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21.
Thin films of polypropylene have been irradiated with different doses of gamma radiation from a 60Co source. IR, UV-VIS spectra of this polymer before and after irradiation have been recorded and from the spectral data some modifications in the properties have been investigated. The spectra indicated that polypropylene film was oxidised at the dose of 106 Gy. Due to the removal of additives, total destruction of the polymer takes place at this dose. Isotactic arrangement of the polymer is no longer present after irradiation. Growth of carbon cluster takes place above a gamma dose of 102 Gy. Thermal stability of the polymer changes due to irradiation and the polymer seems to decompose in four different steps at the highest dose of 106 Gy. 相似文献
22.
A kinetic model combining both localized and delocalized recombination is described which is based on different filling rates as a function of irradiation electron energy of a spatially correlated trapping center/luminescent center (TC/LC) complex. Following irradiation and thermal de-trapping the locally trapped electron-hole configuration is assumed to give rise to peak 5a and the e-only configuration to peak 5 in the glow curve of LiF:Mg,Ti (TLD-100). The model is capable of simulating the linear/supralinear dose response of composite peak 5, the dependence of the supralinearity on photon energy and the ratio of the intensities of peak 5a to peak 5 as a function of dose. However, this is achieved only by invoking the presence of band-tail states which allow thermally induced hopping leading to semi-localized recombination in the recombination mechanism of the e-only configuration. 相似文献
23.
Radiochromic film dosimetry is a promising technique, but at this time there are some artefacts, including non-uniformity, energy dependence and scanner artefacts. Accurate dosimetry with radiochromic films requires characterizing the film as well as the scanning and analysis procedures. In this work, the performance of the EBT3 films in combination with the EPSON Dual Lens Perfection V700 scanner for dose distribution measurements in stereotactic radiotherapy has been evaluated. It has been shown that it was necessary to perform 20 blank scans to obtain the stability of the scanner. In order to reduce the uncertainties due to the non-uniformity of the scan field, it was then decided to use the 12 × 12 cm2 central part of the scanner bed. Regarding EBT3 films, intra-sheet and inter-sheet uniformity of unexposed EBT3 films in terms of pixel value has been found to be respectively 0.27% (1 SD) and 0.15% (1 SD). No significant energy dependence has been observed above 30 keV and no angular dependence has been found. 相似文献
24.
Fiber optic radioluminescence dosimetry allows real-time dose rate measurements in complex, narrow geometries and at places of high dose rates, without exposing the operator or the susceptible electronics. The keys are the spatial separation of radiation sensitive probe and electronic processing system and their optical connection by a flexible light guide. The small probes are capable of measuring fields of high dose rate gradients and the sealed probe-tip qualifies for applications in the fluid milieu and even for in-vivo-dosimetry. One problem of fiber optic dosimetry is the generation of Cherenkov radiation and fiber luminescence in the irradiated light guide, the so called stem effect. Ruby (Al2O3:Cr) has a narrow radioluminescent emission at 694 nm and is a potential luminophor for fiber optic radioluminescence dosimetry. In this work the influence of the stem effect on our ruby-based fiber optic dosimetry system is examined. The behavior of ruby probes under irradiation up to 0.5 kGy, as well as their luminescence decay characteristics and the applicability for measurements in radiotherapeutic fields are investigated. 相似文献
25.
Small size (25 nm) Li2B4O7 nanoparticles doped with different concentrations of Cu, Ag and co-doped with Cu, Ag were prepared by solid state sintering at 700 °C. The crystalline phase and particle sizes analysis were carried out by XRD and TEM. FTIR study reveals the formation of vibrational bonds at 1600–1200 cm−1, 1500–700 cm−1, 950–870 cm−1 and 870–415 cm−1. The kinetic parameters of the TL glow curves were evaluated using CGCD procedure in R-software. The CW-OSL decay curves were fitted with third order exponential decay curves and photoionization cross sections of each component were evaluated. The lifetime of the main TL dosimetric peak were also calculated to check the stability of the signal. Dose responses of the synthesized Li2B4O7 nanoparticles for both the TL and CW-OSL were studied in the range of 0.02 mGy to50 Gy and found to be linear upto this range. Fading of the CW-OSL decay curves were also studied. The MDD of the synthesized samples were also calculated and observed to be 15 μGy. 相似文献
26.
J. Meissner M. Abs M. R. Cleland A. S. Herer Y. Jongen F. Kuntz A. Strasser 《Radiation Physics and Chemistry》2000,57(3-6):647-651
There is agreement in the scientific community that X-ray treatment of food at 7.5 MeV can be safe. Possible process improvements for treating at higher than 5 MeV X-rays have been re-visited. Monte Carlo methods have been applied to simulate the X-ray conversion process and to calculate dose distributions in homogeneous phantoms. Experimental data obtained using X-rays produced with a Rhodotron TT200 at 5 and 10 MeV verifies a representative set of data which is calculated with the presented method.
With this qualified Monte Carlo tool, calculations at 7.5 MeV incident electron energy were performed. The analysis gives special attention to higher photon yield, improved product penetration, as well as surface and edge effects. 相似文献
27.
A. Seeger 《辐射效应与固体损伤》2013,168(1-2):15-24
We have derived a simple empirical formula for sputtering yields of monatomic metals and semiconductors, taking the threshold effect for knock-on of atoms into account in the Sigmund theory. It is found that this semi-empirical formula fits to the energy dependence of the sputtering yields over a wide range of ion-target combinations. The best fit values of the parameters for the formula are given as a function of the ratio of the mass of target atoms and the mass of incident ions. 相似文献
28.
Erasure of the thermoluminescence (TL) signal on detector readout is considered to be a disadvantage of TL dosimetry, as post-readout dose reassessment is then impossible in principle. A method of dose reassessment based on phototransferred thermoluminescence (PTTL) has been developed at the Institute of Nuclear Physics, Polish Academy of Sciences (IFJ PAN) and applied to MTS-N (LiF:Mg,Ti) detectors. We demonstrate the possibility of applying PTTL for dose reassessment in MTS-N TL detectors routinely applied in the dosimetric service at IFJ PAN. Readings of TL detectors exposed to relatively high doses by the customers of our dosimetry service can now be reassessed using our automatic readers. A major obstacle in applying the PTTL method at lower exposures is the presence of residual dose accumulated in LiF:Mg,Ti detectors after many field exposure and readout cycles. Since most of the TL detectors in our service have been already used for a long time (e.g. for over 10 years in the case of some detector batches), we find that our PTTL method of dose reassessment is possible only in detectors which had received doses exceeding 5 mSv. 相似文献
29.
Gafchromic™ films have become popular due to their ease of use and their near water equivalence. This last property is crucial for stereotactic small beam dosimetry as demonstrated in recent papers. An accurate bi-dimensional dose measurement with Gafchromic™ films is very challenging mainly because of the non-uniformity response of flatbed scanners (used for films digitalization) and their own non-uniformity. The first proposal of this work is to develop bi-dimensional protocol for small beams and evaluate the associated uncertainty. The second proposal is to validate this protocol for the bi-dimensional measurements of treatment plans performed with the CyberKnife® system.First, the uniformity of an Epson V700 flatbed scanner and a batch of EBT3 Gafchromic™ films has been investigated. A “four films” dosimeter was designed to reduce the errors (statistic and systematic) due to their non-uniformity. Then, the “four films” dosimeter protocol in both a homogeneous (RW3 material) and heterogeneous (RW3, lung-like and bone-like materials) phantoms has been used to measure the bi-dimensional dose distributions of three simple CyberKnife® treatment plans. Two tumor locations (middle of the lung and near lung/bone interface) were considered for the heterogeneous phantom. These plans were achieved with the 10 mm fixed collimator and modeled with the PENELOPE Monte Carlo code in order to calculate accurate dose distributions. Finally, the “four films” bi-dimensional dose distributions were compared to the PENELOPE Monte Carlo simulations.Regarding the uncertainty associated to the bi-dimensional dose measurement protocol, the relative standard deviation σD on the dose was 1.2% in the range from 0.5 to 4.0 Gy. Regarding the protocol validation on CyberKnife® treatment plans, a very good agreement was found with all measurement points passing the {3% - 3 mm} Gamma Index criteria. 相似文献
30.