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Optically transparent lithium fluoride (LiF) thin films, thermally evaporated on Si(100) substrates, are under investigation as novel radiation detectors based on radiophotoluminescence for imaging of the full Bragg curves of proton beams produced by a linear accelerator for proton therapy under development at ENEA C.R. Frascati. Proton irradiation induces the formation of stable colour centres in LiF, amongst which the broadband light-emitting F2 and F3+ aggregate defects, whose concentrations are locally proportional to the energy deposited in the material. Their spatial distributions in the irradiated LiF thin films and crystals are carefully measured by acquiring the latent two-dimensional visible fluorescence images with an optical microscope under blue lamp excitation. Several LiF films grown on silicon substrate were irradiated in air at increasing proton energies up to 35 MeV with their surface parallel to the particle beam and a cleaved edge perpendicularly facing it; for each sample, the fluorescence image acquired from the top surface side of the film allows to obtain the depth profile of the energy released by protons. Differences in colour centre distributions detected in LiF films with respect to LiF crystals are presented and discussed. Accurate Monte Carlo simulations allow to fully explain their experimental behaviours, paving the way towards using LiF film radiation detectors on silicon for the advanced diagnostics of proton beams at typical particle energies used for proton therapy.

Solid-state radiation detectors based on the visible photoluminescence of radiation-induced F2 and F3+ color centers in lithium fluoride crystals have been used for advanced diagnostics of 18 and 27 MeV proton beams, produced by the TOP-IMPLART linear accelerator, which is under development for protontherapy applications at ENEA C.R. Frascati, Italy. Visible fluorescence microscopy was successfully used to read the latent proton beam images stored in the lithium fluoride crystals, thanks to high emission efficiency of the F2 and F3+ color centers obtained by simultaneous optical excitation in the blue spectral range. High intrinsic spatial resolution and wide dynamic range of these novel LiF detectors allow obtaining two-dimensional images of both the beam transverse intensity distribution and of the Bragg curve. By using a simple defect formation model that takes into account the energy released in the material and the saturation of defect concentration, not only the two-dimensional dose map was obtained from the beam transverse intensity distribution image, but also the full Bragg curve was reconstructed, allowing the thorough characterization of proton beams produced by the accelerator.

An analytical model that approximates Bragg curves due to protons in water is extended to lithium fluoride (LiF), both in bulk and lower-density homogeneous thin film form. To that purpose, Monte Carlo simulations of proton range for energies from 5 to 65 MeV are best fitted so that optimal values of the model parameters are deduced for LiF. Tests are performed by comparing analytically computed Bragg curves with corresponding ones simulated by Monte Carlo software in LiF, bulk and lower density, at two example proton energies and energy-straggling widths. The model is then applied to the reconstruction of the energy spectra of proton beams by best fitting experimental Bragg profiles due to visible photoluminescence of optically-active F2 and F 3 + color centers created in LiF crystals by the ionizing interaction of protons with the material.

Proton irradiation of lithium fluoride (LiF) crystals and thin films causes the formation of electronic defects, known as color centers, in the crystal lattice, some of which show photoluminescence in the visible range under blue-light excitation. With a suitable irradiation geometry, the energy density that protons deposit in the material can be recorded as a spatial distribution of these light-emitting color centers, from which a luminous replica of the proton Bragg curve can be thereafter extracted and analyzed in a fluorescence microscope. In this paper, the cases of two LiF thin films deposited on silicon substrates and of a LiF crystal, all of them transversally irradiated with a nominal 35 MeV proton beam, are considered. A comparison of the measured photoluminescent Bragg curves with Monte Carlo simulations demonstrates (i) that the Bragg peaks in the films are located at the very same positions that would be expected in the underlying silicon substrates rather than in LiF and (ii) that an even small grazing angle of the impinging proton beam is able to significantly modify the shape of the Bragg curve in the films. Both of these findings are ascribed to the effects of multiple Coulomb scattering in both the film and the substrate. The coincidence of the Bragg peak positions with those expected in the silicon substrates and the possibility of visualizing such peaks in the Bragg curves stored as latent fluorescence images in the LiF films allow one to regard them as information transducers for proton beam diagnostics and dosimetry.

Lithium 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.

Optical photoluminescence of thermally evaporated Alq3 thin films has been studied for over six years in a few samples annealed and non-annealed and afterwards exposed to the laboratory atmosphere. It was found that the measured emission intensity decays with four different time-spectral behaviors, which imply the existence of four molecular aggregations, or components. Insights have unveiled their interactions with environment agents, which are useful both for optoelectronic utilizations of this ubiquitous organo-metallic molecule possessing a long emission lifetime and for basic research and application of similar organic molecules.

Passive solid-state radiation detectors, based on the radiophotoluminescence of stable color centers in nominally pure lithium fluoride (LiF) crystals, have been used for advanced diagnostics of the segment up to 35 MeV of the TOP-IMPLART proton linear accelerator for protontherapy applications, under development at ENEA Frascati. In LiF, proton beams generate a spatial distribution of F2 and F3+ aggregate color centers, which efficiently emit radiophotoluminescence in the red-green spectral range under optical pumping around 450 nm. LiF crystals were irradiated with 35 MeV nominal energy protons at several doses of interest for protontherapy (from 0.5 to 50 Gy). For the first time is shown here the possibility of measuring the radiophotoluminescence spectra of proton irradiated LiF even at such low doses and how the signal showed a linear behavior with dose with a good signal-to-noise ratio. A Bragg-curve image, stored as color-center distribution in a LiF crystal after a 50 Gy-dose irradiation in a particular geometry, was acquired in a conventional fluorescence microscope. After appropriate image processing, the signal intensity resulted to be proportional to the linear energy transfer along the whole Bragg curve. By best-fitting it with an ad-hoc analytical formula, the depth-dose distribution was reconstructed and the proton beam energy and energy spread were estimated.

Surface treatments were performed on single-crystal semi-insulating 6H–SiC by femtosecond pulsed laser irradiation, aimed at analyzing the effect of the laser-induced periodic surface structures (LIPSSs) on the films’ optical properties. The surface morphology study of the laser-induced nanostructures allows determining the modification threshold fluence of about 0.7 J cm−2 as well as detecting fine (160 nm) and coarse (450–550 nm) ripples according to different values of the laser pulse fluence (ΦP) released to the material. Micro-Raman spectroscopy allows determining the presence of undesired amorphous structural phases when ΦP exceeds 2.15 J cm−2, whereas no compositional variations occur for lower values of ΦP. Samples treated on the entire surface with the pulse fluence conditions to obtain fine ripples were optically tested. Although the long-range order is progressively lost as the accumulated laser fluence increases, the heaviest treated samples show solar absorptance values > 75% and spectral selectivity up to 1.7 projected at the operating temperature of 1000 K, thus pointing out the suitability of fs-laser surface textured 6H–SiC to act as a selective solar absorber for energy conversion devices operating at high temperature.

Proton beams of 7 MeV energy, produced by a linear accelerator, were used to irradiate LiF crystals and thin films thermally evaporated on glass substrates in the dose range from 10 3 to 4 × 10 6 Gy, inducing the formation of stable photoluminescent colour centres (mainly F 2 and F 3 + ), emitting in the visible spectral range. Using a conventional fluorescence microscope, the transversal proton beam intensity was mapped by acquiring the photoluminescence image of the irradiated spots. Image analysis allowed measuring the integrated photoluminescence intensity as a function of the irradiation dose: a linear optical response was obtained up to different maximum dose values, after which a quenching was observed, depending on the nature of the samples (crystals or films). The colour centres formation was investigated by optical absorption spectroscopy at room temperature and the Principal Component Analysis was applied to the absorption spectra of irradiated LiF crystals. In samples irradiated at highest doses, it allowed clearly identifying the formation of more complex aggregate defects, which appears strictly related to the observed photoluminescence quenching effect.

Intensity Modulated Proton Therapy (IMPT) can take great advantage of fast tools based on analytical or semianalytical approaches providing dose evaluation in a target. Here, a semianalytical method is described that has been developed for the TOP-IMPLART (Intensity Modulated Proton Linear Accelerator for RadioTherapy) accelerator, consisting of a pulsed full linear accelerator for proton therapy being developed at ENEA Frascati, where preliminary tests of active beam energy and intensity modulation are undergoing. The method relies on a two-step procedure that provides the main accelerator parameters and optimizes the number and the weights of the energetic components needed to obtain a uniform Spread-Out Bragg Peak (SOBP) in the target region. In the present paper, the theoretical basis of the method is described in detail together with two practical example applications.

We present the study of optical and spectral properties of radiation-induced stable point defects, known as color centers (CCs), in lithium fluoride (LiF) for the detection of 10 keV XFEL beam at Spring-8 Angstrom Compact free electron LAser (SACLA) in Japan. A thick LiF crystal was irradiated in four spots with 10 keV XFEL beam (pulse duration = 10 fs) with different number of accumulated shots. After irradiation the colored-LiF spots were characterized with an optical microscope in fluorescence mode and their photoluminescence intensity and spectra were analyzed.

This contribution to ECPD2019 is dedicated to the memory of Anatoly Faenov. During a period of approximately thirteen years 1994–2006, Anatoly and his wife Tatiana Pikuz (simply “Tania” for friends), accepting the frequent invitations of the National Institute for Nuclear Physics (INFN) and of the Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), cooperated with many Italian research laboratories dedicated to EUV and soft X-ray generation, spread in different towns (L'Aquila, Frascati, Milano, Padova, Pisa, Roma, etc.). In spite of the fact that they could stay in Italy only about one or two months per year, their activity was so intense that more than 50 peer- reviewed publications were generated from their experimental and theoretical work (just considering only the results obtained at L'Aquila and Tor Vergata—Rome Universities and at the ENEA Research Center of Frascati), without mentioning the cultural atmosphere that they stimulated in the field of Science and Humanity. The numerous experimental spectra obtained at ENEA by means of their spherically bent mica spectrometers, together with the corresponding theoretical simulations performed in Moscow, allowed to study the changing role of different excitations mechanisms for various plasma conditions, and to characterize at best the ENEA laser-plasma source for different applications: polychromatic and monochromatic micro-radiography of dried biological samples at 1 keV, soft X-ray contact microscopy (SXCM) of living cells in the water-window spectral region, spectroscopy of hollow atoms, etc. In this memorial paper, the main results of biological samples imaging on lithium fluoride (LiF) detectors, obtained with the ENEA and Tor Vergata University laser-plasma sources, are presented. In particular, the improvement of the micro-radiography and of the SXCM techniques obtained after moving from photoresist detectors and photographic films to lithium fluoride (LiF) detectors are discussed, for both dried and wet biological samples.

In a recent paper, an analytical expression for proton Bragg curves was introduced and utilized to best fit photoluminescent depth distributions of optically active F 2 and F 3 + color centers in lithium fluoride, with the purpose of evaluating the energy spectrum of a proton beam, assumed to consist of the superposition of Gaussian components. Here, an original alternative method is introduced by means of which the same energy spectrum analysis can be performed by iteratively applying a suitable mathematical operator to the photoluminescent depth distribution, no best fitting operation being needed.

In the framework of the Italian TOP-IMPLART project (Regione Lazio), ENEA-Frascati, ISS and IFO are developing and constructing the first proton linear accelerator based on an actively scanned beam for tumor radiotherapy with final energy of 150 MeV. An important feature of this accelerator is modularity: an exploitable beam can be delivered at any stage of its construction, which allows for immediate characterization and virtually continuous improvement of its performance. Currently, a sequence of 3 GHz accelerating modules combined with a commercial injector operating at 425 MHz delivers protons up to 35 MeV. Several dosimetry systems were used to obtain preliminary characteristics of the 35-MeV beam in terms of stability and homogeneity. Short-term stability and homogeneity better than 3% and 2.6%, respectively, were demonstrated; for stability an improvement with respect to the respective value obtained for the previous 27 MeV beam.

Luminescence properties of point defects in insulating materials are successfully used for solid state light sources and radiation detectors. Among them, colour centres in lithium fluoride, LiF, are well known for their application in tuneable lasers and dosimeters. Broad-band light-emitting F2 and F3+ electronic defects, stable at room temperature, are produced in LiF crystals and films by different kinds of radiation. Under blue optical pumping in their overlapping absorption bands, the efficient photoluminescence spans over the green-red visible spectral range. Novel LiF thin-film radiation imaging detectors based on the exploitation of the peculiar spectral characteristics of F2 and F3+ defects and of the optical properties and radiation sensitivity of the LiF material have been proposed and successfully tested for extreme ultraviolet radiation, soft and hard X-ray imaging, including micro-radiography of biological objects, even for in vivo samples. After exposure to X-rays, the latent images stored in the LiF thin layers by local formation of active defects are read with conventional and advanced optical fluorescence microscopes. Among the main advantages of the LiF thin-film imaging detectors, there are intrinsic very high spatial resolution, large field of view and wide dynamic range. Moreover, these solid state radiation detectors are easy to handle, as insensitive to ambient light, and no development process is needed. Recently their use has been extended to proton beam advanced diagnostics. In this paper, a short review of their properties, results and applications in X-ray biological imaging and proton dose-mapping is presented, underlying the great versatility and potentialities offered by LiF thin films, whose photoluminescence response can be improved through the choice of suitable substrates and growth conditions. © 2015 Elsevier B.V. All rights reserved.

Novel X-ray imaging detectors based on photoluminescence of colour centres in lithium fluoride (LiF) have been proposed and tested for extreme ultraviolet, soft and hard X-rays up to 10 keV. For the first time we present the optical characterisation of LiF crystals and thin films irradiated at the TOPO-TOMO beamline of synchroton light source Anka (Karlsruhe, Germany) in the energy range 6-40 keV for different exposure times. Absorption and photoluminescence spectra were analysed to study the optical response of the LiF-based detectors. High resolved X-ray imaging of commercial test patterns has been obtained on LiF crystals and films by optical readout with a confocal laser scanning fluorescence microscope. © 2012 Elsevier B.V.

Purpose: To study EBT3 GafChromic film in low-energy protons, and for comparison purposes, in a reference 60Co beam in order to use it as a calibrated dosimetry system in the proton irradiation facility under construction within the framework of the Oncological Therapy with Protons (TOP)-Intensity Modulated Proton Linear Accelerator for RadioTherapy (IMPLART) Project at ENEA-Frascati, Italy. Methods: EBT3 film samples were irradiated at the Istituto Nazionale di Fisica Nucleare—Laboratori Nazionali di Legnaro, Italy, with a 5 MeV proton beam generated by a 7 MV Van de Graaff CN accelerator. The nominal dose rates used were 2.1 Gy/min and 40 Gy/min. The delivered dose was determined by measuring the particle fluence and the energy spectrum in air with silicon surface barrier detector monitors. A preliminary study of the EBT3 film beam quality dependence in low-energy protons was conducted by passively degrading the beam energy. EBT3 films were also irradiated at ENEA-National Institute of Ionizing Radiation Metrology with gamma radiation produced by a 60Co source characterized by an absorbed dose to water rate of 0.26 Gy/min as measured by a calibrated Farmer type ionization chamber. EBT3 film calibration curves were determined by means of a set of 40 film pieces irradiated to various doses ranging from 0.5 Gy to 30 Gy absorbed dose to water. An EPSON Expression 11000XL color scanner in transmission mode was used for film analysis. Scanner response stability, intrafilm uniformity, and interfilm reproducibility were verified. Optical absorption spectra measurements were performed on unirradiated and irradiated EBT3 films to choose the most sensitive color channel to the dose range used. Results: EBT3 GafChromic films show an under response up to about 33% for low-energy protons with respect to 60Co gamma radiation, which is consistent with the linear energy transfer dependence already observed with higher energy protons, and a negligible dose-rate dependence in the 2–40 Gy/min range. Short- and long-term scanner stabilities were 0.5% and 1.5%, respectively; film uniformity and reproducibility were better than 0.5%. Conclusions: The main purpose of this study was to implement EBT3 dosimetry in the proton low-energy radiobiology line of the TOP-IMPLART accelerator, having a maximum energy of 7 MeV. Low-energy proton and 60Co calibrated sources were used to investigate the behavior of film response vs to be written in italicum dose. The calibration in 5 MeV protons is currently used for dose assessment in the radiobiological experiments at the TOP-IMPLART accelerator carried out at that energy value.

The first proton linear accelerator for tumor therapy based on an actively scanned beam up to the energy of 150 MeV, is under development and construction by ENEA-Frascati, ISS and IFO, under the Italian TOP-IMPLART project. Protons up to the energy of 7 MeV are generated by a customized commercial injector operating at 425 MHz; currently three accelerating modules allow proton delivery with energy up to 27 MeV. Beam homogeneity and reproducibility were studied using a 2D ionizing chamber, EBT3 films, a silicon diode, MOSFETs, LiF crystals and alanine dosimetry systems. Measurements were taken in air with the detectors at ~1 m from the beam line exit window. The maximum energy impinging on the detectors surface was 24.1 MeV, an energy suitable for radiobiological studies. Results showed beam reproducibility within 5% and homogeneity within 4%, on a circular surface of 16mm in diameter. © The Author(s) 2018.

Colour centres (CCs) in lithium fluoride (LiF) are well known for application in tuneable lasers and dosimeters. The visible photoluminescence (PL) of radiation-induced, broad-band light-emitting aggregate CCs in LiF crystals and films has been proposed for high spatial resolution X-ray imaging; use of LiF-based detectors has been recently successfully extended to advanced diagnostics of low-energy proton beams. After exposure, transversal dose mapping was obtained on LiF films by acquiring the visible PL image of the irradiated spots in a fluorescence microscope under blue-light pumping. Irradiation of thermally evaporated LiF thin films with a proton beam of 3 MeV nominal energy, produced by a linear accelerator, in the fluence range of 1011–1015 protons/cm2, induces the formation of stable CCs, mainly the primary F centre and the aggregate F2 and F3 + defects. A comparison with irradiations performed at 7 MeV shows that the spectrally integrated PL as a function of the absorbed dose is independent on the selected beam energy, at least as far as typical LiF film thicknesses are concerned. The PL behaviour vs. dose can be described by a linear growth which covers up to three order of magnitude, followed by saturation at high values (> ≈105 Gy). The spectral contributions of F2 and F3 + CCs to the detected PL, in the red and in the green respectively, under laser pumping were carefully analysed in order to investigate behaviour differences of these defects at high doses. © 2018 Elsevier B.V.

Summary 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 obtainedutilizingX-rayradiationinthewaterwindowenergy rangefromalaserplasmasource.Theusedmethodisbasedon loading of the samples, the cell suspension, in a special holder wheretheyareinclosecontactwithaLiFcrystalsolid-stateXrayimagingdetector.Afterexposureandsampleremoval,the imagesstoredinLiFbythesoftX-raycontactmicroscopytechniquearereadbyanopticalmicroscopeinfluorescencemode. 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 peculiaritiesoftheusedX-rayradiationandoftheLiFimaging detectorallowobtainingimagesinabsorptioncontrastrevealing the internal structures of the investigated samples at high spatialresolution.Moreover,thewidedynamicrangeoftheLiF imagingdetectorcontributestoobtainhigh-qualityimages.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.

Proton beams of 3 and 7 MeV energies, produced by a linear accelerator, were used to irradiate lithium fluoride crystals and thermally evaporated LiF thin films in the fluence range of 1011-1015 protons/cm2. The irradiation induces the formation of stable colour centres, mainly the primary F centre and the aggregate F2 and F 3 + defects. By optical pumping in the blue spectral region, the F2 and F3 + centres emit broad photoluminescence bands in the visible spectral range. By conventional fluorescence microscopy, the integrated photoluminescence intensity was carefully measured in LiF crystals and thin films as a function of the irradiation fluence: a linear optical response was obtained in a large range of fluence, which is dependent on the used LiF samples and the selected beam energy. It was possible to record the transversal proton beam intensity profile by acquiring the photoluminescence image of the irradiated spots on LiF films by a standard optical microscope. Using LiF films grown on silicon substrates irradiated in a particular geometry, the same optical reading microscopy technique allowed one to measure the distribution of colour centres photoluminescence along the depth and direct imaging the Bragg peak position, which gives a rough estimation of the initial proton beam energy.© 2014 Published by Elsevier B.V.

Planar active waveguides were produced in lithium fluoride crystals by implantation with 1.5 MeV He + ions at several doses. The colored samples have been characterized by optical absorption, photoluminescence and m-line spectroscopy. By comparing the measured guided-mode effective indices with the ones calculated by means of the Chandler–Lama approach, the depth profile of refractive index was derived, showing that there are two competitive physical mechanisms, associated with different processes of energy deposition along the ion track, responsible for positive and negative modifications of the refractive index in the irradiated volume.

Solid-state radiation detectors based on the photoluminescence of stable point defects in lithium fluoride crystals have been used for advanced diagnostics during the commissioning of the segment up to 27 MeV of the TOP-IMPLART proton linear accelerator for proton therapy applications, under development at ENEA C.R. Frascati, Italy. The LiF detectors high intrinsic spatial resolution and wide dynamic range allow obtaining two-dimensional images of the beam transverse intensity distribution and also identifying the Bragg peak position with micrometric precision by using a conventional optical fluorescence microscope. Results of the proton beam characterization, among which, the estimation of beam energy components and dynamics, are reported and discussed for different operating conditions of the accelerator. © 2017 Elsevier B.V.

Irradiation of lithium fluoride (LiF) crystals by low energy (few keV) electron beams gives rise to the efficient formation of stable laser active colour centres, mostly F2 and F3+ aggregate defects, on their surface. The presence of primary and aggregate point defects induces a local increase of the refractive index of the thin irradiated layer in the green-red spectral range, where the F3+ and F2 visible emissions are located. The use of electron-beam lithography techniques allows for the definition of coloured strips, so miniaturised optical active channel waveguides may be fabricated by a direct-writing process. We report on the observation of amplified spontaneous emission of the red light from LiF:F2 centres in active waveguides realised with different irradiation doses in a LiF crystal, in order to determine the influence of this fundamental parameter on the amplification properties of these optical confining structures. Low pumping power densities have been used in quasi-continuous-wave regime at room temperature; the appreciable values of the gain coefficient, several cm−1, with an exciting power density of few hundreds mW/cm2, make this material a good candidate for the realisation of active integrated optical devices.

We report about the light-emitting properties of colour centres in lithium fluoride thin films and crystals treated with low-penetrating extreme-ultraviolet radiation and soft X-rays. Experimental fluorescence-imaging results show that, under the same irradiation conditions, stronger photoluminescence, up to a factor eight, is released by colour centres in a film thermally grown on silicon substrate than in a crystal. By using a classical-electromagnetism model, we take into account the role of the silicon substrate in the enhancement of spontaneous emission over a broad spectral range to analyze such behaviour.

Large and transparent LiF:Pb and LiF:Tl crystals were successfully grown by using Kyropoulos method. They were characterized using spectroscopic measurements combined with differential thermal analysis and thermogravimetry (TG) analysis, in order to investigate the effect of dopants upon the optical properties of these crystals. The optical absorption peaks at 278 nm (for Pb) and 273 nm (for Tl) have been assigned to the A-type transition of these ions. Photoluminescence spectra have shown bands at 350 nm (for Tl) and 375 nm (for Pb), which have been associated to the dopant ions in different configurations in the lattice.

The use of LiF thin films and single crystals was proposed and tested as X-ray imaging detector based on optically stimulated luminescence from visible-emitting color centers. The main peculiarities of this detector – i.e. high spatial resolution on a large field of view, wide dynamic range, versatility and simplicity of use – make it very promising as X-ray imaging plate for applications in photonic devices, biology and material science, as well as in the characterization of intense X-ray sources. In order to investigate the response and the sensitivity of this detector to soft X-rays, a suitable characterization of colored thin layers is performed by means of optical spectrophotometry and photoluminescence spectroscopy for samples colored under different irradiation conditions.

The influence of Pb 2+ doping on the optical properties of LiF crystals before and after irradiation with X-ray was studied by using optical absorption and photoluminescence measurements. After irradiation it was observed an increase of the absorption due to primary and aggregate electronic defects together with a higher photoluminescence signals associated with the F 2 and F 3 + colour centres in doped samples compared with the undoped ones.

A theoretical model to evaluate normal-incidence specular, direct, hemispherical, and diffuse reflectance and transmittance of a single layer affected by refractive-index inhomogeneity along the growth axis, roughness, and thickness wedge was introduced in recent papers. In the present work, the model is extended to the case of a multilayer optical coating. To that purpose, suitable transfer matrices that account for layer-index inhomogeneity and random deviations of the interfaces from smooth planes are introduced, and statistical averages are applied to the resulting amplitude and intensity coefficients. Eventually, thickness wedge is included as a deterministic average on the intensity coefficients.

We present broadband X-ray lensless projection imaging experiments performed at the TopoTomo beamline of the ANKA synchrotron facility by using innovative solid-state detectors based on the formation of stable photoluminescent colour centres (CCs) in lithium fluoride (LiF) films and crystals. The peculiar features of these detectors, like very high spatial resolution (standard 250 nm) across a large field of view (> 1 cm2), wide dynamic range (> 103), versatility and easiness of use combined with the high sensitivity of the optical fluorescence microscopy reading technique, make them very attractive as recording plates for X-ray imaging. High-resolution X-ray images of a metallic test pattern were recorded and acquired with good contrast both in LiF crystals and thin LiF films. The stored CCs fluorescence images show edge-enhancement effects ascribable to diffraction processes occurring during the X-ray beam propagation after its interaction with the samples. The experimental data concerning films and crystals based LiF-detectors will be discussed and compared with computer simulations of X-ray intensity distributions. The LiF film performances are very encouraging for the exploitation of these solid-state detectors for X-ray lensless imaging applications.

Fluorescent lithium fluoride detectors for X-ray projection imaging F. Bonfigli, M.A. Vincenti, R.M. Montereali ENEA, C.R. Frascati, Photonics Micro- and Nano-structures Lab., UTAPRAD-MNF, Via E. Fermi 45, 00044 Frascati (Rome), Italy E. Nichelatti ENEA, C.R. Casaccia, Optical Devices Laboratory, UTTMAT-OTT, Via Anguillarese 301, 00123 S. Maria di Galeria, Rome, Italy F. Somma, S. Heidari Bateni Università degli Studi Roma Tre, Dip. di Fisica E. Amaldi, Via della Vasca Navale 84, 00146 Rome, Italy A. Cecilia, T. Baumbach Institute for Photon Science and Synchrotron Radiation (IPS)/ANKA, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany. Abstract The possibility of detecting high quality images of materials, devices and biological samples in the soft and hard X-ray spectral ranges with high spatial resolution and contrast and by using simple exposing configuration is a topical task nowadays. For this purpose, we propose the use of versatile imaging detectors based on the radiation sensitivity of lithium fluoride (LiF) to extreme ultraviolet, soft and hard X-rays [1, 2]. X-rays generate stable point defects in LiF, known as colour centres (CCs), which emit broad-band photoluminescence at visible wavelengths under optical pumping. The high dynamic response of the material to the received dose together with the atomic scale of the CCs make LiF plates, in form of thin films or crystals, extremely attractive as high-spatial-resolution radiation-imaging detectors both in absorption and phase contrast imaging configurations [1, 3]. The latent images are subsequently read by using optical fluorescence microscopes, which in the case of advanced techniques can reach spatial resolutions well below 100 nm [4]. We present lensless imaging experiments in projection mode at the TOPO–TOMO beamline of the synchrotron light source Anka (Karlsruhe, Germany) by using LiF crystals and thin films irradiated in the energy range 6–40 keV. Stable fluorescent images were formed in LiF detectors by scattered X-rays after an object had been positioned between the X-ray source and the detectors. The object used in this work is the commercial test pattern X500-200-30 (Xradia, Pleasanton, CA, USA) consisting of a gold mask (thickness 3 m) deposited on a (500500) μm2 Si3N4 window (thickness 330 nm). The LiF detectors were crystals and 1 m thick polycrystalline films deposited on glass substrates. To imprint the X-ray image of the sample on the LiF detectors, the test pattern was irradiated with several exposure times between 1 s and 60 s. The X-ray micro-radiographies were optically read with a confocal laser scanning microscope (CLSM, Nikon Eclipse 80i-C1) operating in fluorescence mode. It is worth pointing out that a 1 m LiF film was able to store high-quality and well contrasted fluorescence images of the test pattern, although X-ray attenuation length in LiF varies between 0.02-12 mm for X-ray energies in the investigated range. The stored images show edge-enhancement effects that are ascribable to diffraction processes occurring during the X-ray beam propagation after its interaction with the sample. A computer simulation was performed to calculate the incoming X-ray intensity distribution across the detector. A fairly good agreement with experimental data evidences a linear optical fluorescence response of LiF-film based detectors under the investigated conditions. This linear behaviour has been confirmed by measurements of the PL signals of F2 and F3+ CCs detected with a CLSM system for several X-ray irradiation times. Further investigations are in progress to study the exploitation of solid-state LiF detectors for X-ray lensless projection imaging experiments and applications. References [1] G. Baldacchini, F. Bonfigli, A. Faenov, F. Flora, R.M. Montereali, A. Pace, T. Pikuz, L. Reale, J. Nanoscience and Nanotechnology 3, 6 483-486, (2003). [2] S. Almaviva, F. Bonfigli, I. Franzini, A. Lai, R.M. Montereali, D. Pelliccia, A. Cedola, S. Lagomarsino, Appl. Phys. Lett. 89, 54102, (2006). [3] F. Bonfigli, A. Cecilia, S. Heidari Bateni, E. Nichelatti, D. Pelliccia, F. Somma, P. Vagovic, M.A. Vincenti, T. Baumbach and R.M. Montereali, Radiation Measurements 56, 277-280, (2013). [4] A. Ustione, A. Cricenti, F. Bonfigli, F. Flora, A. Lai, T. Marolo, R.M. Montereali, G. Baldacchini, A. Faenov, T. Pikuz, L. Reale, Appl. Phys. Lett. 88, 141107 (2006).

An innovative diamond detector layout is presented that is designed to operate at high temperature under intense neutron and gamma fluxes. It is made of a 500 μm "electronic grade" diamond film with 100 nm thick Ag metal contacts deposited onto each surface of the film by means of thermal evaporation. A 2μm thick layer of 6LiF has been deposited on top of one of the two Ag contacts to make the detector sensitive to thermal neutrons. The device was tested at the ISIS spallation neutron source (Rutherford Appleton Laboratory, UK) using the INES beam line. The detector was continuously irradiated for 100 hours in vacuum (p = 10-5 mbar), exposed to a neutron flux of about 106 n cm-2 s-1 at a temperature T = 150°C. The aim of this experiment was to study the time dependence of the diamond detector performance while operating at high temperature under irradiation, providing a first experimental proof of reliable continuous operation for 100 hours at high temperature in a harsh environment. Copyright © EPLA, 2016.

We present a marking technology which uses extreme ultraviolet radiation to write invisible patterns on tags based on alkali fluoride thin films. The shape of the pattern is pre-determined by a mask (in the case of contact lithography) or by a suitable mirror (projection lithography). Tags marked using this method offer a much better protection against fakes than currently available anti-counterfeiting techniques. The complexity and cost of this technology can be tailored to the value of the good to be protected, leaving, on the other hand, the specific reading technique straightforward. So far, we have exploited our invisible marking to tag artworks, identity cards, electrical components, and containers of radioactive wastes. Advantages and limits of this technology are discussed in comparison with the anti-counterfeiting systems available in the market. © 2016 IOP Publishing Ltd and Sissa Medialab srl.

Nuclear instruments & methods in physics research / A 833, 68 - 76(2016). doi:10.1016/j.nima.2016.07.005, The white beam (∼6–80 keV) available at the TopoTomo X-ray beamline of the ANKA synchrotron facility (KIT, Karlsruhe, Germany) was used to perform edge-enhancement imaging tests on lithium fluoride radiation detectors. The diffracted X-ray image of a microscopic boron fibre, consisting of tungsten wire wrapped by boron cladding, was projected onto lithium fluoride thin films placed at several distances, from contact to 1m. X-ray photons cause the local formation of primary and aggregate colour centres in lithium fluoride; these latter, once illuminated under blue light, luminesce forming visible-light patterns—acquired by a confocal laser scanning microscope—that reproduce the intensity of the X-ray diffracted images. The tests demonstrated the excellent performances of lithium fluoride films as radiation detectors at the investigated photon energies. The experimental results are here discussed and compared with those calculated with a model that takes into account all the processes that concern image formation, storing and readout., Published by Elsevier, Amsterdam

We present experimental results on simultaneous surface nanostructuring and optical activation of lithium fluoride crystals by 800 eV off-normal Ar + sputtering. Our data demonstrate that the formation of periodic nanostructures is accompanied by the efficient production of stable electronic defects, optically active in the green and red parts of the visible spectra, thus providing the possibility to conceive and fabricate advanced insulating substrates.

Broad-band visible-emitting micro-strips were induced in Lithium Fluoride crystals by direct writing with a monochromatic soft X-ray beam. They were successfully characterized via fluorescence imaging, photoluminescence and optical transmittance. The irradiation gave rise to stable primary and aggregate color centers within a thin surface layer of the crystals. Their volume concentrations were evaluated together with the induced modification of the complex refractive index in the irradiated volume.

A confocal laser scanning microscope has been used in a non-conventional approach to reconstruct the depth distribution of stable, optically active color centers induced at the surface of a lithium fluoride crystal by a low energy electron beam. The formation of F2 and F 3 + aggregate electronic defects was limited to the penetration depth of the electrons in the material, as obtained from Monte Carlo simulations. This novel measurement technique could be easily used for spatial characterization of luminescent optical waveguides in transparent dielectrics.

Processes of radiation creation and annealing of Frenkel defects, as well as their transformation processes, have been studied in γ -irradiated LiF single crystals containing various impurities, by means of measurements of thermally stimulated changes in absorption and emission spectra. Important information about the density of colour centres in LiF, which depends on γ -irradiation doses, impurities and temperatures, has been obtained for small crystal contents of oxygen, hydroxyl and metal ions. A comparison of annealing parameters of the LiF crystals subjected to different doses of irradiation, but to the same thermal bleaching procedures, has been performed and the results are critically discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Light emitted when heating crystalline materials previously exposed to ionizing radiation is commonly known as thermoluminescence. The resultant glow curve is related to the material, the impurities and the defect centers generated by the irradiation. Several efforts have been made in the past to associate glow peaks with specific defect centers. Recently, in the case of LiF we established a link between F3+ and F3 centers and the temperature region of the glow curve below 200 °C. This result was obtained by using especially treated samples with known concentration of color centers in first place, and annealing measurements in second place. By continuing these studies, it has been possible to establish a further link between F2 centers and a prominent feature of the glow curve near 260 °C. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Permanent bleaching of F and F2 color centers in gamma irradiated lithium fluoride crystals has been obtained under low power, CW laser illumination at 244 nm. Optical absorption and photoluminescence measurements reveal a selective change in the concentrations of these kinds of electronic defects. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The use of efficient wavelength-shifters from the vacuum-ultraviolet to the photo-sensor'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.© 2013 IOP Publishing Ltd and Sissa Medialab srl.

To study EBT3 GafChromic film in low-energy protons, and for comparison purposes, in a reference (60)Co beam in order to use it as a calibrated dosimetry system in the proton irradiation facility under construction within the framework of the Oncological Therapy with Protons (TOP)-Intensity Modulated Proton Linear Accelerator for RadioTherapy (IMPLART) Project at ENEA-Frascati, Italy.EBT3 film samples were irradiated at the Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali di Legnaro, Italy, with a 5 MeV proton beam generated by a 7 MV Van de Graaff CN accelerator. The nominal dose rates used were 2.1 Gy/min and 40 Gy/min. The delivered dose was determined by measuring the particle fluence and the energy spectrum in air with silicon surface barrier detector monitors. A preliminary study of the EBT3 film beam quality dependence in low-energy protons was conducted by passively degrading the beam energy. EBT3 films were also irradiated at ENEA-National Institute of Ionizing Radiation Metrology with gamma radiation produced by a (60)Co source characterized by an absorbed dose to water rate of 0.26 Gy/min as measured by a calibrated Farmer type ionization chamber. EBT3 film calibration curves were determined by means of a set of 40 film pieces irradiated to various doses ranging from 0.5 Gy to 30 Gy absorbed dose to water. An EPSON Expression 11000XL color scanner in transmission mode was used for film analysis. Scanner response stability, intrafilm uniformity, and interfilm reproducibility were verified. Optical absorption spectra measurements were performed on unirradiated and irradiated EBT3 films to choose the most sensitive color channel to the dose range used.EBT3 GafChromic films show an under response up to about 33% for low-energy protons with respect to (60)Co gamma radiation, which is consistent with the linear energy transfer dependence already observed with higher energy protons, and a negligible dose-rate dependence in the 2-40 Gy/min range. Short- and long-term scanner stabilities were 0.5% and 1.5%, respectively; film uniformity and reproducibility were better than 0.5%.The main purpose of this study was to implement EBT3 dosimetry in the proton low-energy radiobiology line of the TOP-IMPLART accelerator, having a maximum energy of 7 MeV. Low-energy proton and (60)Co calibrated sources were used to investigate the behavior of film response vs to be written in italicum dose. The calibration in 5 MeV protons is currently used for dose assessment in the radiobiological experiments at the TOP-IMPLART accelerator carried out at that energy value.

A thin film of Tetraphenyl-butadiene (TPB) deposited onto the surface delimiting the active volume of the detector and/or onto the photosensor's optical window is the most common solution to down convert argon VUV scintillation light in current and planned liquid argon based experiments for dark matter searches and neutrino physics. Characterization of the main features of TPB coatings on different, commonly used substrates is reported, as a result 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.© 2013 IOP Publishing Ltd and Sissa Medialab srl.

The depth refractive index profiles of broadband visible-emitting planar waveguides produced in LiF crystals with 1.5- and 2-MeV He+ ions at different doses have been derived from mode analysis. They show that there are two competitive mechanisms responsible for positive and negative modifications of the refractive index in the irradiated volume associated with different processes of energy deposition of the incident ions, so as to induce a complex coloration profile along the penetration direction, which is strongly dependent on the irradiation dose.

Point defects in lithium fluoride (LiF) have recently attracted renewed attention due the exciting results obtained in the realisation of miniaturised optical devices. Among light-emitting materials, LiF is of particular interest because it is almost not hygroscopic and can host, even at room temperature, stable color centers (CCs) that emit light in the visible and in the near infrared spectral range under optical excitation. The increasing demand for low-dimensionality photonic devices imposes the use of advanced irradiation methods for producing luminescent structures with high spatial resolution. An innovative irradiation technique to produce luminescent CCs in LiF crystals and films by using an extreme ultra-violet and soft X-ray laser-plasma source will be presented. This technique is capable to induce colored patterns with submicrometric spatial resolution on large areas in a short exposure time as compared with other irradiation methods. Luminescent regular arrays produced by this irradiation technique will be shown. Recently, the idea of using a LiF film as image detector for X-ray microscopy and micro-radiography based on optically-stimulated luminescence from CCs has been developed.

The spectral identification of several photoluminescent defects produced in LiF by ionising radiation is still uncertain because many optical transitions are possible and their different spectral features are often overlapping. Performing a conventional spectroscopic characterization requires a lot of time and intuition, but recently a more effective investigation method has been developed: combined excitation-emission spectroscopy (CEES). In this approach a large number of excitation (or emission) spectra is recorded at a sequence of emission (or excitation) wavelengths. The resulting three-dimensional data set of excitation intensities as a function of excitation and emission wavelengths, or energies, is visualized using a contour plot, where lines of equal emission intensities are drawn. For the first time this method has been successfully applied to coloured LiF crystals and films. As an example, the case of visible-emitting colour centres, absorbing in the M band spectral region in a gamma irradiated LiF crystal is reported and discussed. Spectroscopic features of well-known active defects have been confirmed, more complex centres clearly identified and other properties better clarified. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A great effort in X-ray imaging studies has been dedicated to the design of novel optics-detector solutions that aims in creating a compact laboratory X-ray microscopy apparatus. Based on our experience in the use of both capillary/polycapillary optical systems and LiF imaging detectors we have recently tested a new combination of these techniques. The potential of the optics both to concentrate and to shape X-ray radiation enforced by the high performances in terms of spatial resolution/dynamic range of LiF imaging detectors allows us to use very simple imaging techniques, like the contact one, particularly suitable for compact imaging systems. In this paper we present first results about high spatial resolution images of transmitted X-rays through a polycapillary semi-lens. Submicron X-ray imaging of thick geological samples was also presented and discussed. These results demonstrate the potentialities of these novel X-ray imaging system for characterization of X-rays optics and for applications in material, life and heart sciences. © 2012 Elsevier B.V.

The extreme ultraviolet radiation emitted by a laser-plasma source or by a capillary discharge laser is applied to the generation of luminescent patterns in lithium fluoride. This novel technique is able to produce colored patterns with high spatial resolution on large (more than 10 cm/sup 2/) areas in a short exposure time compared with other irradiation methods like the electron beam writing. The potentials of this technique for applications in photonics are commented. This work reviews the activity performed during the past four years at the ENEA Frascati Center and at L'Aquila University, Italy. Preliminary images of microradiography or X-ray contact microscopy using lithium fluoride as an imaging detector are presented. The advantages of this new detector compared with photographic films or with photoresists are discussed.