1,721,316 research outputs found
Development and fabrication of microdosimeter arrays based on single-crystal diamond Schottky diodes
Full text linkThe interest in microdosimetry is growing thanks to the advancement in microdosimetric technologies, improving detector performance and reliability. Herein, the fabrication and characterization of a novel diamond-based microdosimeter are proposed. The microdosimeter consists of an array of single-crystal diamond Schottky diodes about 1.5 mu m thick connected in parallel. The detector prototypes are characterized using the ion beam-induced charge technique, employing a 6 MeV carbon ions microbeam. Despite a good overall response, the first prototypes are affected by the "bridge effect": a charge collection beneath the metallic bridges connecting the sensitive volumes (SVs), which alters the energy deposition spectrum. To mitigate the bridge effect, different technological solutions are explored: the selective growth of intrinsic diamond layers and the use of an insulating material such as photoresist. These second prototypes reveal a good SV spatial definition without any charge collection from the bridges and a good response homogeneity within the SVs ranging between 3% and 5% full-width-half-maximum among the different prototypes. While the cell-like thickness and lateral dimensions of SVs make the diamond microdosimeter array ideal for radiobiological applications, its array configuration can make it highly versatile to perform under different fluence rate conditions in particle therapy.Herein, a novel diamond array detector is reported for high spatial resolution microdosimetry. The novel technology succeeds in performing without any undesired charge collection from the metallic bridges connecting the sensitive volumes. To the authors' knowledge, this is the first time a diamond array detector achieves this result proving such sensitive volume definition
MICRODOSIMETRY OF CLINICAL ION BEAMS: CONVERTING SPECTRA FROM DIAMOND SLAB TO WATER OF DIFFERENT SHAPES
No full textMicrodosemeters are frequently used today to specify the radiation quality in the framework of ion-beam therapy. The heterogeneity of the detector shapes and the materials limits the possibility of comparing directly spectra and mean lineal energies. A method was recently studied to convert the spectra obtained with unidirectional ion beams in slab detectors to those obtained with detectors of different in shape and material. The method is based on the observation that the lineal-energy spectra of slab detector, in a restricted energy interval, approximate the Linear Energy Transfer distributions at corresponding material and particle type and energies. In this study, the experimental spectra collected with a slab diamond detector are converted to the spectra that would be obtained using water detectors of spherical and cylindrical shapes
Role of the film texturing on the response of particle detectors based on CVD diamond
No full textRecent improvements in the quality of diamond films grown by Chemical Vapour Deposition (CVD) have made synthetic diamond a very attractive material for detection applications. In this paper, polycrystalline diamond films synthesised by microwave plasma enhanced CVD using a CH4-CO2 gas mixture, previously investigated as particle detectors, have been characterised by X-ray diffraction and Raman spectroscopy. The detector response was measured in vacuo under irradiation with 5.5 MeV α-particle from a 241Am source. A systematic study of the influence of the film structural properties on the detector performance has been carried out by changing the methane concentration in the growth plasma and the deposition temperature. The existence of a correlation between growth conditions, film texturing and detector performance has been demonstrated. Independently of the substrate temperature, (100) orientated films exhibit the lowest detection efficiencies. The meas ured collection distances are smaller than the average grain sizes and seem to be limited by trapping centres within the grains. These results are confirmed by Raman analysis
Diamond based Schottky photodiode for radiation therapy In Vivo dosimetry
No full textDiamond has long been considered as a suitable material for the fabrication of radiation detectors due to its outstanding physical properties. Even more so in the specific case of radiation therapy dosimetry applications, where the near-tissue equivalence radiation absorption, good spatial resolution and radiation hardness are required. Recently, a synthetic single crystal diamond dosimeter was developed at “Tor Vergata” University in cooperation with PTW-Freiburg, showingexcellent dosimetric properties. Such a device was thus commercialized (microDiamond™, PTWtype 60019) and widely accepted by the medical physics community, due to its reproducibility, reliability, accuracy and versatility. In this work, a novel diamond based dosimeter for in vivoapplication developed in our laboratories is presented. A basic dosimetric characterization of detector performances was performed under irradiation with60Co and 6 MV photon beams. Response stability, short and long term reproducibility, fading effect, linearity with dose, dose rate dependence, and temperature dependence were investigated. The detector response was found to be reproducible and dose rate independent in the range between 0.5 and 5 Gy/min. Its temperature dependence was within 0.5% between 25 and 38 ◦C, and negligible fading effect was observed. The obtained results indicate the proposed novel diamond device as a promising candidate for in vivo dosimetry in radiation therapy application
Time resolved laser induced fluorescence for characterization of binders in contemporary artworks
No full textContemporary artworks are often realized with multi-component mixtures with unknown compositions, which may be subjected to an unforeseeable degradation. A detailed characterization of these materials provides relevant information both to plan proper restoration strategies and to prevent damages. In particular, binders identification represents one of the major problems in the conservation of the contemporary works of art. In this paper, five binders routinely employed in contemporary paintings, i.e. acrylic resins, ethylene vinyl acetate, dammar varnish and linseed oil, were studied by Time Resolved Laser Induced Fluorescence Spectroscopy (TR-LIF). Experimental results confirm the TR-LIF analysis capability to isolate specific contributions from the investigated constituents. The spectral features of ten commercial paints containing the above mentioned binders were analyzed as well. In this latter case, additional diagnostic techniques, such as X-Ray Fluorescence Spectroscopy and Fiber Optics Reflectance Spectroscopy, were demonstrated to provide useful complementary information to integrate TR-LIF resul
Evaluation of the dosimetric properties of a synthetic single crystal diamond detector in high energy clinical proton beams
No full textTowards a non-invasive approach for the characterization of Arabic/Christian manuscripts
No full textThe conservation and restoration of paper artworks play a fundamental role in the field of our Cultural Heritage. In this contest, the characterization of paper composition as well as degradation state is fundamental to determine the suitable restoration and conservation processes for paper artworks. In this work, we present an interdisciplinary study focalized on the not-invasive characterization of a group of 16 precious Arabic-Christian manuscripts (originating from different regions of the Arabian Peninsula used in Christian environment) of XIII century, collected in the Vatican Library (Biblioteca Apostolica Vaticana – BAV, Vatican City).
The aim of this study is focused onto the characterization of papers and inks compositions of these manuscripts, in order to understand if there are similarity between them, and in same way, to obtain information about the provenience of them. For this goal, several analytical techniques were applied by using portable instrumentation directly in the restoration laboratory of BAV, such as Infrared Reflectography, X-ray fluorescence and colorimetry. In addition, High Performance Liquid Chromatography with UV/VIS detection and Fourier Transform Infrared Spectroscopy were applied for the evaluation of the composition and the conservation status of these books by the analyses of the material, removed by a sampling method based on the sponges mainly used for cleaning of paper artworks.
Crossing the obtained results, we can characterize the composition of the paper and the inks, used in the various manuscripts. They present the same characteristics in terms of chemical composition, not linked on the region where the book was found, underlining that the used protocol for the paper and its production were the same in the Arabic Peninsula
Characterization of homoepitaxial diamond for ionizing radiation detectors
No full textSynthetic diamond has been proven as an important material for advanced electronic applications, such as those encountered in high energy physics and astrophysics. In fact, diamond transparency to visible light, its high carrier mobility, high breakdown field and strong resistance to chemical attack and radiation damage have suggested the potential application of this material for `solar-blind' UV detectors which have to operate in extreme environments. To avoid the possible problems connected with the presence of grain boundaries in polycrystalline diamond films, a great effort has been devoted to the optimization of the growth process leading to high-quality single-crystal diamond on diamond substrates (homoepitaxy). In this view, characterization studies play a crucial role, because they provide the feedback for the optimization of the deposition process, in order to obtain the best quality material. In this work, a characterization study of homoepitaxial diamond grown by chemical vapor deposition (CVD) on synthetic diamond substrates is presented. The samples have been deposited in a CVD tubular reactor using a CH<sub>4</sub>-H<sub>2</sub> gas mixture (1-7%) at approximately 560°C substrate temperature. The growth rate ranged between 0.9μm/h and 2.2μm/h, microwave powers between 520W and 720W. The crystalline quality of the diamond layer has been studied by means of Raman spectroscopy. Photoluminescence has been used to study the nature and the distribution of impurities, having energy levels in the diamond band gap, which influence negatively the electronic quality of the material. The results have been compared with electro-optical characterization of UV detectors for astrophysics based on the analyzed diamond samples. The growth parameters which guarantees both high material quality and optimal device response have been determined. [All rights reserved Elsevier
ΔE-E single crystal diamond based telescope
No full textAn innovative monolithic diamond based ΔE-E charged particle telescope was fabricated in a layered structure featuring an ultrathin ΔE stage coupled to an E stage, about 2μm and 500μm in thickness, respectively. The diamond telescope was characterized in coincidence mode using α-particles emitted by a 241Am source, whose energy can be reduced by traveling in air at different pressures. The experimental ΔE-E scatter plots were analyzed and compared with the results from the nuclear simulation program SRIM. A good agreement between the experimental and simulated data as well as a good detector performance were found in terms of energy resolution and charge collection efficiency. Our experimental results indicate that the developed ΔE-E diamond telescope prototype can be used to provide information about the type and the energy of particles in nuclear physics experiments. In addition, the micrometric size sensitive volume of the ΔE diamond detector of the proposed device is particularly promising for the microdosimetric characterization of hadron beams
Diamond detectors for dose and instantaneous dose-rate measurements for ultra-high dose-rate scanned helium ion beams
Full text linkBackground: The possible emergence of the FLASH effect—the sparing of normal tissue while maintaining tumor control—after irradiations at dose-rates exceeding several tens of Gy per second, has recently spurred a surge of studies attempting to characterize and rationalize the phenomenon. Investigating and reporting the dose and instantaneous dose-rate of ultra-high dose-rate (UHDR) particle radiotherapy beams is crucial for understanding and assessing the FLASH effect, towards pre-clinical application and quality assurance programs. Purpose: The purpose of the present work is to investigate a novel diamond-based detector system for dose and instantaneous dose-rate measurements in UHDR particle beams. Methods: Two types of diamond detectors, a microDiamond (PTW 60019) and a diamond detector prototype specifically designed for operation in UHDR beams (flashDiamond), and two different readout electronic chains, were investigated for absorbed dose and instantaneous dose-rate measurements. The detectors were irradiated with a helium beam of 145.7 MeV/u under conventional and UHDR delivery. Dose-rate delivery records by the monitoring ionization chamber and diamond detectors were studied for single spot irradiations. Dose linearity at 5 cm depth and in-depth dose response from 2 to 16 cm were investigated for both measurement chains and both detectors in a water tank. Measurements with cylindrical and plane-parallel ionization chambers as well as Monte-Carlo simulations were performed for comparisons. Results: Diamond detectors allowed for recording the temporal structure of the beam, in good agreement with the one obtained by the monitoring ionization chamber. A better time resolution of the order of few μs was observed as compared to the approximately 50 μs of the monitoring ionization chamber. Both diamonds detectors show an excellent linearity response in both delivery modalities. Dose values derived by integrating the measured instantaneous dose-rates are in very good agreement with the ones obtained by the standard electrometer readings. Bragg peak curves confirmed the consistency of the charge measurements by the two systems. Conclusions: The proposed novel dosimetric system allows for a detailed investigation of the temporal evolution of UHDR beams. As a result, reliable and accurate determinations of dose and instantaneous dose-rate are possible, both required for a comprehensive characterization of UHDR beams and relevant for FLASH effect assessment in clinical treatments
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