Application of the LPE-Grown LuAG: Ce Film/YAG Crystal Composite Thermoluminescence Detector for Distinguishing the Components of the Mixed Radiation Field.

Single-crystalline films (SCFs) of the LuAG: Ce garnet grown using the liquid-phase epitaxy method onto YAG single-crystal (SC) substrates were investigated for possible applications as composite thermoluminescent (TL) detectors. Such detectors may help to register the different components of ionizing radiation fields with various penetration depths, e.g., heavy charged particles and gamma or beta rays. It was found that the TL signal of LuAG: Ce SCF sufficiently differs from that of the YAG substrate concerning both the temperature and wavelength of emissions. Furthermore, even by analyzing TL glow curves, it was possible to distinguish the difference between weakly and deeply penetrating types of radiation. Within a test involving the exposure of detectors with the mixed alpha/beta radiations, the doses of both components were determined with an accuracy of a few percent.

3D Dosimetry Based on LiMgPO4 OSL Silicone Foils: Facilitating the Verification of Eye-Ball Cancer Proton Radiotherapy.

A direct verification of the three-dimensional (3D) proton clinical treatment plan prepared for tumor in the eyeball, using the Eclipse Ocular Proton Planning system (by Varian Medical Systems), has been presented. To achieve this, a prototype of the innovative two-dimensional (2D) circular silicone foils, made of a polymer with the embedded optically stimulated luminescence (OSL) material in powder form (LiMgPO4), and a self-developed optical imaging system, consisting of an illuminating light source and a high-sensitive CCD camera has been applied. A specially designed lifelike eyeball phantom has been used, constructed from 40 flat sheet LMP-based silicone foils stacked and placed together behind a spherical phantom made by polystyrene, all to reflect the curvature of the real eyeball. Two-dimensional OSL signals were captured and further analyzed from each single silicone foil after irradiation using a dedicated patient collimator and a 58.8 MeV modulated proton beam. The reconstructed 3D proton depth dose distribution matches very well with the clinical treatment plan, allowing for the consideration of the new OSL system for further 3D dosimetry applications within the proton radiotherapy area.

Small is beautiful: low activity alpha and gamma sources for small-scale radiation protection research experiments.

PURPOSE: Uncertainties regarding the magnitude of health effects following exposure to low doses of ionizing radiation remain a matter of concern both for professionals and for the public. There is consensus within the international radiation research community that more research is required on biological effects of radiation doses below 100 mGy applied at low dose rates. Moreover, there is a demand for increasing education and training of future radiation researchers and regulators. Research, education and training is primarily carried out at universities but university-based radiation research is often hampered by limited access to radiation sources. The aim of the present report is to describe small and cost-effective low activity gamma and alpha sources that can easily be installed and used in university laboratories. METHODS AND RESULTS: A gamma radiation source was made from an euxenite-(Y) rock (Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6) that was found in an abandoned mine in Sweden. It allows exposing cells grown in culture dishes to radiation at a dose rate of 50 µGy/h and lower. Three alpha sources were custom-made and yield a dose rate of 1 mGy/h each. The construction, dosimetry and cellular effects of the sources are described. CONCLUSIONS: We hope that the report will stimulate research and training activities in the low dose field by facilitating access to radiation sources.

Intrinsic and Dopant-Related Luminescence of Undoped and Tb Plus Tm Double-Doped Lithium Magnesium Phosphate (LiMgPO4, LMP) Crystals.

In this work, the luminescence properties of undoped, Tm3+ doped, and Tb3+ plus Tm3+ double-doped crystals of the lithium magnesium phosphate (LiMgPO4, LMP) compound were investigated. The crystals under study were grown from melt using the micro-pulling-down method. The intrinsic and dopant-related luminescence of these crystals were studied using cathodo-, radio-, photo-, and thermoluminescence methods. Double doping with Tb3+ and Tm3+ ions was analyzed as these dopants are expected to exhibit an opposite trapping nature, namely to create the hole and electron-trapping sites, respectively. The spectra measured for the undoped samples revealed three prominent broad emission bands with maxima at around 3.50, 2.48, and 1.95 eV, which were associated with intrinsic structural defects within the studied compound. These were expected due to the anion vacancies forming F+-like centers while trapping the electrons. The spectra measured for Tb and Tm double-doped crystals showed characteristic peaks corresponding to the 4f-4f transitions of these dopants. A simplified model of a recombination mechanism was proposed to explain the temperature dependence of the measured thermally stimulated luminescence spectra. It seems that at low temperatures (below 300 °C), the charge carriers were released from 5D3-related Tb3+ trapping sites and recombination took place at Tm-related sites, giving rise to the characteristic emission of Tm3+ ions. At higher temperatures, above 300 °C, the electrons occupying the Tm3+-related trapping sites started to be released, and recombination took place at 5D4-related Tb3+ recombination centers, giving rise to the characteristic emission of Tb3+ ions. The model explains the temperature dependence observed for the luminescence emission from double-doped LiMgPO4 crystals and may be fully applicable for the consideration of emissions of other double-doped compounds.

Uniformity of Thermoluminescence and Optically Stimulated Luminescence Signals Over the Length of Doped LiMgPO4 Crystal Rods Grown by Micro-Pulling-Down Method.

The purpose of this work was to systematically assess the distribution of thermoluminescence (TL) and optically stimulated luminescence (OSL) properties along the length of crystals grown by the micro-pulling-down method, in relation to the microstructure and distribution of activators. We analyzed lithium magnesium phosphate (LiMgPO4; LMP) crystals doped with terbium (Tb; 0.8 mol%) or with a combination of thulium (Tm; 0.8 mol% or 1.2 mol%) and boron (B; 10 mol%). Crystals of several centimeters in length and 3 mm in diameter were cut into 20-40 slices, depending on length. For each sample, TL glow curves and OSL decay curves were examined. Optical microscopy and scanning electron microscopy were used to assess the microstructure and elemental composition of several selected samples. Two-dimensional TL readouts were performed to identify the areas with higher and lower signal emission. Our study showed that there may be significant differences not only in LMP sensitivity along the crystal's axis but also on the surface of the slice. The distribution of activators varies depending on the type of crystals and strongly affects luminescence properties.

Thermoluminescence Enhancement of LiMgPO4 Crystal Host by Tb3+ and Tm3+ Trivalent Rare-Earth Ions Co-doping.

We investigated the influence of terbium and thulium trivalent rare-earth (RE) ions co-doping on the luminescent properties enhancement of LiMgPO4 (LMP) crystal host. The studied crystals were grown from the melt by micro-pulling-down (MPD) technique. Luminescent properties of the obtained crystals were investigated by thermoluminescence (TL) method. The most favorable properties and the highest luminescence enhancement were measured for Tb and Tm double doped crystals. A similar luminescence level can be also obtained for Tm, B co-doped samples. In this case, however, the low-temperature TL components have a significant contribution. The measured luminescent spectra showed a typical emission of Tb3+ and Tm3+ ions of an opposite trapping nature, namely the holes and electron-trapping sites, respectively. The most prominent transitions of 5D4 → 7F3 (550 nm for Tb3+) and 1D2 → 3F4 (450 nm for Tm3+) were observed. It was also found that Tb3+ and Tm3+ emissions show temperature dependence in the case of double doped LMP crystal sample, which was not visible in the case of the samples doped with a single RE dopant. At a low temperature range (up to around 290 °C) Tm3+ emission was dominant. At higher temperatures, the electrons occupying Tm3+ sites started to be released giving rise to emissions from Tb-related recombination centers, and emissions from Tm3+ centers simultaneously decreased. At the highest temperatures, emission took place from Tb3+ recombination centers, but only from deeper 5D4 level-related traps which had not been emptied at a lower temperature range.

CALIBRATION OF LOW ENERGY X-RAY EXPERIMENTAL SETUP WITH STRONGLY FILTERED BEAM USING DATA FROM A SEMICONDUCTOR AND A THERMOLUMINESCENT DETECTORS.

The calibration of low energy X-ray experimental setup with strongly filtered beam dedicated to radiobiological research was performed using the absorbed dose calculated from the data collected by two types detectors. For this purpose a semiconductor (Amptek, USA) and a thermoluminescent (Institute of Nuclear Physics, Krakow, Poland) detectors were applied. The absorbed dose in water values estimated by both detectors are in good agreement.