂ was found at a concentration of 500 ppm (APCNSi₅). Deconvolution of the glow curve from APCNSi₅ resulted in four peaks at about 161, 194, 237 and 293 C with a Figure Of Merit (FOM) of 1.28%. The APCNSi₅ specimen had the best dosimetric properties when compared with the other samples. Reproducibility, repeatability, dose–response curve and fading effect were checked for peak 3, which appeared at about 237 C. The results displayed that the APCNSi₅ glass system was a low‐Z material (Z_eff ≈ 10), and had good reproducibility and good repeatability. Peak 3 showed good linearity over a dose range up to 20 Gy (R² = 0.999) and sublinearity behaviour was found. The signal from APCNSi₅ faded by about 11% after 2 days post irradiation, therefore it showed almost no significant loss. Such properties make the newly prepared glasses suitable for and highly recommended for use in γ‐dosimeters. Copyright © 2016 John Wiley & Sons, Ltd.     

Impact of transverse magnetic fields on dose response of a nanoDot OSLD in megavoltage photon beams

PurposeWe investigated the impact of transverse magnetic fields on the dose response of a nanoDot optically stimulated luminescence dosimetry (OSLD) in megavoltage photon beams.MethodsThe nanoDot OSLD response was calculated via Monte Carlo (MC) simulations. The responses R_Q and R_Q,B without and with the transverse magnetic fields of 0.35–3 T were analyzed as a function of depth at a 10 cm × 10 cm field for 4–18 MV photons in a solid water phantom. All responses were determined based on comparisons with the response under the reference conditions (depth of 10 cm and a 10 cm × 10 cm field) for 6 MV without the magnetic field. In addition, the influence of air-gaps on the nanoDot response in the magnetic field was estimated according to Burlin’s general cavity theory.ResultsThe R_Q as a function of depth for 4–18 MV ranged from 1.013 to 0.993, excepting the buildup region. The R_Q,B increased from 2.8% to 1.5% at 1.5 T and decreased from 3.0% to 1.1% at 3 T in comparison with R_Q as the photon energy increased. The depth dependence of R_Q,B was less than 1%, excepting the buildup region. The top air-gap and the bottom air- gap were responsible for the response reduction and the response increase, respectively.ConclusionsThe response R_Q,B varied depending on the magnetic field intensity, and the variation of R_Q,B reduced as the photon beam energy increased. The air-gaps affected the dose deposition in the magnetic fields.     

Dosimetric properties of lithium borate glass doped with dysprosium

Characterization of thermoluminescence (TL) properties of lithium borate glass samples doped with different concentrations of dysprosium (Dy) was carried out. Samples were prepared using a melting method at 1100°C and irradiated with β‐particles. The glass samples doped with 0.1% Dy displayed the best TL dosimetric properties compared with other compositions. Deconvoluted analyses of the glow curves displayed five overlapping TL glow peaks located between 392.0 and 510.3 K. A good linear TL dose–response for β‐particles was obtained in the dose range 66.6 mGy to 33.3 Gy. The minimum detectible dose was evaluated to be 205.4 μGy and samples revealed thermal fading in 312 h to 29% of their original value.     

Investigation of single-shot beam quality measurements using state of the art solid-state dosimeters for routine quality assurance applications in mammography

PurposeTo assess if single shot acquisitions with solid-state dosimeters as well as Robson’s method could replace ionization chambers for tube output and HVL measurements, saving medical physicists time.Material and methodsThe energy responses of 4 solid-state dosimeters with automatic calculation of HVL were compared to ionization chamber measurements. Five anode/filter combinations were tested: Mo/Mo, Mo/Rh, Rh/Rh, W/Rh and W/Ag, from 24kVp to 35kVp. Tube output was measured free in air. HVL was measured using the solid-state dosimeters (single-shot acquisition), then manually with aluminum sheets and finally using the parametrization method of Robson.ResultsDeviations in tube output and HVL related to energy response in SSD were small in the 25–32 kVp range, and for tube output typically within 3%. Extrapolation using the Robson parametrization was within 5%, except for one device and for all W/Rh. Deviations of the HVL using the single shot approach were within 10% of the gold standard data. Larger deviations were found at the extreme tube voltages of 24kVp and 35kVp (maximum of 24%).ConclusionWith the assumption that deviations in tube output of 5% and for HVL of 10% are acceptable, all tested solid state dosimeters met this criterion in the tube voltage range of 26kVp to 32kVp. Robson’s method worked well for the spectra for which the method was developed, making both alternative approaches trustworthy for routine quality assurance purposes.     

Is UV-B radiation affecting charophycean algae in shallow freshwater systems?

The objective of this study was to determine the effects of UV-B radiation on charophycean algae under natural conditions, since charophytes enhance water transparency in freshwater systems and levels of UV-B radiation have increased by ozone depletion. Potential and actual UV-B effects were studied by combining a glasshouse experiment in which plants were exposed to various levels of UV-B radiation and field measurements in two freshwater systems dominated by charophytes in the Netherlands. The glasshouse experiment showed that charophytes were sensitive to UV-B radiation. UV-B radiation negatively affected growth, while it increased levels of DNA damage in Chara aspera. Moreover, the charophytes did not seem to develop UV-B screens to protect against UV-B radiation since no increase in UV-B absorbing compounds was found. At field conditions, both spectroradiometrical measurements and DNA dosimeters showed that UV-B radiation was attenuated quickly in both freshwater systems, indicating that UV-B does not reach the submerged charophyte vegetation. However, specific conditions, like fluctuating water tables, may result in UV-B exposure to charophytes for certain periods annually.     

Patient dose levels for seven different radiographic examination types

This study was carried out as a part of a comprehensive project to establish a national diagnostic reference level (NDRL), for the first time, in Saudi Arabia. Seven of the most common X-ray examinations (10 projections) were included. This study consisted of 200 patients who were referred for X-ray examinations at King Khalid University Hospital (KKUH). The selected X-ray examinations were skull (PA), kub (AP and LAT), ankle (AP and LAT), foot (AP/OBL and LAT/OBL), hib (AP and LAT) and sinuses paranasal (AP). Mean patient information and exposure parameters for these seven radiographic examinations were recorded at KKUH. Some of these radiographic examinations were compared with their corresponding values at other national places [Security Forces Hospital (SFH); King Abdulaziz City for Science and Technology (KACST)] in Saudi Arabia. We found that the patient mean dose values recorded at KKUH were varied from those recorded at other national places. Wide variations in patient dose arising from a specific type of X-ray examination at different national places suggests that significant reductions in patient dose would be possible without affecting image quality. Furthermore, variations in patient dose may emerge from the examination technique, clinical condition, radiologist skill, tube current, tube potential and focus to film distance. The data of this study will be useful for the formulation of NDRLs, and it is also provides local diagnostic reference levels for some diagnostic X-ray examinations at KKUH and other national places in Saudi Arabia.