M. Scaringella

Thermal donors formation via isothermal annealing in magnetic Czochralski high resistivity silicon

A quantitative study about the thermal activation of oxygen related thermal donors in high resistivity p-type magnetic Czochralski silicon has been carried out. Thermal donor formation has been performed through isothermal annealing at 430°C up to a total time of 120min. Space charge density after each annealing step has been measured by transient current technique. The localized energy levels related to thermal double donors (TD) have been observed and studied in details by thermally stimulated currents (TSCs) in the range of 10–70K, and activation energies E and effective cross sections σ have been determined for both the emissions TD0∕+ (E=75±5meV, σ=4×10−14cm2) and TD+∕+ (E=170±5meV, σ=2×10−12cm2). The evolution of the space charge density caused by annealing has been unambiguously related to the activation of TDs by means of current deep level transient spectroscopy TSC, and current transients at constant temperature i(t,T). Our results show that TDs compensate the initial boron doping, eventually pr...

Monte Carlo Studies of a Proton Computed Tomography System

Proton therapy is a precise forms of radiation therapy that makes use of high energy proton compared to the conventional, more commonly used and less precise x-ray and electron beams. On the other hand, to fully exploit the proton therapy advantages, very accurate quality controls of the treatments are required. These are mainly related to the dose calculations and treatment planning. Actually dose calculations are routinely performed on the basis of X-ray computed tomography while a big improvement could be obtained with the direct use of protons as the imaging system. In this work we report the results of Monte Carlo simulations for the study of an imaging system based on the use of high energy protons: the proton computed tomography (pCT). The main limitation of the pCT and the current adopted technical solutions, based on the use of the most likely path (MLP) approximation are illustrated. Simulation results are compared with experimental data obtained with a first prototype of pCT system tested with 200 MeV proton beams available at the Loma Linda University Medical Center (LLUMC) (CA).

Prototype tracking studies for proton CT

As part of a program to investigate the feasibility of proton computed tomography, the most likely path (MLP) of protons inside an absorber was measured in a beam experiment using a silicon strip detector set-up with high position and angular resolution. The locations of 200 MeV protons were measured at three different absorber depth of PolyMethylMethAcrylate-PMMA (3.75, 6.25 and 12.5 cm) and binned in terms of the displacement and the exit angle measured behind the absorber. The observed position distributions were compared to theoretical predictions showing that the location of the protons can be predicted with an accuracy of better than 0.5 mm

A proton Computed Tomography system for medical applications

Proton Computed Tomography (pCT) can improve the accuracy of both patient positioning and dose calculation in proton therapy, enabling to accurately reconstruct the electron density distribution of irradiated tissues. A pCT prototype, equipped with a silicon tracker and a YAG:Ce calorimeter, has been manufactured by an Italian collaboration. First tests under proton beam allowed obtaining good quality tomographic images of a non-homogeneous phantom. Manufacturing of a new large area system with real-time data acquisition is under way.

Architecture of an Ultrasound System for Continuous Real-Time High Frame Rate Imaging

High frame rate (HFR) imaging methods based on the transmission of defocused or plane waves rather than focused beams are increasingly popular. However, the production of HFR images poses severe requirements both in the transmission and the reception sections of ultrasound scanners. In particular, major technical difficulties arise if the images must be continuously produced in real-time, i.e., without any acquisition interruption nor loss of data. This paper presents the implementation of the real-time HFR-compounded imaging application in the ULA-OP 256 research platform. The beamformer sustains an average output sample rate of 470 MSPS. This allows continuously producing coherently compounded images, each of 64 lines by 1280 depths (here corresponding to 15.7 mm width and 45 mm depth, respectively), at frame rates up to 5.3 kHz. Imaging tests addressed to evaluate the achievable speed and quality performance were conducted on phantom. Results obtained by real-time compounding frames obtained with different numbers of steering angles between +7.5° and −7.5° are presented.

A proton Computed Tomography based medical imaging system

This paper reports on the activity of the INFN PRIMA/RDH collaboration in the development of proton Computed Tomography (pCT) systems based on single proton tracking and residual energy measurement. The systems are made of a silicon microstrip tracker and a YAG:Ce crystal calorimeter to measure single protons trajectory and residual energy, respectively. A first prototype of pCT scanner, with an active area of about 5 × 5 cm2 and a data rate capability of 10 kHz, has been constructed and characterized with 62 MeV protons at INFN Laboratori Nazionali del Sud in Catania (Italy) and with 180 MeV protons at The Svedberg Laboratory (TSL) in Uppsala (Sweden). Results of these measurements, including tomographic reconstructions of test phantoms, will be shown and discussed. An upgraded system with an extended field of view (up to ~ 5 × 20 cm2) and an increased event rate capability up to one MHz, presently under development, will be also described.

Tomographic images by proton Computed Tomography system for proton therapy applications

Proton therapy is a highly precise form of cancer treatment, which requires accurate knowledge of the dose delivered to the patient and verification of the correct patient position to avoid damage to critical normal tissues. The development of pCT (proton Computed Tomography) system represents an important feature for precise proton radiation treatment planning because it could permit the direct measurement of the proton stopping power distribution, improving the accuracy in dose calculus, and the patients position. A pCT prototype was manufactured in order to demonstrate the capability to acquire, during treatments in proton therapy centers, radiographic and tomographic images according to clinical demands.

Proton Radiography Studies for Proton CT

We report the results of a beam experiment to develop proton computed tomography (pCT). The set-up consists of telescopes of silicon strip detectors at the entrance and exit of a phantom to predict the path of the proton within the phantom and of a crystal calorimeter to measure the proton energy loss with high precision. The energy loss permits calculating the integrated proton stopping power along each proton path from which the electron density distribution can be reconstructed. We describe the 2D-image reconstruction of a low-contrast phantom, derive the relationship between contrast, pixel size, and dose, and study the spatial resolution achievable with this set-up.

Deep levels in CVD diamond and their influence on the electronic properties of diamond-based radiation sensors

Deep levels in undoped chemical vapor deposited (CVD) diamond films have been characterized by thermally stimulated current spectroscopy (TSC) in the range of 300-650 K. The TSC results have been tentatively correlated tothe performance of the samples as on-line dosimeters and particle detectors. The TSC signal is dominated by a set of deep levels with an activation energy in the range of 1.0-1.4 eV. The trapping activity of these levels, which can be related to grain boundaries, strongly influences the detector performance at room temperature. After neutron irradiation up to the fluence of 2 x 10 1 5 n/cm 2 the amplitude of the TSC signal decreases of about one order of magnitude, the pumping effect becomes significantly less pronounced and the charge collection efficiency decreases of about 30%. Thus, the radiation-induced removal of these deep levels must be accompanied by the creation of other traps, probably vacancy-related and not visible by TSC in this temperature range, which have little effect on the dynamic response of the device but can affect the charge collection efficiency.

Design and characterisation of a YAG(Ce) calorimeter for proton Computed Tomography application

The design and the characterization of a calorimeter system, aimed at measuring the residual energy in a proton Computed Tomography (pCT) apparatus, is described. The calorimeter has a 6 × 6 cm2 active area to fully cover the tracker area of the pCT system, being 10 cm thick it is able to stop up to 200 MeV protons and sustain 1 MHz particle rate (average rate on the whole area). The YAG(Ce) scintillator is promising for charged particle detection applications where high-count rate, good energy resolution and compact photodiode readout, not influenced by magnetic fields, are of importance. The aim of this work is to show data acquired with proton beam energy up to 175 MeV and to discuss the performances of this calorimeter.