Riccardo Camattari

Bent crystals can be used to deflect high-energy charged particles for beam extraction and/or beam collimation at accelerator facilities, thanks to the channelling phenomenon. In the present paper, two perfect silicon mono-crystals were bent using two different methods: sandblasting and the application of a carbon fibre composite. In particular, these samples were obtained for the realization of bent crystal prototypes to be used to steer the 7 TeV proton beam of the Large Hadron Collider in the context of the CRYSBEAM project. The two bending methods were selected since they allow a very homogeneous curvature of the crystals to be obtained, which is essential for high channelling efficiency. Moreover, the deformation obtained is self-standing, i.e. there is no need for any external device to keep the samples bent. Self-standing curvature can be useful because the presence of an external bender could be a severe limitation in the collider beam-pipe. The curvature of the samples was measured through high-energy X-ray diffraction at the ID11 beamline of the European Synchrotron Radiation Facility in Grenoble, France. Since the diffraction efficiencies obtained were in good agreement with theoretical expectations, it follows that the manufacturing techniques did not damage the samples, i.e. the crystallographic quality was preserved. Finally, the crystal quality of the sandblasted sample was investigated in detail at the synchrotron source at Karlsruhe Institute of Technology by X-ray white-beam topography. The measurements showed no diffusion of defects from the machined surfaces to the crystal bulk.

The production techniques of radioisotopes for medical purposes is a valuable and important field in nuclear medicine. In particular, the expensive cost of the prime materials for the production via cyclotron obliges the search for new solutions to enhance the production rate with minor upgrades of the current instrumentation. Oriented ordered structure can modify particle trajectories inside a medium leading to a sensible variation of the interaction rate with atomic nuclei. 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 standard rate. This effect is called anti-channeling and leads to an increase of the radioisotope production yield. A dedicated set of experimental measurements were carried out at the CN accelerator of the INFN Legnaro Laboratories to investigate nuclear reactions under channeling experiments. In particular, the production of the Arsenic-74 radioisotope through a proton beam delivered to a natural single-crystal Germanium target was monitored via γ-spectroscopy of the prompt γ-rays upon de-excitation of produced nuclei, in order to quantify the production rate variation as a function of the incident angle.

Since the ’70, physics of interaction between bent crystals and heavy particles (protons or ions)

Since their discovery, scintillator materials have played an important role in nuclear and particle physics, as well as in medical and industrial imaging.

High purity germanium (HPGe) is the key material for gamma ray detectors production. Its high purity level (⩽2 · 10 ⁻⁴ ppb of doping impurity) has to be preserved in the bulk during the processes needed to form the detector junctions. With the goal of improving the device performance and expanding the application fields, in this paper many alternative doping processes are evaluated, in order to verify their effect on the purity of the material. In more detail, we investigated the electrical activation of contaminating doping defects or impurities inside the bulk HPGe, induced by both conventional and non-conventional surface doping processes, such as boron ion implantation, phosphorus and gallium diffusion from spin-on doping sources, antimony equilibrium diffusion from a remote sputtered source and laser thermal annealing (LTA) of sputtered antimony. Doping defects, thermally-activated during high temperature annealing, were characterized through electrical measurements. A phenomenological model describing the contamination process was developed and used to analyze the diffusion parameters and possible process thermal windows. It resulted that out-of-equilibrium doping processes confined to the HPGe surface have higher possibilities to be successfully employed for the formation of thin contacts, maintaining the pristine purity of the bulk material. Among them, LTA turned out to be the most promising.

Focusing a hard x-ray beam would represent an innovative technique for tumour treatment, since such a beam may deliver a dose to a tumour located at a given depth under the skin, sparing the surrounding healthy cells. A detailed study of a focusing system for hard x-ray aimed at radiotherapy is presented here. Such a focusing system, named Laue lens, exploits x-ray diffraction and consists of a series of crystals disposed as concentric rings capable of concentrating a flux of x-rays towards a focusing point. A feasibility study regarding the positioning tolerances of the crystalline optical elements has been carried out. It is shown that a Laue lens can effectively be used in the context of radiotherapy for tumour treatments provided that the mounting errors are below certain values, which are reachable in the modern micromechanics. An extended survey based on an analytical approach and on simulations is presented for precisely estimating all the contributions of each mounting error, analysing their effect on the focal spot of the Laue lens. Finally, a simulation for evaluating the released dose in a water phantom is shown.