arXiv subjects

Matthias Knopf

Publications and source records attributed to Matthias Knopf.

10 recordsLinked to original sources

arXiv2026

Spectacular - A Modular DAQ System for Microdosimetry

Particle therapy using light ions like protons, helium ions or carbon ions enables precise tumor targeting with enhanced biological effectiveness while minimizing damage to healthy tissue. Successful treatment planning depends not only on the absorbed dose but also on quality of the radiation, as quantified by the linear energy transfer (LET). Microdosimetry provides a direct experimental determination of such quantities by measuring the energy deposited per incoming particle in micrometer-sized solid-state detectors representing the relevant biological scales. However, the small signal amplitudes and high particle rates in therapeutic ion beams challenge existing readout systems, which are not sufficiently optimized for reliable operation with respect to pileup and signal-to-noise ratio (SNR). To address this, a modular data acquisition (DAQ) system was developed to accelerate the design of custom readout electronics and sensor characterization in microdosimetry and related spectroscopic applications. Centered around a Xilinx Zynq system-on-chip, it combines real-time processing, high-bandwidth streaming, and high-resolution digitization (16 bit at 100 MSas$^{-1}$) to enable advanced digital signal processing. The platform integrates programmable power supplies, a bias-voltage filter, test-pulse generators, and flexible I/O. Detector and preamplifier front-ends are hosted on interchangeable daugtherboards connected via a standardized interface, allowing different hardware configurations and readout algorithms to be evaluated on the same platform. The Spectacular DAQ system was successfully tested at the MedAustron ion therapy facility with custom charge-sensitive amplifiers and a diamond microdosimeter. First results demonstrate the feasibility and provide a proof-of-concept for potential future applications in clinical practice.

physics.ins-det↗

arXiv2026

A frontend ASIC for Microdosimetry

Recent clinical evidence shows a correlation between linear energy transfer (LET) and tumor control in carbon ion radiotherapy. This prompts the direct inclusion of LET into the treatment planning. Currently, LET is mainly extracted from simulations. Good clinical practice requires adopting measurement routines that correlate with LET, such as microdosimetry. In this work, we describe an application-specific integrated circuit (ASIC) for reading out microdosimeteric sensors. The ASIC is designed for input capacitances up to 3 pF. It contains four readout channels, each with a different saturation charge ranging from 75 fC to 3.2 pC. In the 75 fC range, at 1 pF input capacitance and a shaping time of 1 microseconds, the ASIC has an equivalent noise contribution (ENC) below 15 electrons at ambient temperature. This low noise level is expected to enable new measurement possibilities, including the assessment of microdosimetric proton spectra in the low-LET region of the entrance channel, as well as studying the contribution of delta electrons.

hep-ex↗

arXiv2026

Measurements of the micro-spill structure of medical cyclotron and synchrotron beams and its impact on pulse pileup

Detector characterization and instrumentation testing are often performed at cyclotron and synchrotron facilities, many of which were originally developed for medical applications in cancer therapy. For particle physics experiments requiring a single-particle resolution, pileup can significantly degrade data quality, making precise knowledge of the beam time structure essential for selecting appropriate readout parameters. However, such information is often unavailable from the facilities and challenging to determine experimentally. Here, we report measurements of the spill time structure at two medical accelerator facilities using a silicon carbide (SiC) particle sensor coupled to a high-frequency readout system. Owing to its high carrier saturation velocity and the tolerance to large bias voltages, SiC is well suited for fast readout and measurements requiring precise timing. Using a 6 GHz readout with custom SiC diodes, we characterize the micro-spill structure of both cyclotron and synchrotron beams on a sub-nanosecond timescale. The measured arrival-time distributions exhibit modulation with the accelerator RF frequencies, reflecting features of the extraction process. The resolved micro-spill structure enables quantitative estimation of pileup contributions and provides design constraints for future readout electronics. The presented results emphasize the importance of the characterization of the beam time-structure characterization for the development of precise readout systems.

physics.ins-det↗

arXiv2025

Design and simulation of a 4H-SiC low gain avalanche diode with trench-isolation

We present the design and simulation of a 30 $\mathrm{\mu m}$ thick 4H-SiC Low Gain Avalanche Diode (LGAD) optimized for high-voltage operation. A 2.4 $\mathrm{\mu m}$ thick epitaxially grown gain layer enables controlled internal amplification up to 1 kV reverse bias, while maintaining full depletion below 500 V. Electrical characteristics, including I-V, C-V, and gain behavior, were simulated in Synopsys Sentaurus Technology Computer-Aided Design (TCAD) using a quasi-1D geometry and verified across process-related variations in gain layer parameters. To ensure high-voltage stability and proper edge termination, a guard structure combining deep etched trenches and deep $p^+$ junction termination extension (JTE) implants was designed. TCAD simulations varying the guard structure dimensions yielded an optimized design with a breakdown voltage above 2.4 kV. A corresponding wafer run is currently processed at IMB-CNM, Barcelona.

physics.ins-det↗

arXiv2025

In-situ Radiation Damage Study of Silicon Carbide Detectors Subjected to Clinical Proton Beams

Silicon carbide (SiC) planar PiN diodes from two different manufacturers were irradiated with 252.7 MeV protons from a medical synchrotron. Over the course of two 8h irradiation shifts, the samples were exposed to increasing fluences ranging from 1.4e+11 to 3.5e+13 p+/cm^2. Electrical characterizations, including IV and CV measurements, were performed both before and after irradiation using probe stations, and for selected samples even in-situ between fluence steps directly at the irradiation facility. The results show a gradual compensation of the effective epitaxial doping concentration with each incremental fluence step, observed as a reduction in capacitance before full depletion and confirmed by the extracted effective doping concentration. From these measurements, linear donor removal rates are determined for all sample groups, with values ranging from 4.2/cm to 6.4/cm. These findings provide a quantitative basis for understanding radiation-induced charge carrier removal in 4H-SiC devices and are relevant for predicting the performance and lifetime of future radiation-hard detector technologies, including 4H-SiC LGADs.

physics.ins-det↗

arXiv2025

Extraction of Electron and Hole Drift Velocities in thin 4H-SiC PIN Detectors using High-Frequency Readout Electronics

Silicon carbide (SiC) has been widely adopted in the semiconductor industry, particularly in power electronics, because of its high temperature stability, high breakdown field, and fast switching speeds. Its wide band gap makes it an interesting candidate for radiation-hard particle detectors in high-energy physics and medical applications. Furthermore, the high electron and hole drift velocities in 4H-SiC enable devices suitable for ultra-fast particle detection and timing applications. However, currently, the front-end readout electronics used for 4H-SiC detectors constitute a bottleneck in investigations of the charge carrier drift. To address these limitations, a high-frequency readout board with an intrinsic bandwidth of 10 GHz was developed. With this readout, the transient current signals of a 4H-SiC diode with a diameter of 141 $\mathrm{\mu m}$ and a thickness of 50 $\mathrm{\mu m}$ upon UV-laser, alpha particle, and high-energy proton beam excitation were recorded. In all three cases, the electron and hole drift can clearly be separated, which enables the extraction of the charge carrier drift velocities as a function of the electric field. These velocities, for the first time directly measured, provide a valuable comparison to Monte-Carlo simulated literature values and constitute an essential input for TCAD simulations. Finally, a complete simulation environment combining TCAD, the Allpix$^2$ framework, and SPICE simulations is presented, in good agreement with the measured data.

physics.ins-det↗

arXiv2025

Characterizing the Delivered Spill Structure of Medical Proton and Carbon-Ion Beams at MedAustron using a High Frequency Silicon Carbide Readout

Medical synchrotrons are often used for testing instrumentation in high-energy physics or non-clinical research in medical physics. In many applications of medical synchrotrons, such as microdosimetry and ion imaging, precise knowledge of the spill structure and instantaneous particle rate is crucial. Conventional ionization chambers, while omnipresent in clinical settings, suffer from limitations in charge resolution and integration time, making single-particle detection at high dose rates unfeasible. To address these limitations, we present a beam detection setup based on a silicon carbide (SiC) sensor and a monolithic microwave integrated circuit (MMIC), capable of detecting single particles with a full width at half maximum (FWHM) pulse duration of 500 ps. At the MedAustron ion therapy center, we characterized the spill structure of proton and carbon-ion beams delivered to the irradiation room beyond the timescale of the maximum ion revolution frequency in the synchrotron. The resulting data offer valuable insights into the beam intensity at small time scales and demonstrate the capabilities of SiC-based systems for high-flux beam monitoring.

physics.ins-det↗

arXiv2025

From Single Particles to Clinical Beam Rates: A Wide Dynamic Range Beam Monitor

Access to high-energy particle beams is key for testing high-energy physics (HEP) instruments. Accelerators for cancer treatment can serve as such a testing ground. However, HEP instrument tests typically require particle fluxes significantly lower than for cancer treatment. Thus, facilities need adaptations to fulfill both the requirements for cancer treatment and the requirements for HEP instrument testing. We report on the progress made in developing a beam monitor with a sufficient dynamic range to allow for the detection of single particles, while still being able to act as a monitor at the clinical particle rates of the MedAustron treatment facility. The beam monitor is designed for integration into existing accelerators.

physics.acc-ph↗

arXiv2024

Exploring Offline Pileup Correction to Improve the Accuracy of Microdosimetric Characterization in Clinical Ion Beams

Microdosimetry investigates the energy deposition of ionizing radiation at microscopic scales, beyond the assessment capabilities of macroscopic dosimetry. This contributes to an understanding of the biological response in radiobiology, radiation protection and radiotherapy. Microdosimetric pulse height spectra are usually measured using an ionization detector in a pulsed readout mode. This incorporates a charge-sensitive amplifier followed by a shaping network. At high particle rates, the pileup of multiple pulses leads to distortions in the recorded spectra. Especially for gas-based detectors, this is a significant issue, that can be reduced by using solid-state detectors with smaller cross-sectional areas and faster readout speeds. At particle rates typical for ion therapy, however, such devices will also experience pileup. Mitigation techniques often focus on avoiding pileup altogether, while post-processing approaches are rarely investigated. This work explores pileup effects in microdosimetric measurements and presents a stochastic resampling algorithm, allowing for offline simulation and correction of spectra. Initially it was developed for measuring neutron spectra with tissue equivalent proportional counters and is adapted for the use with solid-state microdosimeters in a clinical radiotherapy setting. The algorithm was tested on data acquired with solid-state microdosimeters at the MedAustron ion therapy facility. The successful simulation and reduction of pileup counts is achieved by establishing of a limited number of parameters for a given setup. The presented results illustrate the potential of offline correction methods in situations where a direct pileup-free measurement is currently not practicable.

physics.med-ph↗

arXiv2023

Measurement of the electron-hole pair creation energy in a 4H-SiC p-n diode

For 4H silicon carbide (4H-SiC), the values for the electron-hole pair creation energy $\epsilon_{\text{i}}$ published in the literature vary significantly. This work presents an experimental determination of $\epsilon_{\text{i}}$ using $50$ $\mu$m 4H-SiC p-n diodes designed for particle detection in high-energy physics. The detector response was measured for $\alpha$ particles between 4.2 MeV and 5.6 MeV for 4H-SiC and a silicon reference device. Different $\alpha$ energies were obtained by using multiple nuclides and varying the effective air gap between the $\alpha$ source and the detector. The energy deposited in the detectors was determined using a Monte Carlo simulation, taking into account the device cross-sections. A linear fit of the detector response to the deposited energy yields $\epsilon_{\text{i}} = (7.83 \pm 0.02)\;\text{eV}$, which agrees well with the most recent literature. For the 4H-SiC detectors, a linewidth of 28 keV FWHM was achieved, corresponding to an energy resolution of 0.5\%.

physics.ins-det↗