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We study the elasto-optic behavior of stressed cubic crystals (all classes) and isotropic materials (like e.g., glasses). We obtain the explicit dependence of the refraction indices on the stress (either applied or residual), as well as a mild generalization of the Brewster law for cubic crystals. We show also that the optic indicatrix and the stress ellipsoid are coaxial only in the isotropic case. This theory allows the improvement of the measurement techniques, as photoelasticity, on cubic crystals and optically isotropic materials.

In nuclear medicine, the gamma camera is one of the more used imaging devices for radionuclide imaging. Gamma camera provide an image of the target organ, with high spatial resolution and sensitivity; gamma cameras use collimators. This paper presents a simple and customizable collimator to be used in radionuclide imaging for preclinical studies, using additive manufacturing (AM) techniques. A numerical analysis, based on GATE Monte Carlo toolkit (vGate 8.2), has been conducted to simulate different configurations of an already working collimator used as reference. In addition to the standard collimator geometry with alternatives materials, we also propose a new concept of collimator to be easily 3D printed, using different 3D printing technologies. We have simulated collimators with square apertures of 1.5 mm and septa of 0.4 mm of thickness, source was Tc99m. The materials simulated were standard tungsten, a PLA doped with tungsten (Rapid 3D Shield Tungsten Filament - Virtual Foundry), a classical PLA filament and P A2200 for the new concept. The results show a similar behavior for what concern the spatial resolution, while for the sensitivity a reduction of about 45% of entries is reported. This is due mainly since the extruded pixel, made of PLA or PA2200, have higher density $(\approx$ 1.24 g/cm^3 for PLA and $\approx 0,95$ g/cm^3 for PA2200) with respect to air $(\approx$ 0,0012 g/cm^J). Further studies are necessary to explore optimization of the used design to reduce the impact of material density.

The antiproton experiment PANDA at FAIR is designed to bring hadron physics to a new level in terms of scope, precision and accuracy. In this work, its unique capability for studies of hyperons is outlined. We discuss ground-state hyperons as diagnostic tools to study non-perturbative aspects of the strong interaction, and fundamental symmetries. New simulation studies have been carried out for two benchmark hyperon-antihyperon production channels: $\bar{p}p \to \bar{\Lambda}\Lambda$ and $\bar{p}p \to \bar{\Xi}^+\Xi^-$. The results, presented in detail in this paper, show that hyperon-antihyperon pairs from these reactions can be exclusively reconstructed with high efficiency and very low background contamination. In addition, the polarisation and spin correlations have been studied, exploiting the weak, self-analysing decay of hyperons and antihyperons. Two independent approaches to the finite efficiency have been applied and evaluated: one standard multidimensional efficiency correction approach, and one efficiency independent approach. The applicability of the latter was thoroughly evaluated for all channels, beam momenta and observables. The standard method yields good results in all cases, and shows that spin observables can be studied with high precision and accuracy already in the first phase of data taking with PANDA., Comment: 26 pages, 16 figures. Changes: Revised title and abstract and corrections/clarifications in the text according to suggestions by journal referees

The European physical journal / A 57(4), 149 (2021). doi:10.1140/epja/s10050-021-00444-5, Published by Springer, Heidelberg

The Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, provides unique possibilities for a new generation of hadron-, nuclear- and atomic physics experiments. The future antiProton ANnihilations at DArmstadt (PANDA or $$\overline{\mathrm{P}}$$ P ¯ ANDA) experiment at FAIR will offer a broad physics programme, covering different aspects of the strong interaction. Understanding the latter in the non-perturbative regime remains one of the greatest challenges in contemporary physics. The antiproton–nucleon interaction studied with PANDA provides crucial tests in this area. Furthermore, the high-intensity, low-energy domain of PANDA allows for searches for physics beyond the Standard Model, e.g. through high precision symmetry tests. This paper takes into account a staged approach for the detector setup and for the delivered luminosity from the accelerator. The available detector setup at the time of the delivery of the first antiproton beams in the HESR storage ring is referred to as the Phase One setup. The physics programme that is achievable during Phase One is outlined in this paper.

In this work it is shown a precise way to optimize the heat generation in high viscosity magnetic colloids, by adjusting the Néel relaxation time in core/shell bimagnetic nanoparticles, for magnetic fluid hyperthermia (MFH) applications. To pursue this goal, Fe

In this work it is shown a precise way to optimize the heat generation in high viscosity magnetic colloids, by adjusting the Neel relaxation time in core/shell bimagnetic nanoparticles, for Magnetic Fluid Hyperthermia applications. To pursue this goal, Fe3O4/ZnxCo1-xFe2O4 core/shell nanoparticles were synthesized with 8.5 nm mean core diameter, encapsulated in a shell of ~1.1 nm of thickness, where the Zn atomic ratio (Zn/(Zn+Co) at%) changes from 33 at% to 68 at%. The magnetic measurements are consistent with a rigid interface coupling between the core and shell phases, where the effective magnetic anisotropy systematically decreases when the Zn concentration increases, without a significant change of the saturation magnetization. Experiments of magnetic fluid hyperthermia of 0.1 wt% of these particles dispersed in water, DMEM (Dulbecco modified Eagles minimal essential medium) and a high viscosity butter oil, result in a large specific loss power (SLP), up to 150 W/g, when the experiments are performed at 571 kHz and 200 Oe. The SLP was optimized adjusting the shell composition, showing a maximum for intermediate Zn concentration. This study shows a way to maximize the heat generation in viscous media like cytosol, for those biomedical applications that requiere smaller particle sizes .

Novel glasses and glass ceramics with compositions corresponding to stoichiometric lithium and barium disilicates and doped with different combinations of Ce3+, Eu2+,3+, Tb3+, and Dy3+ have been fabricated and studied as prospective light converters for white high-power light emitting diodes and laser diodes. Spatially resolved photoluminescence spectroscopy and structural analysis have been employed. The emission spectra and CIE color coordinates of these materials evidence their good prospective as phosphors for white light sources. Structural analysis proves a high level of crystallization of the ceramics fabricated by annealing the glasses, while spectroscopic study revealed the influence of crystallization on the emission properties of this system. The results show a high potential of these materials be exploited as temperature-resistant phosphors in high-power white light emitting diodes.

The mass production of new generations of high quality and very performant scintillating crystals requires sophisticated measurement systems and inspection tools in order to have reliable and precise data from such anisotropic materials. These measurement systems must be compatible with the industrial requirements and must be able to provide effective feedbacks aimed to the control of the crystals’ production quality. In this paper, a set of photoelasticity-based methods, solving the main limits of the presently available inspection systems, is presented. The main characteristics of such methods are the noninvasiveness, precision, and speed, which are well suited for their use in the industrial environment. This paper describes a set of measurement techniques and reports on real experimental data obtained on crystals having different cutting geometries with respect to the optic axes. The use of the proposed measurement methods, from laser conoscopy to laser sphenoscopy, along the optic axis and orthogonal to it, therefore provides a portfolio of noninvasive measurement techniques, and therefore, it is opening valuable space for the quality control of crystals in a production environment, optimizing important aspects such as the time duration of the inspection and its spatial resolution.

Nowadays, radiation detectors based on scintillating crystals are used in many different fields of science like medicine, aerospace, high-energy physics, and security. The scintillating crystals are the core elements of these devices; by converting high-energy radiation into visible photons, they produce optical signals that can be detected and analyzed. Structural and surface conditions, defects, and residual stress states play a crucial role in their operating performance in terms of light production, transport, and extraction. Industrial production of such crystalline materials is a complex process that requires sensing, in-line and off-line, for material characterization and process control to properly tune the production parameters. Indeed, the scintillators’ quality must be accurately assessed during their manufacture in order to prevent malfunction and failures at each level of the chain, optimizing the production and utilization costs. This paper presents an overview of the techniques used, at various stages, across the crystal production process, to assess the quality and structural condition of anisotropic scintillating crystals. Different inspection techniques (XRD, SEM, EDX, and TEM) and the non-invasive photoelasticity-based methods for residual stress detection, such as laser conoscopy and sphenoscopy, are presented. The use of XRD, SEM, EDX, and TEM analytical methods offers detailed structural and morphological information. Conoscopy and sphenoscopy offer the advantages of fast and non-invasive measurement suitable for the inspection of the whole crystal quality. These techniques, based on different measurement methods and models, provide different information that can be cross-correlated to obtain a complete characterization of the scintillating crystals. Inspection methods will be analyzed and compared to the present state of the art.

The physicists of the Polytechnic University of Marche (UNIVPM) have been conducting research in the physics of matter since the early seventies. Here we report a number of topics of the research activities carried out by the physicists working at the Department of Materials, Environmental Sciences and Urban Planning (SIMAU) of the Engineering Faculty, limiting our review to arguments and methods that are currently subject of investigation. The main scientific achievements and the most promising future developments are highlighted. The main purpose of this activity is the study of the macroscopic properties of matter in connection with its atomic structure for a variety of materials of technological interest in physics, chemistry, engineering, biology and medicine. These investigations require experimental tools capable of accessing the materials structure at the nanoscale. X-ray diffraction (XRD) and scattering techniques have represented the primary tool used to probe the structure of matter with atomic resolution, whereas electron microscopy techniques have provided complementary information on the structure and morphology of materials from the microscale down to the nanoscale. XRD studies have been performed using the X-ray instrumentation available at the departmental laboratories and, more recently, with the high-performance machines of the European synchrotron radiation facilities. Electron microscopy techniques have been implemented in an inter-departmental laboratory aimed at the structural and morphological characterization of soft and hard materials. The more recent set-up of laser optics laboratories has allowed an extended investigation of the properties of soft materials with focus on nonlinear optics of liquid crystalline and polymeric compounds.

The majority of instrumentation and systems for radiation detection are based on scintillators [...]

The great interest in scintillating crystals, is related to their applications in the high energy physics, biomedicine and security. For this reason a complete characterization and understanding of their structural, optical and mechanical properties at the macroscopic level is necessary. We must give a complete theoretical characterization of the mechanics and optics of bulk prismatic single-crystal bodies in order to design experiments. This work shall deal solely with the theoretical description within the framework of linear theories.

High temperature superconductor research is presently concentrated upon the flux pinning properties of the Abrikosov lattice of the mixed-mode superconducting phase. The temperature thermal fluctuations, current and magnetic field unpin the flux vortices and so cause electromagnetic resistivity in high temperature superconductors. Materials with higher vortex pinning exhibit less resistivity and are more attractive for industrial uses. In the present article, we measured and correlated the pinning flux energy barrier, determined by AC magnetic measurements, and transmission electron microscopy measurements to the critical current Jc in Yttrium- and Silver-doped MgB2 superconductors. The energy of the flux vortex was evaluated as a function of the magnetic field. The energy barrier curves suggest an optimal doping level to occur in doped materials. This result only depends on the optimal size and distribution of precipitates, and not on their chemical composition. The energy barriers have been compared with that of undoped MgB2 in literature.

Scintillating media are used in numbers of fields, from the high-energy physics to the biomedical devices, like those for the cancer detection and characterization, passing through the laser technology and industry processes control. Their performances must be enhanced in order to accomplish to the more and more sophisticated needs of the applications. Residual stress conditions are crucial for the correct performance of these materials. Moreover, an accurate study of the internal stress leads to a proper setting of the production process and prevent unwanted fractures of the brittle media. Non-invasive photoelastic methods are particularly suitable for the purpose; producing fringe pattern images which are a signature of the crystal state. These methods have to be supported of algorithms dedicated to the image analysis, so to extract geometrical parameters of the fringe pattern. Here an optimized algorithm to analyze the fringe pattern acquired by a laser based polariscope is discussed. This algorithm has been optimized and automated so to reduce the measurement uncertainty, considering a time saving procedure. The implemented procedure makes the software able to recognize the ROI in the acquired image and reduces the uncertainty by a factor 3.5.

The need for high-quality and high-performance crystals for high-energy physics (e.g. scintillators) and biomedical applications require a good knowledge of their mechanical and optical properties, amongst the others. This is a mandatory step in many quality control process aimed at the improvement of the technological processes for crystals growth. Following the first analysis already done for Tetragonal crystals, in this paper we study the elasto-optic behavior of optically biaxial (Monoclinic and Orthorhombic groups) and uniaxial crystals (Trigonal and Hexagonal groups). We evaluate the photoelastic constants, the optic angle and the optic plane associated to various states of stress, in terms of the components of the Piezo-Optic tensor.

In this work new energy storage components were prepared depositing films made of polyaniline (PANI) modified with gold/magnetite nanoparticles on flexible graphite foils. Three types of composite materials termed PANI/Fe3O4, PANI/Au/Fe3O4 and PANI/Au/Fe3O4@Yne (where @Yne is a propynylcarbamate group) were obtained by electrosynthesis. Galvanostatic charge-discharge (CD) and impedance tests (EIS) were performed to verify their efficiency in charge storage properties: for the gold-containing electrodes PANI/Au/Fe3O4 and PANI/Au/Fe3O4@Yne areal capacities values of 45.6 and 46.5 mAh cm(-2) were found in 0.5 M H2SO4 + 0.1 M LiCIO4 electrolyte solution at a current density of 0.5 mA cm(-2). These values are twofold higher than those found for PANI/Fe3O4 electrodes and fourfold greater than those for PANI alone (11.0 mAh cm(-2)). In turn PANI/Au/Fe3O4 and PANI/Au/Fe3O4@Yne were employed to assemble gel-state symmetric devices. CD, EIS and longtime resistance tests were made on the new devices that displayed an areal capacities of 100.0 mAh cm(-2) for PANI/Au/Fe3O4 and 73.6 mAh cm(-2) PANI/Au/Fe3O4@Yne respectively. To our knowledge this is the first time that AuNP-modified magnetite nanoparticles are used in energy storage devices preparation. (C) 2019 Elsevier Ltd. All rights reserved.

Among scintillators, the PWO is one of the most widely used, for instance in CMS calorimeter at CERN and PANDA project. Crystallographic structure and chemical composition as well as residual stress condition, are indicators of homogeneity and good quality of the crystal. In this paper, structural characterization of a defective PbWO4 (PWO) crystal has been performed by X-ray Diffraction (XRD), Energy Dispersive Spectroscopy (EDS) and Photoelasticity in the unusual a-c crystallographic plane. XRD and EDS analysis have been used to investigate crystallographic orientation and chemical composition, while stress distribution, which indicates macroscopic inhomogeneities and defects, has been obtained by photoelastic approaches, in Conoscopic and Sphenoscopic configuration. Since the sample is cut along the a-c crystallographic plane, a new method is proposed for the interpretation of the fringe pattern. The structural analysis has detected odds from the nominal lattice dimension, which can be attributed to the strong presence of Pb and W. A strong inhomogeneity over the crystal sample has been revealed by the photoelastic inspection. The results give reliability to the proposed procedure which is exploitable in crystals with other structures., Comment: 18 pages, 10 figures, revised version

Il documento sintetizza i risultati dello studio preliminare effettuato presso la cripta di Sant'Agnese in Agone (Roma), volto alla valutazione dei caratteri fisico-litologici dei materiali lapidei utilizzati per la realizzazione delle murature affrescate presenti nel sito e dell'impatto che può essere prodotto su queste ultime dalle condizioni microclimatiche indoor locali. Lo studio è stato commissionato all'Istituto di Metodologie Chimiche del Consiglio Nazionale delle Ricerche (IMC-CNR) da parte di EMASST (European Association of Material Surfaces Science and Technology), al fine di definire una pianificazione di massima delle attività necessarie alla conservazione degli affreschi contenuti nella cripta. Il rapporto si basa su valutazioni speditive effettuate nel corso di due sopralluoghi presso il sito da parte di personale di ricerca IMC-CNR specializzato in Scienze Geologiche e Tecnologie dei Materiali. Esso ha l'obiettivo di presentare le caratteristiche fisiche e chimico-mineralogiche macroscopicamente determinabili dei materiali lapidei utilizzati per la realizzazione delle murature, evidenziare criticità verso cui indirizzare indagini più accurate, suggerire opportuni protocolli di diagnosi sito specifici e soluzioni preliminari atte a migliorare le condizioni di conservazione degli affreschi. Per definire una possibile strategia finalizzata a mitigare gli impatti prodotti da agenti atmosferici e biotici indoor, il personale di IMC-CNR si è avvalso della collaborazione di ingegneri della Divisione Ricerca e Sviluppo del Settore Ambiente della società RI.EL.CO. Impianti S.r.l., di Rieti, che hanno accettato di visitare il sito.

Bimagnetic nanoparticles have been proposed for the design of new materials with controlled properties, which requires a comprehensive investigation of their magnetic behavior due to multiple effects arising from their complex structure. In this work we fabricated bimagnetic core/shell nanoparticles formed by an $\ensuremath{\sim}3$-nm antiferromagnetic (AFM) CoO core encapsulated within an $\ensuremath{\sim}1.5$-nm ferrimagnetic (FiM) ${\mathrm{Co}}_{0.5}{\mathrm{Ni}}_{0.5}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ shell, aiming at studying the enhancement of the magnetic anisotropy and the surface effects of a ferrimagnetic oxide shell. The magnetic properties of as-synthesized and annealed samples were analyzed by ac and dc magnetization measurements. The results indicate that the magnetic response of the as-synthesized particles is governed by the superparamagnetic behavior of the interacting nanoaggregates of spins that constitute the disordered ferrimagnetic shell, whose total moments block at $\ensuremath{\langle}{T}_{B}\ensuremath{\rangle}=49$ K and collectively freeze in a superspin-glass-type state at $\ensuremath{\langle}{T}_{g}\ensuremath{\rangle}=3$ K. On the other hand, annealed nanoparticles are superparamagnetic at room temperature and behave as an exchange-coupled system below the blocking temperature $\ensuremath{\langle}{T}_{B}\ensuremath{\rangle}=70$ K, with enhanced coercivity ${H}_{C}(10\phantom{\rule{4.pt}{0ex}}\text{K})\ensuremath{\sim}14.6$ kOe and exchange bias field ${H}_{EB}(10\phantom{\rule{4.pt}{0ex}}\text{K})\ensuremath{\sim}2.3$ kOe, compared with the as-synthesized system where ${H}_{C}(10\phantom{\rule{4.pt}{0ex}}\text{K})\ensuremath{\sim}5.5$ kOe and ${H}_{EB}(10\phantom{\rule{4.pt}{0ex}}\text{K})\ensuremath{\sim}0.8$ kOe. Our results, interpreted using different models for thermally activated and surface relaxation processes, can help clarify the complex magnetic behavior of many core/shell and hollow nanoparticle systems.

In order to obtain a complete characterization and understanding of the structural, optical and mechanical properties of LYSO scintillanting crystals, we studied a mechanical, optical and photoelastic model for a cylindrical prism of square cross-section bent by applied loads. This is the starting point which is necessary in order to design a set of mechanical, electrical and optical experiments aimed to obtain the characterization of the macroscopical behavior of LYSO and similar crystals.

The authors analysed the role of diffusion-weighted imaging (DWI) as an additional tool in magnetic resonance (MR) evaluation of prostate cancer.Forty-one patients with suspected prostate cancer underwent MR imaging (1.5 Tesla). A DWI sequence was added to the standard morphological protocol, with a maximum b value of 1,000 s/mm(2). Diffusion maps were obtained, and the apparent diffusion coefficient (ADC) was calculated by drawing a region of interest (ROI) over healthy tissue and areas suspicious for malignancy. Histology was considered the gold standard.The areas correctly classified by MR imaging (42/51) had a low signal intensity on T2-weighted imaging and low ADC value (0.99 ± 0.15 mm(2)/s; p0.01) compared with the healthy peripheral zone (PZ) (1.73 ± 0.27 mm(2)/s; p0.01). Nine areas classified as suspicious for malignancy on T2-weighted sequences showed high ADC (1.44 ± 0.06 mm(2)/s; p0.01) and were confirmed to be disease free by subsequent histological examination. The accuracy of morphofunctional MR imaging was 81.6% compared with 73.7% of the morphological analysis alone.The addition of DWI to the standard protocol increases the overall diagnostic performance of MR imaging in detecting prostatic cancer. Thus, DWI can help the clinician determine the most appropriate management strategy for the patient.

Scintillating crystals are employed in high energy physics, in medical imaging, diagnostic and security. Two mechanical properties of lutetium–yttrium oxyorthosilicate cerium-doped Lu 2(1− x ) Y 2 x SiO 5 :Ce with x =0.1 (LYSO) crystals have been measured: the ultimate tensile stress ( σ UTS ) and the Young elastic modulus ( E ). Measurements are made by means of a 4-points loading device and the experimental results account for an elastic–brittle stress–strain relation, which depends heavily on the specimen preparation and the material defects. σ UTS along the [0 1 0] tensile direction ranges within 68.14 and 115.61 MPa, which, in the lowest case, is more than twice with respect to those measured for PbWO 4 (PWO), exhibiting a marked difference between the annealed and the not-annealed samples. The mean elastic modulus ( E ), along the same direction, is E =1.80×10 11 (±2.15×10 10 ) N/m 2 , with lower dispersion respect to UTS data. This type of analysis and study can be included into quality control procedures of crystals, based on samples taken out of production; such procedures can be established for industrial processing of crystals aimed to the high energy physics (calorimeters) and medical imaging (PET, etc.) applications.

In the field of scintillators, high scintillation and light production performance require high-quality crystals. Although the composition and structure of crystals are fundamental in this direction, their ultimate optical performance is strongly dependent on the surface finishing treatment. This paper compares two surface finishing methods in terms of the final structural condition of the surface and the relative light yield performances. The first polishing method is the conventional &ldquo, Mechanical Diamond Polishing&rdquo, (MDP) technique. The second polishing technique is a method applied in the electronics industry which is envisaged for finishing the surface treatment of scintillator crystals. This method, named &ldquo, Chemical Mechanical Polishing&rdquo, (CMP), is efficient in terms of the cost and material removal rate and is expected to produce low perturbed surface layers, with a possible improvement of the internal reflectivity and, in turn, the light collection efficiency. The two methods have been applied to a lead tungstate PbWO4 (PWO) single crystal due to the wide diffusion of this material in high energy physics (CERN, PANDA project) and diagnostic medical applications. The light yield (LY) values of both the MDP and CMP treated crystals were measured by using the facilities at CERN while their surface structure was investigated by Scanning Electron Microscopy (SEM) and Grazing Incidence X-ray Diffraction (GID). We present here the corresponding optical results and their relationship with the processing conditions and subsurface structure.

Residual internal stresses in PbWO 4 (PWO) scintillating crystals grown by Bridgman method have been systematically studied. Residual stresses induced during growth play an important role in production yield. Cracking probability during mechanical processing as well as stable mechanical properties in finished crystal are closely related to internal stress levels. A regular production of good-quality crystals requires a fast and easy feed-back on growth parameters. Samples from a pre-serial production were analyzed in order to give the producer a quality feed-back for process optimization. By means of photoelasticity, we measured residual stress distribution in several sections along the growth axis and for typical positions in every section. The stress analysis revealed defects occurring during the crystallization process, attributed to dislocations, lattice disorientation and poly-crystallinity. This work had been prompted by the need for quality monitoring of a pre-serial production of PWO for the CMS experiment at CERN's LHC. Mapping stress levels inside the ingot volume and proposing a synthetic parameter to be used as a quality indicator, the resulting analysis should contribute to parameter optimization and improve the growth performance. The proposed method may be useful in conventional crystal production.

In optically birefringent uniaxial and biaxial crystals, analyzed by plane polariscope, isochromate interference fringes can be observed. By means of the classical electromagnetic theory a Cassini-like analytical equation of the isochromate fringes, depending on the refraction indexes, has been obtained. The proposed analytical equation is a useful tool to evaluate the internal stress state, as it is related to the isochromate shapes owing to the induced variation of the refraction indexes. Uniaxial crystals can assume complex biaxial behaviour due to particular stress configurations. PbWO 4 (PWO) uniaxial scintillating crystals have been studied. The Cassini-like curves fit well experimental measurements in the case of uniaxial stress. In this research work, a simple model has been proved in the case of strong isochromate fringes distortion due to a stress gradient induced by the bending load. The model fits well the interference pattern, acquired experimentally. This study can pave the way for the quality control on scintillating crystals, used in the fields of high-energy detectors, security and biomedical applications, with complex internal stress state.

We systematically measured the photo-elastic parameter f σ of PbWO 4 (PWO) for crystals of different thicknesses. We observed a linear behaviour of f σ as a function of the thickness for low level applied stresses. This result was corroborated by numerical simulations. f σ allows the evaluation of the residual internal stress, useful for crystal quality control. In this work, we also propose a new polariscope based on laser light, which allows a fast measurement and mapping of the internal stress of crystals with high resolution owing to the reduced laser-beam dimension.

The assessment of the stress state of scintillating crystals is an important issue for producers as well as users of such materials, because residual stress may arise during growth process. In this paper, a measurement system, based on the use of a photoelastic, conoscopic optical setup, is proposed for the assessment of stress state in scintillating crystals. Local stress values can be measured on the crystal in order to observe their spatial distribution. With the proposed system, it is possible to vary the dimensions of the inspected measurement volume. It has been validated with reference to a known stress state induced in a birefringent crystal sample and it has been tested for the case of loaded and unloaded samples, showing sub-millimetric spatial resolution and stress uncertainty ≤0.25 MPa. The proposed measurement system is a valid method for the inspection of scintillating crystals required by producers and users of such materials.

We report the magnetic and transport properties of the cobalt layered mixed-oxides La1−xSr1+xCoO4 ( 0 ⩽ x ⩽ 0.40 ) . An evolution towards an anomalous “cluster-glass”-like behavior as x increases has been found. The onset of the ferromagnetic order in the layered phases occurs at around 150 K followed by a blocking process around 125 K. Also, present in the magnetic response of these materials is the signal coming from small intergrowths of a perovskite phase, also detected by TEM, although invisible for powder-X-ray diffraction. From the electrical point of view these materials are semiconducting and their resistivity decreases upon doping. Most interestingly, at low temperature these layered compounds show rather large magnetoresistance (MR). The highest effect is found in the sample with x = 0.20 that shows a magnetoresistance MR max = − 24 % at T = 15 K under a field H max = 50 kOe .

The linear and non-linear AC magnetic susceptibilities of the perovskite La1−xSrxCoO3, with 0.15 ⩽ x ⩽ 0.30 , are presented. It is observed that, for x 0.20 , a freezing temperature is defined by AC magnetic susceptibility, pointing to a glassy behaviour whose origin is the phase separation of ferromagnetic metallic-like clusters embedded in an insulating matrix. At this temperature, the non-linear magnetic susceptibility shows critical divergence, similar to spin-glasses, although the width of the diverging peak does not compare well with canonical spin-glasses.

For a reliable mechanical assembly of scintillating crystals for the application to radiographic systems such as Positron Emission Tomographer (PET) and high-energy physics calorimeters (e.g. in CMS at CERN LHC), the evaluation of the monocrystal elastic constant (Young's modulus) is needed. Its knowledge is also essential in the photoelastic analysis for the determination of residual stresses. In this work non-destructive techniques based on elastic wave propagation are tested. They differ in the mechanical excitation device: instrumented hammer, traditional ultrasonic probes and laser-generated ultrasound. We have analysed three non-oriented cerium fluoride crystal samples produced for scintillation applications. Finally, we have validated the experimental results comparing them with the elastic constant calculated by using the stiffness matrix.

Large scintillating crystals are affected by internal stresses induced by the crystal growth temperature gradient remanence. Cutting boules (ingots) into finished crystal shapes allows for a partial tension relaxation but residual stresses remain the main cause of breaking. Quality control of residual stresses is essential in the application of Scintillating Crystals to high-energy physics calorimeters (e.g. CMS ECAL at CERN LHC). In this context the industrial process optimisation towards stress reduction is mandatory. We propose a fast technique for testing samples during the production process in order to evaluate the residual stress distribution after the first phases of mechanical processing. We mapped the stress distribution in PbWO 4 slabs cut from the same production boule. The analysis technique is based on the stress intensity determination using the photo-elastic properties of the samples. The stress distribution is mapped in each sample. The analysis shows that there are regions of high residual tension close to the seed position and at the boule periphery. These results should allow for adapting the industrial process to producing crystals with lower residual stresses.