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A novel approach for the monitoring of ion beam: where we are

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A novel approach for the monitoring of ion beams: where we are

S.Giordanengo , O. Hammad Ali1 1,2, N. Cartiglia1, F. Fausti1, F. Mas Milian2,3, V. Monaco1,2, R. Sacchi1,2,

Z. Shakarami1,2, A. Vignati1, R. Cirio1,2

1INFN Division of Torino, Via Giuria 1, Torino, Italy; 2Università degli Studi di Torino, Physics Department, Via Giuria 1, Torino, Italy;3Universidade Estadual de Santa Cruz, Ilheus, Brazil

Present online ion beam monitoring systems for particle therapy are based on gas ionization chambers as they offer reliable operation, with limited maintenance. Together with their positive aspects, ionization chambers also feature severe limitations in sensitivity and speed, and therefore cannot support very fast and low dose delivery strategies with the required accuracy.

INFN and University of Torino are working on a novel approach to the beam monitoring, moving from integrating the current in the gas volume of the chamber to counting in real-time every single particle

delivered to the patient. To that aim, the development of two small (3x3 cm2) prototypes of beam monitors

based on Ultra Fast Silicon Detector (UFSD) [1] technology is ongoing to provide two detectors able to measure online the number of particles and the energy of the beam’s particles respectively [2]. Recent and promising results achieved within the “MoVeIT- Modeling and Verification for Ion beam Treatment planning” INFN project will be presented. In detail, we will show:

 The possibility to count individual protons up to 108 p/cm2s, using detectors segmented in strips of 2

mm2 area each and with active thickness of 50 um. Prototype strip sensors have been produced in two

geometries (30 mm and 15 mm length). Different doping modalities were tested for radiation hardness optimization. Beam test characterization and signal pileup inefficiencies will also be shown.

 A dedicated VLSI readout chip (named ABACUS) has been designed and produced to deal with a single proton signal of nanosecond duration and

with 108 Hz signal rate on each channel.

The ABACUS characterization and on beam preliminary performances in reading out UFSD strips will be presented.

 The second device under construction measures protons’ time-of-flight (TOF) between two UFSDs in a telescope configuration (Figure 2), using the

constant fraction algorithm to compensate for time-walk effects. From measured TOF values, the corresponding beam energies are obtained through an analytical approximation validated with Geant4. Following preliminary tests with UFSD pads, dedicated strip sensors

were produced and thinned to 100 um, covering an area of

4x4 mm2. Combinatorial methods to identify coincidences among

strips are being studied.

The work presented has been performed in collaboration with the

UFSD research group of INFN-Torino who is leading the five-years UFSD European ERC Advanced project and will lead the Italian 4DInSiDe: Innovative Silicon Detectors for particle tracking in 4Dimensions project in the next three years. Both these projects are based on Low Gain Avalanche Detector (LGAD) technology: the ERC is studying the characteristics of several possible sensor flavours while 4DInSiDe will use LGAD optimized to develop new particle detectors able to concurrently deliver excellent time and position resolution with high efficiency, at a high rate and in harsh radiation environments. We are partner of the 4DInSide collaboration with the task of designing new detectors for the monitoring of therapeutic ion beams.

[1] Sadrozinski H, Seiden A and Cartiglia N. 4-Dimensional tracking with Ultra-Fast Silicon Detectors.

Reports on Progress in Physics (2018) 81, 026101

Figure 2. Two UFSD strips arranged in a telescope for beam energy measurement.

Figure 1. Strip detector wired-bonded to the ABACUS readout chip.

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[2] A. Vignati et al. “Innovative thin Silicon detectors for monitoring of therapeutic proton beams: preliminary beam tests” JINST 12 C12056

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