Study of coherent interactions between charged particle beams and crystals for beam steering and intense electromagnetic radiation generation

The work presented in this thesis has been devoted to the investigation of new schemes for beam steering and high-intense electromagnetic radiation generation through coherent interactions of charged particle beams with crystals. A series of experiments was carried out in two different laboratories, i.e., the Super Proton Synchrotron (SPS) at CERN in Geneve and the MAinzer MIkrotron (MAMI) of the University of Mainz in Germany, by different international and national collaborations, namely the UA9 experiment., the European CUTE project and the INFN COHERENT and ICE-RAD experiments. The experimental data have been analysed and critically compared with simulations. First of all, the possibility of combining the efficient deflection and the intense electromagnetic radiation production of ultrarelativistic electrons through channeling or volume reflection in bent silicon crystals was investigated. Interesting results were obtained in a wide range of beam energies, spanning from 0.855 GeV available at MAMI to hundreds of GeV accessible at the H4 extracted beamline of SPS. It has been demonstrated the possibility to use bent crystals for efficient deflection of electron beams in the subGeV energy range. This range of energies was still unexplored due to the lack of properly sized bent crystal for negative beams steering. Secondly, it has been shown that the radiation accompanying single (VR) and multiple (MVROC) volume reflection in a bent crystal has peculiar characteristics, such as higher intensity than for bremsstrahlung in an amorphous material and a wide angular acceptance, that make this kind of radiation quite interesting for applications. On the very high-energy side, crystal-aided collimation through radiation accompanying VR and MVROC has been proposed for the future electronpositron colliders, e.g., the International Linear Collider. On the other hand, in the subGeVGeV energy range, which is accessible by most electron accelerators worldwide, the radiation accompanying VR can be exploited as an high-intensity X- or γ-sourse with poor emittance beams. In addition to the studies carried out with electrons, the investigation of new schemes for manipulation of charged beams trajectories was carried out at the H8 beamline of SPS with the usage of 400 GeV/c protons. Firstly, a periodically bent crystal was realized via the superficial grooving method and tested at the H8 line. The effectiveness of this method in achieving perfectly periodic structures was demonstrated. On the strength of these results, it has been proposed to test the crystal sample as a positron-based crystalline undulator in the energy range of 10-20 GeV, as a source of intense MeV photons. Finally, it has been experimentally demonstrated that even a straight crystal, i.e., a crystal mirror, may be used for the steering of ultrarelativistic protons in place of a bent crystal. Unlike the traditional scheme relying on mm-long curved crystals, particle mirroring enables beam steering in high-energy accelerators via interactions with μm-thin straight crystal. The main advantage of mirroring is the interaction with a minimal amount of material along the beam, thereby decreasing unwanted nuclear interactions. Summarizing, all the experimental studies presented in this thesis lead us to consider crystals, either bent or unbent, as reliable tools in particle accelerator physics for different applications within a wide energy range

Steering efficiency of a ultrarelativistic proton beam in a thin bent crystal

Crystals with small thickness along the beam exhibit top performance for steering particle beams through planar channeling. For such crystals, the effect of nuclear dechanneling plays an important role because it affects their efficiency. We addressed the problem through experimental work carried out with 400 GeV/c protons at fixed-target facilities of CERN-SPS. The dependence of efficiency vs. curvature radius has been investigated and compared favourably to the results of modeling. A realistic estimate of the performance of a crystal designed for LHC energy including nuclear dechanneling has been achieved.Comment: 16 pages, 6 figure

Relaxation of axially confined 400 GeV/c protons to planar channeling in a bent crystal

An investigation on the mechanism of relaxation of axially confined 400 GeV/c protons to planar channeling in a bent crystal was carried out at the extracted line H8 from CERN Super Proton Synchrotron. The experimental results were critically compared to computer simulations, showing a good agreement. We identified a necessary condition for the exploitation of axial confinement or its relaxation for particle beam manipulation in high-energy accelerators. We introduce the idea of using a short bent crystal, aligned with one of its main axis to the beam direction, as a beam steerer or a beam splitter with adjustable intensity in the field of particle accelerators. In particular, in the latter case, a complete relaxation from axial confinement to planar channeling takes place, resulting in beam splitting into the two strongest skew planar channels.An investigation on the mechanism of relaxation of axially confined 400 GeV/c protons to planar channeling in a bent crystal was carried out at the extracted line H8 from CERN Super Proton Synchrotron. The experimental results were critically compared to computer simulations, showing a good agreement. We identified a necessary condition for the exploitation of axial confinement or its relaxation for particle beam manipulation in high-energy accelerators. We introduce the idea of using a short bent crystal, aligned with one of its main axis to the beam direction, as a beam steerer or a beam splitter with adjustable intensity in the field of particle accelerators. In particular, in the latter case, a complete relaxation from axial confinement to planar channeling takes place, resulting in beam splitting into the two strongest skew planar channels

Identification of stably expressed reference small non-coding RNAs for microRNA quantification in high-grade serous ovarian carcinoma tissues

MicroRNAs (miRNAs) belong to a family of small non‐coding RNAs (sncRNAs) playing important roles in human carcinogenesis. Multiple investigations reported miRNAs aberrantly expressed in several cancers, including high‐grade serous ovarian carcinoma (HGS‐OvCa). Quantitative PCR is widely used in studies investigating miRNA expression and the identification of reliable endogenous controls is crucial for proper data normalization. In this study, we aimed to experimentally identify the most stable reference sncRNAs for normalization of miRNA qPCR expression data in HGS‐OvCa. Eleven putative reference sncRNAs for normalization (U6, SNORD48, miR‐92a‐3p, let‐7a‐5p, SNORD61, SNORD72, SNORD68, miR‐103a‐3p, miR‐423‐3p, miR‐191‐5p, miR‐16‐5p) were analysed on a total of 75 HGS‐OvCa and 30 normal tissues, using a highly specific qPCR. Both the normal tissues considered to initiate HGS‐OvCa malignant transformation, namely ovary and fallopian tube epithelia, were included in our study. Stability of candidate endogenous controls was evaluated using an equivalence test and validated by geNorm and NormFinder algorithms. Combining results from the three different statistical approaches, SNORD48 emerged as stably and equivalently expressed between malignant and normal tissues. Among malignant samples, considering groups based on residual tumour, miR‐191‐5p was identified as the most equivalent sncRNA. On the basis of our results, we support the use of SNORD48 as best reference sncRNA for relative quantification in miRNA expression studies between HGS‐OvCa and normal controls, including the first time both the normal tissues supposed to be HGS‐OvCa progenitors. In addition, we recommend miR‐191‐5p as best reference sncRNA in miRNA expression studies with prognostic intent on HGS‐OvCa tissues

Enhancement of the Inelastic Nuclear Interaction Rate in Crystals via Antichanneling

The interaction rate of a charged particle beam with the atomic nuclei of a target varies significantly if the target has a crystalline structure. In particular, under specific orientations of the target with respect to the incident beam, the probability of inelastic interaction with nuclei can be enhanced with respect to the unaligned case. This effect, which can be named antichanneling, can be advantageously used in the cases where the interaction between beam and target has to be maximized. Here we propose to use antichanneling to increase the radioisotope production yield via cyclotron. A dedicated set of experimental measurements was carried out at the INFN Legnaro Laboratories with the AN2000 and CN accelerators to prove the existence of the antichanneling effect. The variation of the interaction yield at hundreds of keV to MeV energies was observed by means of sapphire and indium phosphide crystals, achieving an enhancement of the interaction rate up to 73% and 25%, respectively. Such a result may pave the way to the development of a novel type of nozzle for the existing cyclotrons, which can exploit crystalline materials as targets for radioisotope production, especially to enhance the production rate for expensive prime materials with minor upgrades of the current instrumentation

Self-Assembly of Homo- and Hetero-Chiral Cyclodipeptides into Supramolecular Polymers towards Antimicrobial Gels

There is an increasing interest towards the development of new antimicrobial coatings, especially in light of the emergence of antimicrobial resistance (AMR) towards common antibiotics. Cyclodipeptides (CDPs) or diketopiperazines (DKPs) are attractive candidates for their ability to self-assemble into supramolecular polymers and yield gel coatings that do not persist in the environment. In this work, we compare the antimicrobial cyclo(Leu-Phe) with its heterochiral analogs cyclo(D-Leu-L-Phe) and cyclo(L-Leu-D-Phe), as well as cyclo(L-Phe-D-Phe), for their ability to gel. The compounds were synthesized, purified by HPLC, and characterized by 1H-NMR, 13C-NMR, and ESI-MS. Single-crystal X-ray diffraction (XRD) revealed details of the intermolecular interactions within the supramolecular polymers. The DKPs were then tested for their cytocompatibility on fibroblast cells and for their antimicrobial activity on S. aureus. Overall, DKPs displayed good cytocompatibility and very mild antimicrobial activity, which requires improvement towards applications

Geant4 simulation model of electromagnetic processes in oriented crystals for the accelerator physics

Electromagnetic processes of charged particles interaction with oriented crystals provide a wide variety of innovative applications such as beam steering, crystal-based extraction/collimation of leptons and hadrons in an accelerator, a fixed-target experiment on magnetic and electric dipole moment measurement, X-ray and gamma radiation source for radiotherapy and nuclear physics and a positron source for lepton and muon colliders, a compact crystalline calorimeter as well as plasma acceleration in the crystal media. One of the main challenges is to develop an up-to-date, universal and fast simulation tool to simulate these applications. We present a new simulation model of electromagnetic processes in oriented crystals implemented into Geant4, which is a toolkit for the simulation of the passage of particles through matter. We validate the model with the experimental data as well as discuss the advantages and perspectives of this model for the applications of oriented crystals mentioned above.Comment: 18 pages, 9 figure

Medical student perceptions of near peer teaching within an histology course at the University of Sassari, Italy

Near peer teaching (NPT) is becoming recognized as a valuable instrument with advantages for both students and teachers. Despite the recognized benefits, NPT programmes are not usually embedded within university healthcare curricula and, to our knowledge, there have been few studies assessing medical students’ attitudes towards NPT for histology courses. Our study is the first that assess medical students’ perceptions concerning the value of NPT for a course in the human organ histology component of anatomy. A NPT programme was provided for second-year medical students and delivered during laboratory sessions for microscopic anatomy. The NPT tutors were recruited from third-, fourth- or fifth-year medical students. The medical tutees completed a questionnaire to assess their attitudes towards NPT. The initial hypothesis tested was that students preferred to be taught by their professional teachers and not by NPT tutors. A total of 113 students completed the questionnaire (46% response rate). Of these, 70% of respondents rated the support of the NPT tutors as being excellent or good. Furthermore, 60% of respondents agreed that the NPT programme should be introduced officially into the medical curriculum. The findings are not consistent with our initial hypothesis, and suggest that NPT could be a valuable instrument for the understanding of histological concepts