150 research outputs found

    VUV-Vis optical characterization of Tetraphenyl-butadiene films on glass and specular reflector substrates from room to liquid Argon temperature

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    The use of efficient wavelength-shifters from the vacuum-ultraviolet to the photosensor's range of sensitivity is a key feature in detectors for Dark Matter search and neutrino physics based on liquid argon scintillation detection. Thin film of Tetraphenyl-butadiene (TPB) deposited onto the surface delimiting the active volume of the detector and/or onto the photosensor optical window is the most common solution in current and planned experiments. Detector design and response can be evaluated and correctly simulated only when the properties of the optical system in use (TPB film + substrate) are fully understood. Characterization of the optical system requires specific, sometimes sophisticated optical methodologies. In this paper the main features of TPB coatings on different, commonly used substrates is reported, as a result of two independent campaigns of measurements at the specialized optical metrology labs of ENEA and University of Tor Vergata. Measured features include TPB emission spectra with lineshape and relative intensity variation recorded as a function of the film thickness and for the first time down to LAr temperature, as well as optical reflectance and transmittance spectra of the TPB coated substrates in the wavelength range of the TPB emission

    Optical spectroscopy and microscopy of radiationinduced light-emitting point defects in lithium fluoride crystals and films

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    Broad-band light-emitting radiation-induced F₂ and F₃⁺ electronic point defects, stable and laser-active at room temperature in lithium fluoride crystals and films, find applications in dosimeters, tuneable color-center lasers, broad-band miniaturized light sources and in novel radiation imaging detectors. A brief review of their photoemission properties is presented, and their peculiarities at liquid nitrogen temperature are discussed. A few experimental results about optical spectroscopy and fluorescence microscopy of these radiation-induced point defects in LiF crystals and thin films are presented to obtain information about the coloration curves, the point defects formation efficiency, the effects of the photo-bleaching processes, and so on. The control of local formation, stabilization and transformation of radiation-induced light-emitting defect centers is crucial for the development of optical active micro-components and nanostructures. Some of the advantages of low temperature measurements for novel confocal laser scanning fluorescence microscopy techniques, widely used for the spatial mapping of these point defects thorough the optical reading of their visible photoluminescence, are highlighted

    High resolution and high efficiency coloration of lithium fluoride by soft X-rays irradiation

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    The efficient coloration of LiF material, in the form of bulk and films, by EUV and soft X-rays emitted by a laser-plasma source is demonstrated. The short penetration depth of soft-X-rays is exploited to obtain high spatial resolution luminescent patterns while the high dynamic range of proportionality between X-ray dose and coloration is exploited for using LiF as image detector in micro-radiography and soft X-ray microscopy applications

    Thermal neutron detection by means of Timepix3

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    Thermal neutron detection plays a crucial role in numerous scientific and technical applications such as nuclear reactor physics, particle accelerators, radiotherapy,materials analysis and space exploration. There are several challenges associated with the accurate identification and quantification of thermal neutrons. The present work proposes a detailed characterization of a Timepix3 (TPX3) detector equipped with a Lithium Fluoride (6LiF) converter in order to study its response to thermal neutrons that are identified through the 6Li(n,α)3H reaction. The TPX3-based test system has been installed at the HOTNES facility in ENEA and the analysis highlighted its excellent performance showing high effectiveness in the identification of neutrons through morphological analysis of tracks produced by alpha and triton particles, after accurate discrimination from the gamma background. With the use of Monte Carlo simulations, it has been demonstrated that the main contribution is due to tritons and its signal can be used effectively in the identification of thermal neutrons obtaining an efficiency of 0.9 % for 25 meV neutrons. This allows the TPX3 to have important applications as an environmental monitor for thermal neutrons. This monitoring system can be simply realized and is easy to manage because of its compact size and its digital acquisition that allows a real-time analysis

    Contact X-ray microscopy of living cells by using LiF crystal as imaging detector

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    In this paper, the use of lithium fluoride (LiF) as imaging radiation detector to analyse living cells by single-shot soft X-ray contact microscopy is presented. High resolved X-ray images on LiF of cyanobacterium Leptolyngbya VRUC135, two unicellular microalgae of the genus Chlamydomonas and mouse macrophage cells (line RAW 264.7) have been obtained utilizingX-ray radiation in the water window energy range from a laser plasma source. The used method is based on loading of the samples, the cell suspension, in a special holder where they are in close contactwith a LiF crystal solid-state Xray imaging detector. After exposure and sample removal, the images stored in LiF by the softX-ray contactmicroscopy technique are read by an optical microscope in fluorescence mode. The clear image of the mucilaginous sheath the structure of the filamentous Leptolyngbya and the visible nucleolus in the macrophage cells image, are noteworthiness results. The peculiarities of the used X-ray radiation and of the LiF imaging detector allow obtaining images in absorption contrast revealing the internal structures of the investigated samples at high spatial resolution. Moreover, thewidedynamicrangeof theLiF imaging detector contributes to obtain high-quality images. In particular, we demonstrate that this peculiar characteristic of LiF detector allows enhancing the contrast and reveal details even when they were obscured by a nonuniform stray light

    Lithium fluoride thin film detectors for low-energy proton beam diagnostics by photoluminescence of colour centres

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    Optically transparent LiF thin films thermally evaporated on glass and Si(100) substrates were used for advanced diagnostics of proton beams of energies from 1.4 to 7 MeV produced by a linear accelerator for protontheraphy under development at ENEA C.R. Frascati. The proton irradiation induces the formation of stable colour centres, among them the aggregate F2 and F3 + optically active defects. After exposure of LiF films grown on glass perpendicularly to the proton beams, their accumulated transversal spatial distributions were carefully measured by reading the latent two-dimensional (2-D) fluorescence images stored in the LiF thin layers by local formation of these broad-band visible light-emitting defects with an optical microscope under blue lamp excitation. Taking advantage from the low thickness of LiF thin films and from the linear behaviour of the integrated F2 and F3 + photoluminescence intensities up to the irradiation fluence of ~5x1015 p/cm2, placing a cleaved LiF film grown on Si substrate with the cutted edge perpendicular to the proton beam, the 2-D fluorescence image of the film surface could allow to obtain the depth profile of the energy released by protons, which mainly lose their energy at the end of the path
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