1,721,076 research outputs found
Optical spectroscopy and microscopy of radiation-induced light-emitting point defects in lithium fluoride crystals and films
No full textBroad-band light-emitting radiation-induced F2 and F3+ electronic point defects, which are stable and laser-active at room temperature in lithium fluoride crystals and films, are used in dosimeters, tuneable color-center lasers, broad-band miniaturized light sources and novel radiation imaging detectors. A brief review of their photoemission properties is presented, and their behavior at liquid nitrogen temperatures is discussed. Some experimental data from optical spectroscopy and fluorescence microscopy of these radiation-induced point defects in LiF crystals and thin films are used to obtain information about the coloration curves, the efficiency of point defect formation, the effects of photo-bleaching processes, etc. Control of the local formation, stabilization, and transformation of radiation-induced light-emitting defect centers is crucial for the development of optically active micro-components and nanostructures. Some of the advantages of low temperature measurements for novel confocal laser scanning fluorescence microscopy techniques, widely used for spatial mapping of these point defects through the optical reading of their visible photoluminescence, are highlighted. © 2012 American Institute of Physics
Optimization of the theoretical dose distribution in the “Spread out Bragg Peak” (SOBP) region in proton therapy by means of semi-analytical techniques
No full textProton therapy uses proton beams to destroy cancer cells. Since the energy deposition of protons peaks at the end of the trajectory (Bragg peak), healthy tissues close to the target are partially spared. In clinical practice, beams of different energies are composed to obtain a broadened peak (SOBP, Spread Out Bragg Peak) to treat the entire lesion region in a uniform manner. In the framework of the TOP-IMPLART project (linear accelerator for proton therapy under construction at ENEA-Frascati), we present a semi-analytical method that allows to optimize SOBP uniformity for two different energy-modulation techniques, passive and active
Ion beam induced luminescence analysis of defect evolution in lithium fluoride under proton irradiation
No full textIon beam induced luminescence (IBIL) spectra of pure LiF under irradiation by a 2 MeV proton beam were analyzed as a function of the dose in order to deepen the kinetic mechanisms underlying the formation of luminescent point defects. The intensity evolution with dose at several emission wavelengths has been studied within a wide spectral interval, from ultraviolet (UV) to near infrared (NIR), and their different change rates have been correlated to the electronic defect formation processes. The intensity at few selected wavelengths was analyzed with a multiple linear regression (MLR) method in order to demonstrate that a linear calibration curve can be obtained and that an on-line optical dose monitor for ion beams can be realized.Ion beam induced luminescence (IBIL) spectra of pure LiF under irradiation by a 2 MeV proton beam were analyzed as a function of the dose in order to deepen the kinetic mechanisms underlying the formation of luminescent point defects. The intensity evolution with dose at several emission wavelengths has been studied within a wide spectral interval, from ultraviolet (UV) to near infrared (NIR), and their different change rates have been correlated to the electronic defect formation processes. The intensity at few selected wavelengths was analyzed with a multiple linear regression (MLR) method in order to demonstrate that a linear calibration curve can be obtained and that an on-line optical dose monitor for ion beams can be realized
Versatile lithium fluoride thin-film solid-state detectors for nanoscale radiation imaging
Full text linkPoint defects in insulating materials are successfully used for radiation detectors. Among them, colour centres in lithium fluoride (LiF) are well known for application in dosimeters and in light-emitting devices and lasers. LiF
thin-film detectors for extreme ultraviolet radiation, soft and hard X-rays, based on photoluminescence from aggregate electronic defects, are currently under development for imaging application with laboratory radiation sources, e.g. laser-driven plasma sources and conventional X-ray tubes, as well as large-scale facilities, e.g. synchrotrons and free-electron lasers. Among the peculiarities of these detectors, noteworthy ones are the very high intrinsic spatial resolution ( 1 cm2) and the wide dynamic range. Moreover, they are insensitive to ambient light and no development process is needed. The latent images stored in the LiF thin layer can be read with fluorescence optical microscopy techniques.
These detectors prove to be highly versatile, as LiF is sensitive to almost any kind of radiation, including charged particles and neutrons, and can be grown in the form of polycrystalline thin films, whose photoluminescence response can be tailored trough the control of the growth conditions
LiF Crystal probed by Ion Beam Induced Luminescence (IBIL) Analysis in Order to Identify a Linear Relationship Between Peak Intensities and Ion Beam Dose
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Spectral analysis of visible photoluminescence from F2 and F3+ color centers in low-dose gamma-irradiated lithium fluoride crystals at increasing excitation power
No full textLithium fluoride crystals were gamma irradiated at three different clinical doses (5, 10 and 20 Gy) with the 60Co reference beam of the Italian National Institute of Ionizing Radiation Metrology. The irradiations created optically-active point defects in the crystal lattice, among which the aggregate F2 and F3+ color centers, whose visible photoluminescence spectra were subsequently measured for increasing power densities of a 445 nm laser excitation in stationary conditions. The careful analysis of the spectra best fits vs. the excitation laser power suggests the presence of an emission band spectrally overlapped with the F3+ one and ascribable to F3 (R2) defects. Finally, a suitable elaboration of the resulting data for the emission band of the F3+ centers allows estimating a parameter of the energy triplet state of these defects, whose value well agrees with the literature
Radiophotoluminescence of color centers in lithium fluoride for novel radiation detectors in proton-beam diagnostics and clinical dosimetry
No full textThe peculiar photoluminescence properties of radiation-induced electronic defects in lithium fluoride (LiF), known as color centers, are well known for applications in tunable lasers and photonic light-emitting microdevices operating at room temperature. In the last two decades they have been under exploitation in radiation imaging detectors and dosimeters based on the optical reading of the visible photoluminescence in LiF crystals and polycrystalline thin films. They were proposed for soft X-ray imaging at high spatial resolution and, more recently, their use has been successfully applied to advanced diagnostics of proton beams. After proton irradiation of LiF, the emission intensity of the radiation-induced point defects is proportional to the absorbed dose over several orders of magnitude, thus novel solid-state dosimeters with imaging capabilities can be envisaged, although dose values that are typical of clinical radiotherapy are still a challenge. In this brief review, the main experimental results and recent advances concerning radiophotoluminescence of color centers in optically transparent LiF crystals and polycrystalline thin films are presented and discussed in order to highlight the advantages, challenges and limits related to the feasibility of detectors for protontherapy applications
Visible radiophotoluminescence of colour centres in lithium fluoride: From lasers to versatile radiation sensors
Full text linkThe peculiar photoluminescence characteristics of radiation-induced colour centres in lithium fluoride (LiF), well known for applications in optically-pumped tuneable lasers and broad-band miniaturised light-emitting photonic devices operating at room-temperature, are under exploitation in passive imaging detectors and dosimeters based on visible radiophotoluminescence in LiF crystals and polycrystalline thin films. Their high intrinsic spatial resolution, wide dynamic range and large field of view, combined with easy handling, ambient-light operation and no development need, allow to successfully extend their use from X-ray imaging to proton-beam advanced diagnostics and dosimetry, even at those low dose values that are typical of hadrontherapy. After exposure, the latent images stored in LiF as local formations of F2 and F3+ aggregate defects are read with an optical fluorescence microscope under illumination in the blue spectral range. Their visible emission intensity was found to be linearly proportional to the dose over at least three orders of magnitude, so that bi-dimensional LiF solid-state dosimeters based on spectrally-integrated radiophotoluminescence reading can be envisaged. Taking advantage of the low thickness of LiF thin films, transversal proton beam dose mapping was demonstrated at low proton energies, even at high doses. Recent results and advances concerning LiF crystals and polycrystalline thin film characterisation in the linearity range are presented and discussed with the aim of highlighting challenges related to increasing the LiF film detector radiation sensitivity to both particles (protons) and photons (X-rays), although therapeutic dose values typical of clinical radiotherapy are still a big challenge
Visualization by SNOM technique of optical modes in LiF channel waveguides
No full textElectron-beam lithography has been used to write optical waveguides at the surface of LiF. The ion implantation can be also used to produce planar and channel waveguides in LiF crystals by choosing appropriate implantation conditions. We report, for first time, on the visualization by SNOM of the modal structure of light propagation in channel waveguides directly formed in LiF crystals by both techniques
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