Quantification of the radiosensitization effect of high-Znanoparticles on photon irradiated cells: combining Monte Carlo simulations and an analytical approach to the local effect model.

In vitroexperiments show significant reduction in the survival fraction of cells under irradiation treatments assisted with high-Znanoparticles (NPs). In order to predict the radiosensitization effect of NPs, a modification of the local effect model (LEM), in which the energy deposition from NPs is assessed by Monte Carlo (MC) radiation transport codes, has been employed in the past. In this work, a combined framework that splits the consideration of the radiosensitization effect into two steps is proposed. The first step is the evaluation of the radial dose distribution (RDD) around a single NP ionized by a photon beam with given energy spectrum using MC simulation. Thereafter, an analytical approach based of the LEM and the calculated RDD is used for evaluation of the average dose and the average number of lethal lesions in a cell target due to a set of ionized NPs. The explicit expressions were derived for the case of a spherical cell target and the RDD describing by the power law function. RDDs around gold NPs (GNPs) of different radii were simulated using the MC technique and fitted by a power law function. The fitted RDD and the derived expressions were applied for calculation of the survival curves and relative biological effectiveness of a spherical MDA-MB-231 cell loaded with GNPs and irradiated with monoenergetic photons of 10-150 keV. The proposed framework provides a practical alternative to time-consuming MC simulations, enabling the assessment of the response of cell cultures to an irradiation treatment assisted with NPs for a wide variety of cell geometries, NP distributions and irradiation schemes.

Nanoscale dose deposition in cell structures under X-ray irradiation treatment assisted with nanoparticles: An analytical approach to the relative biological effectiveness.

In this study, an analytical model for the assessment of the modification of cell culture survival under ionizing radiation assisted with nanoparticles (NPs) is presented. The model starts from the radial dose deposition around a single NP, which is used to describe the dose deposition in a cell structure with embedded NPs and, in turn, to evaluate the number of lesions formed by ionizing radiation. The model is applied to the calculation of relative biological effectiveness values for cells exposed to 0.5mg/g of uniformly dispersed NPs with a radius of 10nm made of Fe, I, Gd, Hf, Pt and Au and irradiated with X-rays of energies 20keV higher than the element K-shell binding energy.

Thermoluminescence and optically stimulated luminescence properties of beta-irradiated TiO2:Yb nanoparticles.

The thermoluminescence (TL) and optically stimulated luminescenece (OSL) response of TiO2:Yb nanoparticles are studied. After beta irradiation, the materials developed a significant TL/OSL signal associated to several localized trapping states around 360-620 K. The OSL signal is mainly due to the releasing of trapped charges in the low temperature (360 and 460 K) trapping states. A computer glow curve deconvolution procedure was used to determine the activation energies and kinetic order of the TL processes.

Thermoluminescence properties of undoped and Dy3+ doped ZrO2 nanophosphor under beta-ray irradiation.

The thermoluminescence (TL) of undoped and Dy3+ doped ZrO2 nanocrystals under beta-ray irradiation is reported. The TL glow curves are the result of the overlapping of four TL peaks produced partly by the intrinsic defect of highly asymmetrical monoclinic structure and partly due to defects produced during the synthesis process. The introduction of dopant ions induces changes in the glow curve due to the enhancement of high temperature peaks intensity. The results show that both undoped and doped ZrO2 nanocrystalline phosphor present good TL efficiency as well as good dose response which qualify them as a potential beta-ray dosimeter.

Effect of Yb doping on the afterglow and thermoluminescent properties of ZnO nanophosphors.

ZnO nanophosphors prepared by a glycol mediated chemical synthesis exhibit afterglow (AG) and thermoluminescence (TL) after excitation with beta rays. These properties, which are of great interest in dose assessment of ionizing radiation fields, could be appreciably modified by Yb doping. Concentration of 1, 2 and 5% diminished the AG and TL efficiency and modified the TL glow curve shape significantly. However, the 5% Yb doping concentration reduced the AG and TL fading behavior, improving the use of ZnO:Yb (5%) as potential TL ionizing radiation dosimeter.

Dose dependences of radiation induced yield in mixed radiation fields.

A theoretical model that describes dose dependences of trap filling (radiation yield) in mixed radiation fields consisting of two components is proposed. The model consists of one type of electron traps and one type of hole traps and assumes as an initial step the creation of two types of tracks, each represented by some volume with a uniform electron-hole pair density, different for each track. The relaxation process that follows comprises interband recombination, trapping of electrons and holes, and recombination of electrons with trapped holes and of holes with trapped electrons. These processes result in filled traps in amounts depending on the absorbed dose in the track and the number and types of tracks created in a given region of irradiated matter. The summation over the matter with areas of different degrees of overlapping (assuming poisson distribution of the created tracks), gives expressions for the dependences of trap filling as a function of doses for separated and simultaneous irradiation. It is shown that the key parameters determining the behaviour of the dose dependences are the ratios between the doses in the separated tracks and the average doses delivered on the irradiated matter by the separated components of the mixed field. If the ratios of the average dose to the track dose are low, the dose dependences will be linear. In the opposite limiting case the dose dependencies go to saturation. The linear and additive approximations of dose dependences in a mixed field are valid at low doses only.

Optical absorption and thermoluminescence in single NaCl:Cu crystals exposed to 60Co and UV light.

Optical absorption (OA) and thermally stimulated luminescence measurements were performed on NaCl:Cu+(0.04 and 0.08%) crystals blocks grown by the Czochralski technique. The NaCl:Cu+ crystals were exposed to gamma rays from a 60Co source (0.954-30 kGy) as well as UV radiation. The radiation-induced defects were mainly F, Cu- and Cu+ centres, with absorption bands located at 464, 256.7 and 236 nm, respectively. The absorption bands were found to be independent of the Cu impurity concentration. As the gamma-dose irradiation increased, the absorption band at 256.7 nm decreased while the band at 236.3 nm increased highly along with the 256.7 nm band. The F-centres produced at high gamma-radiation dose while thermally bleached showed an increase of the Cu+ OA bands with a simultaneous decrease of Cu- absorption band. The bleaching with F-light showed the participation of the F centre generated by gamma radiation on the ion valence changes of the doping impurity as well as on the TL phenomenon. The TL measurements in NaCl:Cu crystals with both impurity concentrations demonstrated that the Cu+ concentration has a strong influence on the intensity and shape of the glow peaks.

Optically stimulated luminescence dosimetry performance of natural Brazilian topaz exposed to beta radiation.

Optically stimulated luminescence (OSL) has become the technique of choice in many areas of dosimetry. Natural materials like topaz are available in large quantities in Brazil and other countries. They have been studied to investigate the possibility of use its thermoluminescence (TL) properties for dosimetric applications. In this work, we investigate the possibility of utilising the OSL properties of natural Brazilian topaz in dosimetry. Bulk topaz samples were exposed to doses up to 100 Gy of beta radiation and the integrated OSL as a function of the dose showed linear behaviour. The fading occurs in the first 20 min after irradiation but it is <6% of the integrated OSL measured shortly after exposure. We conclude that natural colourless topaz is a very suitable phosphor for OSL dosimetry.

Thermoluminescence response of new KCl(X)Br(1-X):EuCl3 sintered phosphors exposed to beta and gamma radiation.

Alkali halides crystals have been the subject of intense research for an understanding of their radiation-induced defects and luminescence properties. They exhibit noteworthy thermoluminescence (TL) properties when exposed to ionising radiation. Currently, these materials are grown employing expensive and rather complicated techniques. In this work, the results on the TL properties of new alkali halides phosphors fabricated by a simple and inexpensive procedure are presented. The samples were made by mixing KCl, KBr and EuCl3 salts, and compressing them at a pressure of 3.2 x 10(7) Pa during 3 min, followed by sintering at 700 degrees C during 24 h under air atmosphere. The dosimetric response of the samples showed an increase with radiation dose in the 1.5-20.0 Gy dose range for beta and gamma radiation. The TL glow curves in sintered samples presented significant differences in their peak structures compared with monocrystalline samples, indicating that the nature of the trapping states and the recombination mechanisms may be different.

Performance of CVD diamond as an optically and thermally stimulated luminescence dosemeter.

Diamond is a material with extreme physical properties. Its radiation hardness, chemical inertness and tissue equivalence qualify it as an ideal material for radiation dosimetry. In the present work, the optically stimulated luminescence (OSL) and thermoluminescence (TL) characteristics of a 10 microm thick CVD diamond (polycrystalline diamond films prepared by chemical vapor deposition) film were studied in order to test its performance as a beta radiation dosemeter. The TL response is composed of four main TL glow peaks; two of these are in the range of 150-200 degrees C and two additional peaks in the 250-400 degrees C temperature range. The integrated TL as a function of radiation dose is linear up to 100 Gy and increases with increasing dose exposure. The dose dependence of the integrated OSL exhibits a similar behavior. The observed OSL/TL behavior for the CVD diamond film clearly demonstrate its capability for applications in radiation dosimetry with special relevance in medical dosimetry owing to the diamond's intrinsic material properties.

Optical absorption, TL and IRSL of basic plagioclase megacrysts from the pinacate (Sonora, Mexico) quaternary alkalic volcanics.

The paper presents the first results of an investigation on optical absorption (OA), thermally and infrared stimulated luminescence (TL and IRSL) of the Pinacate plagioclase (labradorite). The OA spectra reveal two bands with maxima at 1.0 and 3.2 eV connected with absorption of the Fe3+ and Fe2+ and IR absorption at wavelengths longer than 2700 nm. The ultraviolet absorption varies exponentially with the photon energy following the 'vitreous' empirical Urbach rule indicating exponential distribution of localised states in the forbidden band. The natural TL is peaked at 700 K. Laboratory beta irradiation creates a very broad TL peak with maximum at 430 K. The change of the 430 K TL peak shape under the thermal cleaning procedure and dark storage after irradiation reveals a monotonous increasing of the activation energy that can be explained by the exponential distribution of traps. The IRSL response is weak and exhibits a typical decay behaviour.

Thermoluminescence behaviour of KCL(1-x)Br(x):Pb2+ exposed to gamma radiation.

The thermoluminescence (TL) behaviour of solid solutions of lead doped KCl(1-x)Br(x) (X = 0.02, 0.35, 0.50, 0.65, 0.85, 1) mixed crystals exposed to gamma radiation at different doses from 60Co is reported. The TL glow curves of KCl(1-x)Br(x):Pb2+ crystal exposed in the range of 0-140 Gy is strongly dependent on composition X. The maximum temperature of the main TL glow peak was found to shift towards lower temperatures as composition X increased and a significant enhancement of the TL efficiency in KCl(1-x)Br(x):Pb2+ was found for X = 0.50 which is attributed to an increase in the vacancy concentration of the mixed halides at middle composition. The participation of the F-centre in the TL phenomenon particularly related to the main TL glow peak observed in mixed samples was also confirmed.

Application of a thermoluminescence method for the detection of irradiated spices.

Food irradiation is extremely effective at reducing food-borne illness as well as losses caused by infestation and contamination. Despite the well-established regulations that permit irradiation to control pathogens in spices, there are no widespread methods to detect previously irradiated food. Therefore, it has become necessary to develop new detection and dose determination methods for food subjected previously to irradiation. The present work deals with the application of the thermoluminescence (TL) phenomenon to detect irradiated spices. The process is based upon the thermoluminescence properties exhibited by the polymineral content of the irradiated specimen. After separating the organic material, it is possible to extract some polymineral substances that are suitable for thermoluminescence analysis due to interaction of the spice to ionising radiation. The method was successfully applied to examine irradiated and non-irradiated paprika of Mexican origin. The spice was irradiated with gamma rays at doses of 5, 10 and 15 kGy. The separated thermoluminescent polymineral was found to be composed mainly of quartz and feldspar. The thermoluminescence glow curve of the irradiated specimen shows a wide band peaked 228, 268 and 336 degrees C, resembling closely the combined TL of quartz and feldspars. The method allows for the determination of the retrospective dose exposure.

Study of the phototransferred thermoluminescence in KCl:Eu2+ phosphors.

The phototransferred thermoluminescence (PITL) processes play an important role in the optical stimulated luminescence (OSL) and thermoluminescence (TL) dosimetric properties in KCl:Eu2+ crystals. In the present work, experimental evidence is presented about the participation of F and Fz centres in the associated recombination luminescence mechanisms involved with all three phenomena. An analysis of the TL glow curve of KCl:Eu2+ exposed to X ray ionising radiation shows three main thermoluminescence peaks around 370, 390 and 470 K. The 470 K highest intensity peak, considered the dosimetric peak due to its low fading and linear dose behaviour, is strongly correlated to the F and Fz centres. Through optical absorption spectra measurements of an optically bleached specimen, it was found that a minimum occurs at 560 nm, coinciding with the F centre band in KCl:Eu2+. Moreover, the diminishing of the integrated TL 470 K peak intensity is also seen to have a minimum at 560 nm (F centres); it also happens simultaneously with an increase of the integrated TL peak associated to the Fz band. This supports the close relation of the F and Fz centres in the PTTL process in KCl:Eu2+.

Ultraviolet thermoluminscent dosimetry using high temperature peaks in KCl:Eu2+ crystals.

The thermoluminescence (TL) characteristics of KCl:Eu2+ irradiated with solar and monochromatic ultraviolet (UV) light have been investigated. The glow curves exhibit at least five TL peaks between room temperature and 673 K. The low temperature peaks (<500 K) are very sensitive to the UV radiation, but their intensities practically do not depend on the duration of solar irradiation and are determined by the ratio between the creation rate by UV and the bleaching rate by visible light. The high temperature 650 K peak is not so sensitive, but it is more stable under optical bleaching and its intensity increases supralinearly as exposure time increases. The creation spectrum of the 650 K peak presents a broad band with a maximum at 230 nm that extends in the long wavelength range at least up to 360 nm. The results obtained are discussed in relation to the development of a UV dosemeter with wavelength sensitivity dependence close to the action spectra of UV-related biological effects.

Thermoluminescence in CVD diamond films: application to actinometric dosimetry.

Diamond is considered a tissue-equivalent material since its atomic number (Z =6) is close to the effective atomic number of biological tissue (Z =7.42). Such a situation makes it suitable for radiation detection purposes in medical applications. In the present work the analysis is reported of the thermoluminescence (TL) and dosimetric features of chemically vapour deposited (CVD) diamond film samples subjected to ultraviolet (UV) irradiation in the actinometric region. The TL glow curve shows peaks at 120, 220), 320 and 370 degrees C. The 120 and 370 degrees C peaks are too weak and the first one fades away in a few seconds after exposure. The overall room temperature fading shows a 50% TL decay 30 min after exposure. The 320 degrees C glow peak is considered to be the most adequate for dosimetric applications due to its low fading and linear TL behaviour as a function of UV dose in the 180-260 nm range. The TL excitation spectrum presents a broad band with at least two overlapped components around 205 and 220 nm. The results indicate that the TL behaviour of CVD diamond film can be a good alternative to the currently available dosemeter and detector in the actinometric region as well as in clinical and medical applications.

Thermoluminescence properties of KCl(1-X)KBrX:Pb2+ mixed crystals.

A study is presented of the thermoluminescence (TL) of phosphors based on potassium halides doped with divalent lead, such as KCl:Pb2+, KBr:Pb2+ and the crystalline series KCl(1-X)Br(X):Pb2+. The defects in the crystals generated by irradiation have been investigated as well as the trapping and room temperature recombination mechanisms. The samples were gamma irradiated to a dose of 10 kGy. The TL spectral response during the recombination stage was obtained through simultaneous measurements of temperature, emitted light intensity and emission wavelength by using an automated thermoluminescence system with optical fibre couplings and a diode array as a detection device. The TL emission is a broad band in the 350-600 nm range with a maximum strongly dependent upon the mixed composition.