Advacam (Czechia)

This work summarizes the evaluation results of chromium compensated GaAs sensors manufactured by Advafab and evaluated with different photon counting readout electronics. Recently Advafab has fabricated GaAs diode and pixel sensors on 3” wafers with 1-, 1.5 - and 2-mm thicknesses. Diode measurement results present an analytical evaluation of charge transport properties of different thicknesses of GaAs and their spectral response to Alpha and Gamma radiation. Flip chip bonded pixel sensor assemblies were evaluated to study uniformity; sensor stability; energy resolution; charge transport properties and high X-ray flux operation. The presentation covers pixel sensor performance, properties and differences of the chromiumcompensated GaAs of different thicknesses and their usability in photon counting applications.

Semiconductor hybrid pixel detectors have found applications in many fields like biomedical imaging, material analysis and space weather monitoring. Their ability of particle tracking enables analysis of mixed radiation fields useful around accelerators and fusion or fission reactors. These harsh environments require hard materials. The SiC is very perspective semiconductor material providing high radiation hardness and wide temperature operation. The first hybrid pixel detector with SiC sensor, the SiC-Timepix3 detector, was prepared in 2022 [1]. There, the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$80 \mu ~\mathrm{m}$</tex> thick epitaxial layer of 4 H - (four-hexagonal polytype) SiC on <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$350 \mu ~\mathrm{m}$</tex> thick substrate creates detector sensitive layer. The 4 H-SiC sensor pixelated structure of Schottky electrodes bump-bonded to Timepix3 read-out chip create the depletion regions defining individual detection zones. Their depths increase with reverse biasing of the structure through Timepix3 chip adjusting the active thickness of sensitive epitaxial layer. The capacitance-voltage measurement on single diode detectors from the same 4 H-SiC material have revealed the exact penetration depth of depletion region with applied reverse bias. Half of the layer is depleted with −55 V, for full depletion −220 V is needed. In this paper we examine the detector spectral response to fast neutrons and gamma rays at different detector biasing. The detection efficiency of the 14 MeV neutrons from D-T neutron generator and gamma and X-rays from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }^{241} \text{Am}$</tex> with SiC-Timepix3 detector biased to various reverse voltages was in agreement with responsible active thicknesses calculated from capacitance measurements. Moreover, the ability of Timepix detector to make spectral particle tracking [2] was utilized to filter events corresponding to the neutron interaction with the SiC material.

In this work, an in-situ study of phase transitions in low-carbon steel is presented. The phase changes were monitored by the transmission energy dispersive X-ray diffraction technique during the heating, annealing and quenching cycle of the sample under standard laboratory conditions. During energy dispersive X-ray diffraction, the sample volume was transmitted with a pencil beam generated by a standard polychromatic X-ray tube without any spectral filtering. Two-dimensional polychromatic diffraction images were acquired by a Timepix3 pixelated detector. This detector is capable of achieving a throughput of up to 38Mhits/s in continuous stream mode using USB 3.0 interface. For each detected photon, its position is known with an accuracy of 55µm in the detector plane and its energy with a resolution of 4keV at 60keV. The recorded polychromatic data is then recomputed to get the equivalent monochromatic XRD pattern that would be produced using a monochromatic X-ray source. Thanks to the 90kV voltage potential of the X-ray tube, the polychromatic pencil beam was able to pass through a highly attenuating sample made of 1.5 thick steel sheet. In addition, by utilizing the entire X-ray spectrum, the pencil beam has a sufficiently high brilliance to obtain XRD patterns rapidly enough to investigate relatively fast processes with temporal resolution of 10s. It made to possible to analyze the phase transitions in a polycrystalline sample during its temperature treatment under standard laboratory conditions.

In particle radiotherapy practice it is valuable to examine, accurately measure and monitor the secondary radiation fields produced during treatment. Measurements performed non-invasively and out-of-field avoid interfering with and modifying the delivered dose treatment. Use of a simplified and compact device is advantageous for reduced cost and effort of deployment and operation. For this purpose, we examine in detail the scattered beam particles and secondary radiation field produced well beyond even meters away from the irradiated area in proton therapy. We use the semiconductor pixel detector Timepix3 implemented as a miniaturized radiation camera which we mounted at the ceiling of the treatment room. The pixel detector provides high-resolution per-pixel spectrometry with time, position, directional and tracking response. Applying radiation imaging and particle tracking techniques together with extensive experimental calibrations in well-defined radiation fields, the single detector provides the composition and spectral-tracking characterization of the complex fields. In particular, the scattered proton field at the detector position is evaluated and unfolded into spectral-directional groups which serve to map and examine the characteristics and directional origin of the radiation out of field. Detailed particle fluxes and dose rates, total and partial, are measured out of field with sub-second time resolution. Deposited energy distributions in the detector sensor are derived in wide range. Verification and complementary information are provided by numerical Monte-Carlo (MC) simulations. The combined results and presented technique can be potentially used to inspect and systematically evaluate quality assurance irradiations and treatment plans.

We performed detailed measurements of the secondary cosmic ray field in the lower atmosphere (at 200 m). We use a miniaturised particle telescope consisting of two closely stacked synchronised Timepix3 detectors. Position-, spectral-, and time-sensitive particle tracking provides enhanced particle-type resolving power and high angular resolution mapping of charged particles. Evaluation and calibration of the telescope synchronised tracking and directional response was performed with proton and electron beams. The telescope architecture, modeled angular response and developed data analysis provide accurate composition characterisation and high-angular resolution directional mapping of the charged particle component. In particular, the muon component can be resolved to a high degree over the photon and electron components in the lower atmosphere. The muon angular flux is measured in a wide field of view with enhanced discrimination.

The time structures of proton spot delivery in proton pencil beam scanning (PBS) radiation therapy are essential in many clinical applications. This study aims to characterize the time structures of proton PBS delivered by both synchrotron and synchrocyclotron accelerators using a non-invasive technique based on scattered particle tracking. A pixelated semiconductor detector, AdvaPIX-Timepix3, with a temporal resolution of 1.56ns, was employed to measure time of arrival of secondary particles generated by a proton beam. The detector was placed laterally to the high-flux area of the beam in order to allow for single particle detection and not interfere with the treatment. The detector recorded counts of radiation events, their deposited energy and the timestamp associated with the single events. Individual recorded events and their temporal characteristics were used to analyze beam time structures, including energy layer switch time, magnet switch time, spot switch time, and the scanning speeds in the x and y directions. All the measurements were repeated 30 times on three dates, reducing statistical uncertainty. The uncertainty of the measured energy layer switch times, magnet switch time, and the spot switch time were all within 1% of average values. The scanning speeds uncertainties were within 1.5% and are more precise than previously reported results. The measurements also revealed continuous sub-milliseconds proton spills at a low dose rate for the synchrotron accelerator and radiofrequency pulses at 7µs and 1ms repetition time for the synchrocyclotron accelerator. The AdvaPIX-Timepix3 detector can be used to directly measure and monitor time structures on microseconds scale of the PBS proton beam delivery. This method yielded results with high precision and is completely independent of the machine log files.

Objective. This study aims to assess the composition of scattered particles generated in proton therapy for tumors situated proximal to some titanium (Ti) dental implants. The investigation involves decomposing the mixed field and recording Linear Energy Transfer (LET) spectra to quantify the influence of metallic dental inserts located behind the tumor. Approach. A therapeutic conformal proton beam was used to deliver the treatment plan to an anthropomorphic head phantom with two types of implants inserted in the target volume (made of Ti and plastic, respectively). The scattered radiation resulted during the irradiation was detected by a hybrid semiconductor pixel detector MiniPIX Timepix3 that was placed distal to the Spread-out Bragg peak. Visualization and field decomposition of stray radiation were generated using algorithms trained in particle recognition based on artificial intelligence neural networks (AI NN). Spectral sensitive aspects of the scattered radiation were collected using two angular positions of the detector relative to the beam direction: 0° and 60°. Results. Using AI NN, 3 classes of particles were identified: protons, electrons & photons, and ions & fast neutrons. Placing a Ti implant in the beam’s path resulted in predominantly electrons and photons, contributing 52.2% of the total number of detected particles, whereas for plastic implants, the contribution was 65.4%. Scattered protons comprised 45.5% and 31.9% with and without metal inserts, respectively. The LET spectra were derived for each group of particles identified, with values ranging from 0.01 to 7.5 keV μm−1 for Ti implants/plastic implants. The low-LET component was primarily composed of electrons and photons, while the high-LET component corresponded to protons and ions. Significance. This method, complemented by directional maps, holds the potential for evaluating and validating treatment plans involving stray radiation near organs at risk, offering precise discrimination of the mixed field, and enhancing in this way the LET calculation.

This work summarizes the evaluation results of chromium compensated GaAs sensors manufactured by Advacam Oy and evaluated with four different photon counting readout electronics. Flip chip bonded assemblies were evaluated to study the optimal sensor design and bias voltage; uniformity; sensor stability; energy resolution; Modulation Transfer Function (MTF) and high X-ray flux operation. The presentation summarizes the GaAs performance results received from the contributing authors. It presents analytical comparisons to the other commercially available GaAs sensor material in terms of uniformity and spectral resolution. Advacam's GaAs present better uniformity and similar or better energy resolution. The presentation concludes that it is possible to manufacture radiation sensors of chromium compensated GaAs with high uniformity and a good energy resolution that can operate at high X-ray fluxes.