Publications

Semiconductor hybrid pixel detectors with Timepix 3 chips developed by Medipix collaboration at CERN can simultaneously measure deposited energy and time of arrival of individual particle hits in all 256 × 256 pixels with 55 μm pitch size. Leveraging the single-particle detection sensitivity of these chips, there is a potential to develop algorithms for classifying detected single particles into distinct categories corresponding to different particle types. In this study, various machine learning models are introduced, such as recurrent and feedforward neural networks or gradient boosted decision trees, designed to facilitate the classification of single particle events into distinct classes associated to electrons & photons, alpha particles, heavy nuclei (except alpha particles), low energy protons (E ≲ 100 MeV) and high energy protons (E ≳ 100 MeV). All models achieve outcomes with the true positive rate nearing 100% across all classes. The Gaussian Mixture unsupervised machine learning technique is used to differentiate between electron and photon radiation components. The model effectively distinguished between high-energy electrons and low-energy photons, achieving performance comparable to conventionally used heuristic decision trees. All models are trained and tested on an extensive database of experimental data obtained from controlled radiation source experiments.

Volume: 20
Article Number: C01028
DOI: 10.1088/1748-0221/20/01/C01028

Ion-beam radiotherapy is a growing cancer treatment modality because it offers a superior dose distribution in the patient compared with conventional radiotherapy using X-rays. Thanks to their versatility, application-specific integrated circuits (ASIC) increasingly gain interest for research into ion imaging and ion-beam characterisation. Timepix3 is a hybrid semiconductor pixel detector, which offers nanosecond time binning as well as dead-time-free and noise-free data-driven readout at a pixel pitch of 55 µm × 55 µm. In this work, a novel 4-chip Timepix3 mini-tracker (quad module) was characterised in a therapeutic proton beam. The quad module has two detection layers equipped with two Timepix3 chips each, which are stacked like a particle telescope at a distance of 20.3 mm. In a detection layer, two Timepix3 chips share the same sensitive silicon sensor. The surface area of the silicon sensor is approximately 28 mm × 14 mm. Apart from the pixels at the chip edges and the masked pixels, the quad module showed a uniform counting response to the mono-energetic proton irradiation without noticeable defects. The measurement accuracy of the energy deposition was found to be better than 1 % at 340 keV. The synchronisation between the four chips of the quad module showed systematic delays of up to 25 ns. When these delays are corrected, the time resolution of the quad module is (1.17 ± 0.03) ns. The time resolution could be further improved with the implementation of a time-walk correction. It is concluded that the quad module fulfils the requirements to be used as a charged-particle tracker in ion-beam radiotherapy. Future testing will focus on the radiation hardness, dose-rate dependence and response to high-LET radiation.

Volume: 173
Article Number: 107086
DOI: https://doi.org/10.1016/j.radmeas.2024.107086

The introduction of the new hybrid pixel detector Timepix2, as a successor to the well-known Timepix detector, has presented new opportunities for optimizing and characterizing this novel device. In this paper, we study the Timepix2 detector optimization and analyze its behavior, which enables better parameter setting for specific applications, resulting in enhanced device performance. Our newly developed equalization process, in conjunction with the device optimization, has led to significant improvements in the detector's accuracy and performance, facilitating more precise data collection and analysis. These advancements pave the way for the broader utilization of Timepix2 in numerous applications, such as space weather monitoring, X-ray diffraction, etc. Overall, our study provides valuable insights into the optimization and characterization of Timepix2, highlighting its potential as a powerful tool in various scientific, industrial and space applications.

Volume: 19
Article Number: C01007
DOI: https://doi.org/10.1088/1748-0221/19/01/C01007

Monitoring and characterization of particle beams in wide-range is often necessary in research and many applications with particle accelerators. The quantitative measurement and evaluation of composition especially of high-intensity beams are limited and can become a challenge with conventional methods especially with simplified instrumentation for ease of deployment. For this purpose, we developed a novel technique based on high-resolution spectral-sensitive tracking of single particles scattered from the beam path by a thin foil. We use a compact radiation camera equipped with the semiconductor pixel detector Timepix3 together with dedicated Monte-Carlo simulations. Particle-event type discrimination and directional information are produced by the detector spectral-tracking response together with particle-type resolving power derived from experimental calibrations. Directional- and spectral-sensitive components can be resolved in wide field-of-view. Quantification of the primary beam intensity is extrapolated by numerical calculations. Demonstration and evaluation of the technique are provided by measurements with 33 MeV protons from a light ion cyclotron accelerator. Scattered particles originating from the thin foil, the accelerator beam nozzle, and the air space along the beam path are detected and evaluated.

Volume: 19
Article Number: C02054
DOI: https://doi.org/10.1088/1748-0221/19/02/C02054

A Schottky barrier radiation detector and pixel imaging sensor fabricated from epitaxially grown SiC semiconductor were analyzed. The detector was based on an 80 μm thick epitaxial SiC layer. Capacitance-voltage measurement was performed to study the thickness of the space charge region of the detector as a function of applied bias. The results showed that the detector was completely depleted at a reverse bias higher than 300 V. The impurity concentration profile was also calculated, which indicated a net impurity concentration below 1.5×1014 cm-3. A prototype of a SiC Timpix3 radiation camera was fabricated, and its energy resolution was investigated using the 241Am radioisotope. The camera exhibited an energy resolution of 4.5 keV for 60 keV gamma photons. X-ray fluorescence photons (from 14 keV to 22 keV) were detected with a resolution below 2.0 keV. The imaging quality of the camera was investigated using a test object. The prototype showed a high-quality image performance with a stable count rate, which was determined from uniform intensity profiles extracted from parts of the test object image. A disadvantage of this prototype is that the radiation hits the detector from the side of the substrate and only then it reaches its active SiC epitaxial layer. This represents a dead layer that reduced the detection efficiency of X-rays below 10 keV.

Volume: 19
Article Number: C01003
DOI: https://doi.org/10.1088/1748-0221/19/01/C01003

Mixed-radiation fields in environments such as particle radiotherapy and outer space exhibit large complexity in terms of composition and spectral distribution which are difficult to measure in detail. For this purpose, we present a high-sensitivity technique using the pixel detector Timepix3 to measure the composition and spectral-tracking characterization of secondary fields produced in proton radiotherapy. Particle-event classes are resolved into broad groups of high-energy transfer particles (HETPs), such as protons, ions, and neutrons, as well as low-energy transfer particles (LETPs), such as electrons, X-rays, and, partly, low-energy gamma rays. The quantum-imaging capability of Timepix3 is exploited to enhance the resolving power for particle-type classification. The particle tracks are analyzed by spectral-sensitive pattern recognition algorithms. The response matrix for Timepix3 is newly derived and is based on experimental calibrations in well-defined radiation fields including in-beam rotational scans of protons performed at various energies and directions. Clinical proton beams of radiotherapeutic intensities and energies in the range 225–12 MeV were used in experimental configurations with and without a tissue-equivalent phantom. Detailed results of radiation components can be used to produce total and partial particle fluxes, dose rate, absorbed dose, deposited energy, and linear-energy-transfer (LET) spectra. Dedicated Monte Carlo (MC) simulations are compared with experimental results of field composition, particle fluence, and deposited energy. The numerical information aids the interpretation of experimental data, which includes also secondary neutrons. The technique and developed methodology can be applied for research and routine measurements in environments of varying complexity.

Volume: 71
DOI: https://doi.org/10.1109/TNS.2024.3369972

Hybrid semiconductor pixelated detectors from the Timepix family are advanced detectors for online particle tracking, offering energy measurement and precise time stamping capabilities for particles of various types and energies. This inherent capability makes them highly suitable for various applications, including imaging, medical fields such as radiotherapy and particle therapy, space-based applications aboard satellites and the International Space Station, and industrial applications. The data generated by these detectors is complex, necessitating the development and deployment of various analytical techniques to extract essential information. For this purpose, and to aid the Timepix user community, it was designed and developed the "Data Processing Engine" (DPE) as an advanced tool for data processing designed explicitly for Timepix detectors. The functionality of the DPE is structured into three distinct processing levels: i) Pre-processing: this phase involves clusterization and the application of necessary calibrations and corrections. ii) Processing: this stage includes particle classification, employing machine learning algorithms, and the recognition of radiation fields. iii) Post-processing: involves various analyses, such as directional analysis, coincidence analysis, frame analysis, Compton directional analysis, and the generation of physics products, are performed. The core of the DPE is supported by an extensive experimental database containing calibrations and referential radiation fields of typical environments, including protons, ions, electrons, gamma rays and X rays, as well as thermal and fast neutrons. To enhance accessibility, the DPE is implemented into various user interface platforms such as a command-line tool, an application programming interface, and as a graphical user interface in the form of a web portal. The DPE's broad utility is exemplified through its integration into various applications and developments.

Volume: 19
Article Number: C04026
DOI: https://doi.org/10.1088/1748-0221/19/04/C04026

he TraX Engine is an advanced data processing tool developed by ADVACAM in collaboration with the European Space Agency (ESA), specifically designed for analyzing data from Timepix detectors equipped with various sensor materials (Si, CdTe, GaAs, SiC). TraX Engine can process large datasets across various scientific and medical applications, including space radiation monitoring, particle therapy, and imaging. In space applications, the TraX Engine has been used to process data from satellites like OneWeb JoeySat deployed in LEO orbit, where it continuously monitors space radiation environments measuring flux, dose, and dose rate in real-time. In medical applications, particularly in particle therapy, the TraX Engine is used to process data to characterize radiation fields in terms of particle flux, Linear Energy Transfer, and spatial distribution of the radiation dose. The TraX Engine can identify and classify scattered particles, such as secondary protons and electrons, and estimate their contribution to out-of-field doses. In imaging applications, the TraX Engine is integrated into Compton cameras, where it supports photon source localization through directional reconstruction of photons. The system ability to identify gamma radiation source with high precision makes it suitable for medical imaging tasks, such as tracking I-131 used in thyroid cancer treatment or localizing radiation sources. This paper presents the architecture and capabilities of the newly developed software TraX Engine, alongside results from various applications, demonstrating its role in particle tracking, radiation monitoring, imaging, and others. With its modular architecture, the TraX Engine offers multiple interfaces, including a command-line tool, an API, a web portal, and a graphical user interface, ensuring usability across different fields and user expertise levels.

Volume:
Article Number:
DOI: https://doi.org/10.48550/arXiv.2410.10242

Analysis and characterization of 2D and 3D objects is widely used forensics and materials research. The study of internal structure, structures and composition is widely used for a range of expertise and inspections. Examples include investigating the causes of industrial accidents and explosions, accidents in aviation and automobile transport, investigating the causes of fires, etc. However, similar methods are also used in the analysis of suspected forgeries of art objects (paintings, plaques, sculptures). . One of the options is the use of robotic scanners with various multimodal detectors. The system is currently being developed and integrates the existing X-ray scanner with other analytical modalities (XRD, XRF, multispectral imaging and others). System is based on Radalytica’s multi-robot imaging platform. System measures nearly all conventional 2D and 3D trajectories of X-ray imaging with precisely calibrated and repeatable geometrical accuracy leading to a spatial resolution of up to 50 µm. Robotic scanners system opens the door to explore new approaches to both 2D and 3D X-ray imaging, especially in combination with photon-counting detectors. Platform allows combining several imaging modalities with any required number of robots. Such modalities range from visible light imaging, UV, IR, to 3D surface profiling, air-coupled ultrasound to 2D X-ray imaging, and CT. The key parts of the scanner are two robotic stations. One robot carries an X-ray tube whose emission spot size range is 8 – 40 µm, and the operating voltage range is 10 – 130 kVp, and the other one holds a photon-counting imaging detector of the Widepix MPX3 family. Robots can move and rotate freely about the sample in a precisely synchronized movement. It provides almost absolute flexibility of viewing angles. The very high sensitivity, spatial resolution, and dynamic range of the used detectors enable us to push the X-ray image quality to its physical limits. System is equipped with accurate geometrical calibrations that allow positioning both robots precisely yet arbitrarily. Therefore, the robots can be moved to different locations during on-site inspections. The system currently allows a number of default modes: 2D scans (classic non-destructive testing tool), extended Field of View Scan (measuring X-ray images of large, thick parts), Parallel-Beam Scan (overlapping internal structures and varying magnification reduce the readability of X-ray images), Parallel-Extended Scan (parts with a high aspect ratio suffer from parallax artifacts more on the longer dimension), 2.5D Curved Scan (applies to flat parts where the virtual parallel-beam crosses the part perpendicularly). Other new modes are applied: Arbitrary-Path CT Scans (flexibility of positioning enables new types of scanning trajectories, or even a combination of 2D scan strategies at multiple angles and positions to form optimal CT projections given the part accessibility and inner structure), Cone-Beam CT (the CT scans with RadalyX are possible around nearly any arbitrary axis in 3D), Parallel / Helical CT (the tube and detector always move together maintaining their mutual position and taking projections or “views”, the individual “views” are translated and rotated around the object), Multi-Axes CT (multi-axes CT can run selectively along one axis or combinatorial of projections around multiple axes in one scan). Overlapping internal structures and varying magnification reduce the readability of X-ray images. Parallax distortion, resulting from viewing under the diverging angle of cone-beam X-rays, is quite pronounced in parts with dominating orientation of internal structures. Different tomosynthesis scan trajectories was introduced to resolve depth information when the accessibility is limited. The resulting images have correct absolute dimensions at all object depth slices. The method is described as a way to ‘focus the X-ray image to a selected depth’. The full depth data is measured in one scan, and the focused depth is selected easily in the visualization. The projection angles are achieved by either rotating the X-ray tube and the detector or only by the cone-beam angle itself without rotation. The development of the system will focus in the next stages on several areas. The first one is improving the system parameters such as spatial resolution and scanning speed. Another very attractive direction of development is adaptive imaging, i.e. scanning strategies where the measurement path and speed are driven by feedback from measured images. With X-ray imaging alone, it is not possible to obtain all the necessary information about the object under investigation. A typical example is kissing bonds and delamination in composite materials. They are at least extremely difficult to detect with X-rays. On the other hand, ultra-sound testing (UT) based techniques detect these flaws easily. The combination of X-rays with UT is of high interest to the aerospace and other areas of industry. Other modalities to be included are multispectral imaging (macro imaging from UV to SWIR, and VNIR) and XRF chemical analysis and mapping. Another of the tested modalities is energy dispersive X-ray diffraction (EDXRD). The spectral sensitivity of every pixel in AdvaPIX TPX3 camera with high resolution Timepix3 chip enables polychromatic X-ray beam to be used for EDXRD resulting in fast and compact system. A polychromatic X-ray beam generated by a standard X-ray tube with simple (dual stage collimator) without need of monochromator yields high intensity enabling faster and smaller system, much less complex. The high resolution detector placed close to the sample covering a large solid angle => mechanical angular scanning is not needed => fast data accumulation. Broad energy range (3 - 150keV) allows that even very absorbing samples can be analyzed (stainless steel, heavy metals and minerals). The result will be a versatile multimodal system that will enable non-destructive analysis of a wide range of objects. The dual robot, or more general multi-robot, based on RadalyX imaging platform is proving itself not only as a highly flexible non-destructive testing tool but also as versatile research equipment. The flexibility of robots allows applying the system in a wide range of common tasks. It also opens new possibilities and scan approaches impossible otherwise. New possibilities are brought by the tested significant extension of analytical modalities, in particular XRF, XRD, multispectral imaging and others. All measurements are made in a uniform reference system so that the results can be combined, displayed and analysed. The system brings completely new possibilities for forensic analysis, material analysis, art research and industrial inspection [5].

Volume: 30
DOI: https://doi.org/10.1093/mam/ozae044.1094

The Timepix3 readout ASIC chip is a hybrid pixelated radiation detector, designed at CERN, which contains a 256 px × 256 px matrix. Each of the 65,536 radiation-sensitive pixels can record an incoming particle, its energy deposition or time of arrival and measure them simultaneously. Since the detector is suitable for a wide range of applications from particle physics, national security and medicine to space science, it can be used in a wide range of temperatures. Until now, it has to be calibrated every time to the operating point of the application. This paper studies the possibility of energy measurement with Timepix3 equipped with a 500 m thick silicon sensor and MiniPIX readout interface in the temperatures between 10 ∘C and 70 ∘C with only one calibration. The detector has been irradiated by X-ray fluorescence photons in the energy range from 8 keV to 57 keV, and 31 keV to 81 keV photons from the 133Ba radioactive source. A deviation of 5% in apparent energy value may occur for a 10 ∘C change in temperature from the reference point, but, with the next temperature change, it can reach up to −30%. Moreover, Barium photons with an energy of 81 keV appear as deposited energy of only 55 keV at a detector temperature of 70 ∘C . An original compensation method that reduces the relative measurement error from −30% to less than 1% is presented in this paper.

Volume: 23
Issue: 4
Pages: 2201
DOI: https://doi.org/10.3390/s23042201

The hybrid architecture of the Timepix (TPX) family of detectors enables the use of different semiconductor sensors, most commonly silicon (Si), as well as high-density materials such as Cadmium Telluride (CdTe) or Gallium Arsenide (GaAs). For this purpose, we explore the potential of a silicon carbide (SiC) sensor bump-bonded on a Timepix3 detector as a radiation imaging and particle tracking detector. SiC stands as a radiation-hard material also with the ability to operate at elevated temperatures up to several hundreds of degrees Celsius. As a result, this sensor material is more suitable for radiation harsh environments compared to conventional e.g., Si sensors. In this work, we evaluate the response for precise radiation spectrometry and high-resolution particle tracking of newly developed SiC Timepix3 detector which is built and operated as a compact radiation camera MiniPIX-Timepix3 with integrated readout electronics. Calibration measurements were conducted with mono-energetic proton beams with energies of 13, 22, and 31 MeV at the U-120M cyclotron at the Nuclear Physics Institute Czech Academy of Science (NPI CAS), Prague, as well as 100 and 226 MeV at the Proton Therapy Center Czech (PTC) in Prague. High-resolution pattern recognition analysis and single-particle spectral tracking are used for detailed inspection and understanding of the sensor response. Results include distributions of deposited energy and linear energy transfer (LET) spectra. The spatial uniformity of the pixelated detector response is examined in terms of homogeneously distributed deposited energy.

Volume: 18
Article Number: C11004
DOI: https://iopscience.iop.org/article/10.1088/1748-0221/18/11/C11004/meta

We examined the response of the pixel detector Timepix3 with silicon sensor to well-defined fast neutron fields. Part of the pixel detector silicon sensor was additionally equipped with a neutron mask of distinct converter regions. The mask consists of separate thermal and fast neutron regions using 6LiF and hydrogen (plastic) converters, respectively. Measurements were performed with mono-energetic fast neutrons produced at D-D and D-T sources from a Van de Graaff accelerator and a neutron generator, respectively. Data were collected with low background including measurements with moderator material to provide a thermalized neutron component. All the signals produced in the detector were analyzed and decomposed in terms of the spectral-tracking response of the pixel detector. The effect of the fast and thermal components of the neutron converter were determined and compared with direct interactions in the silicon sensor which are significant and can be dominant for fast neutrons. We identify and classify the neutron-induced tracks in terms of the broad-type particle-event track classes. A partial overlap is unavoidable with tracks from direct detection of other radiations in particular protons and low-energy light ions as well as X rays. This will limit the neutron-event discrimination in mixed-radiation fields. The detection response according sensor-mask region was examined and calibrated for the investigated neutron fields. The neutron detection efficiency is selectively derived for the detector particle-event classes. This approach enables to enhance the neutron-discrimination and suppress background and unwanted events. This work enables to extend the response matrix of the detector for broad-type radiations to include neutrons both fast and thermal. The results serve to enhance the sensitivity and determine the neutron component in unknown and mixed-radiation fields such as outer space and particle radiotherapy environments.

Volume: 18
Article Number: P01003
DOI: https://doi.org/10.1088/1748-0221/18/01/P01003

The semiconductor pixel detector Timepix2 is operated with highly integrated readout electronics as a miniaturized and portable MiniPIX TPX2 radiation camera for radiation imaging and spectral-sensitive particle tracking in wide field-of-view. The device provides room-temperature operation, ease of use (single USB 2.0 port), online response with single track visualization, fast frame readout (up to 60 fps) and double per-pixel response for detailed measurements with per-pixel energy and counting or energy and timing sensitivity. We evaluate the response and applicability of a MiniPIX TPX2 camera with the Timepix2 ASIC chip equipped with a 300 µm thick silicon sensor for wide-range composition and spectral characterization of mixed-radiation fields. Measurements were performed in high-energy proton radiotherapy environments with protons of selected energies in the range 225–70 MeV and water-equivalent targets of varying configuration (size, dimension, geometry). High-resolution pattern recognition and spectral-tracking analysis of the single particle tracks in the pixelated detector enable to resolve and classify all detected signals according particle species, direction and energy loss. Based on the experimental calibrations performed with well-defined radiation fields together with quantum imaging visualization of single particle tracks, ten broad-range particle-event classes are resolved. Mixed-radiation fields are thus analyzed according particle-event types in wide range of deposited energy, linear-energy-transfer LET, particle fluxes and dose rates. The spatial distribution over the detector sensor matrix of the distinguished groups can be visualized as well as the directional mapping of energetic charged particles.

Volume: 17
Article Number: C11014
DOI: https://doi.org/10.1088/1748-0221/17/11/C11014

A highly integrated particle telescope is assembled from two MiniPIX Timepix3 detectors in stack configuration to provide time- and spectral-sensitive tracking of energetic charged particles. The telescope architecture, high granularity and per-pixel spectral response of the imaging detectors enable directional mapping of energetic charged particles in wide field-of-view (FoV) with high angular resolution (sub degree) without the need for collimators. The pixel detectors are operated in sync and readout each with separate USB 2.0 cable for integrated control and power supply. Timepix3 two per-pixel signal channels are operated in energy and time mode for detailed spectral- and time-registration of single events in each detector. Events are registered with time stamp resolution at tens of ns level between both detectors. Correlated events between both detector layers are resolved by correlated time stamp with a coincident time window <100 ns. The stack sync configuration allows to perform precise spectrometry (energy loss) and high-resolution tracking over the entire FoV. Particle-event classification is enhanced by spectral and tracking analysis of correlated events in both detectors. The sensors of the detectors can be of different semiconductor material or thickness for selective multiple energy loss ΔE1 + ΔE2 technique. Data products include detailed angular distributions of energetic charged particles with high angular resolution, time stamp, spectral response (energy loss, LET value) and enhanced particle-type resolving power of over 8 event classes. The directional response and angular resolution depend on the spacing gap between the tracker detectors. The resulting field-of-view, geometric factor and angular resolution are evaluated. Results are presented with proof-of-principle of the technique and evaluation of synchronized operation with 31 MeV protons.

Volume: 17
Article Number: C03028
DOI: https://doi.org/10.1088/1748-0221/17/03/C03028

The miniaturized radiation camera MiniPIX TPX3 is designed for detailed and wide-range measurements of mixed-radiation fields present in many applications such as radiotherapy and space radiation in outer orbit. The highly integrated instrumentation utilizes a single connector for control and readout for flexible measurements and quick deployment. The device features an option to process the registered data on the same device with limited resolution and basic particle-type resolving power. A novel readout and data processing technique exploits the detector high granularity and double per-pixel signal electronics to measure and characterize radiation fields of high intensity over a wide range with basic particle-type discrimination.

Volume: 17
Article Number: C03019
DOI: https://doi.org/10.1088/1748-0221/17/03/C03019

The spectral response of the pixel detector Timepix at the high per-pixel proportional range is examined and calibrated using a simple technique and alpha particles from a standard laboratory source in air. For the detector used, a Timepix ASIC chip equipped with a 300 m thick silicon sensor, the spectral range is newly extended up to about 1750 keV per-pixel. This expands and covers the region above 850 keV per pixel which is described and covered by the existing low-energy calibration. The low-energy calibration uses discrete low-energy gamma rays in the range 5–60 keV and is extrapolated over the linear range up to 850 keV/px. Above this level, the per-pixel spectral response changes. At higher energies it undergoes distortion and saturation. The proportional and monotonic response is observed with regions of varying dependence up to nearly 2 MeV. This high-energy region is covered and described by the newly developed calibration method which Uses an alpha source of common low activity (kBq level). Data are collected within one day of total measuring time. Measurements are performed in air at various source-to-distance positions and several sensor bias settings. The developed method together with suitable setting of the sensor bias, which determines the extent of charge sharing, expands the spectral response of Timepix to high energy-loss particles such as alpha particles and light ions in wide energy range. Results are demonstrated on alpha particles, protons and 12C ions. Resulting spectra of deposited energy and cluster pixel height are correctly calibrated and they reproduce expected values.

Volume: 1022
Article Number: 165957
DOI: https://doi.org/10.1016/j.nima.2021.165957

Purpose/Objective(s) We investigated the scattered radiation produced by a collimated proton beam in the case of head and neck cancer using an anthropomorphic head phantom with human-like anatomy, with two dental implants inserted. Using high-resolution semiconductor pixel detectors, we measured and analyzed the backscatter radiation with particle identification resolving power. This research is focused on giving quantitative information about the radiation field components. Materials/Methods A treatment plan was designed on a standard X-ray CT which contained the implants at the center of the tumor. Two irradiations of an anthropomorphic head phantom were performed with clinical proton beams: one without metallic implants (plastic inserts) and one with dental implants. Two titanium cylindrical inserts of 1 cm length and 0.33 cm diameter were placed in the phantom's upper jaw like the molar's replacements. The planning target volume (PTV) is shaped so that the dental inserts are centered in the target volume. A scattered fixed proton beam with a nominal energy of 170 MeV was delivered to the phantom using collimators and boluses designed to shape and stop the beam according to the treatment plan. Scattered primary and secondary radiation was detected with hybrid semiconductor pixel detectors, placed at 4 cm behind the PTV. Detailed description of the mixed-radiation field was performed with spectral (energy loss) and tracking (direction) sensitivity. Results Measurements included a low intensity proton beam to assess the particle tracking response and identification resolving power in both situations (with and without implants). In this manner, the components of the radiation field were observed and analyzed. Based on their characteristic directional-sensitive spectral-track signal in the detector, both primary and secondary protons can be distinguished from light charged particles. This was done by analyzing single particle pixelated clusters morphology, spectral and directional sensitive parameters. Directional fluxes and linear energy transfer (LET) spectra of charged particle groups provide information about the scattered radiation field. Conclusion We present novel information about dental metallic implants' influences in a proton-based treatment. Preliminary results show differences in the LET distributions of the scattered radiation when the implants are in place, respectively, when they are missing. Further analyses will be done to provide a detailed dissemination of contribution for every type of particle. Author Disclosure: C. Balan: None. C. Granja: None. C. Oancea: None. G. Mytsin: None. S. Shvidky: None. A. Molokanov: None. V. Chis: None.

Volume: 114
Article Number: e542
DOI: https://doi.org/10.1016/j.ijrobp.2022.07.2158

The track structure of the signal measured by the semiconductor pixel detector Timepix3 was modelled in the Monte Carlo MCNP® code. A detailed model at the pixel-level (256 × 256 pixels, 55 × 55 µm2 pixel size) was developed and used to generate and store clusters of adjacent hit pixels observed in the measured data because of particle energy deposition path, charge sharing, and drift processes. An analytical model of charge sharing effect and the detector energy resolution was applied to the simulated data. The method will help the user sort the measured clusters and distinguish radiation components of mixed fields by determining the response of Timepix3 detector to particular particle types, energies, and incidence angles that cannot be measured separately.

Volume: 101
DOI: https://doi.org/10.1016/j.ejmp.2022.08.002

The Compton camera concept is based on the reconstruction of recorded Compton scattering events of incoming gamma rays. The scattering of primary gamma ray occurs in the first detector (called scattering detector—usually thin) recording the position and energy of the recoiled electron. The scattered gamma quantum continues towards the second detector (called absorption detector - usually thick) where it is absorbed. The second detector records the energy and the position of this scattered gamma. Using the Compton scattering equation it is possible to determine the scattering angle, and estimate possible directions of the original gamma ray as a surface of a cone. When the Compton camera records the number of such events, the location and the shape of the gamma source can be reconstructed. Timepix3, a hybrid single photon counting imaging pixel detector, is a perfect device for creation of a compact Compton camera. Timepix3 is an event based readout chip (every hit pixel is immediately sent to a readout) and can record the time-of-arrival (ToA) and energy of an incident gamma simultaneously in each pixel. The chip offers high energy resolution (1 keV at 60 keV, 7 keV at 356 keV), as well as time resolution (1.6 ns). The Timepix3 readout chip can be combined with different sensor materials (Si, CdTe, CZT). In this contribution, we present a very compact detector system for imaging with gamma-rays using the Compton camera principle. The system consists of at least two layers of hybrid pixel detectors Timepix3 with the sensors being optimized for gamma-ray tracking. The front detector layer (scattering) is made of silicon of 1 mm thickness, while the last layer (absorbing) is equipped with thick CdTe or CZT sensors up to 2 mm in thickness. The total absorption of the whole detector can be very high if several CdTe or CZT layers are used. The maximal number of layers is not limited, but the practical evaluation was performed with 2 layers. Thanks to Timepix3 simultaneous measurement of ToA and energy, it is possible to precisely detect coincidence events in the detector layers. Based on the energy and position of these events, it is possible to estimate the possible direction of the original gamma. The angular resolution of the presented Compton camera depends on the detected energy, and it is in the order of 1 degree.

DOI: https://doi.org/10.1088/1748-0221/13/11/C11022

The Compton camera concept is based on reconstruction of recorded Compton scattering events for incoming gamma rays. The camera usually consist of two or more position (2D) and energy sensitive detectors. The Compton scattering of the incoming gamma ray recoiling an electron occurs in the first detector. The position and energy of recoiled electron is recorded. The scattered gamma ray continues to the next detector where it is absorbed and its energy and position is recorded too. Knowing both positions and energies the scattering angle can be calculated using the Compton equation. By detecting multiple events the position and image of the gamma source can be reconstructed. The Compton scattering and absorption of the scattered gamma can occur within a single detector too. Such events can be used for reconstruction only if the detector provides information on 3D positions of both events along with their energies. The Timepix3, a hybrid single photon counting pixel detector, is perfect device for such measurements. It can record time-of-arrival (ToA) and energy of incident gamma rays simultaneously in each pixel. In this article we present a concept of miniaturized single layer Compton camera consisting of a single Timepix3 detector with a thick 2 mm CdTe sensor. Thanks to Timepix3 high resolution ToA measurement (1.6 ns), it is possible to measure the drift time of charge transport within the sensor and thus determine the vertical position (depth) of both interactions. By knowing both energy and position of the events in the sensor, we can reconstruct the image of the gamma source. The angular resolution of the presented Compton camera depends on the detected energy and reaches the order of a few degrees.

DOI: https://doi.org/10.1088/1748-0221/15/01/C01014

We evaluate a high-resolution contrast-enhanced method for energy-sensitive radiography of thin samples with low-energy protons at the light-ion Tandetron accelerator of the NPI-CAS in Rez near Prague. We make use of the high-sensitivity of the hybrid semiconductor pixel detectors Timepix enabled by integrated per-pixel signal processing electronics. For this work we use the Timepix3 ASIC chip equipped with a 500 µm Si sensor operated with the fast data rate AdvaPix readout electronics interface. Measurements are performed in air with a 2.9 MeV proton microbeam on thin samples (<100 µm thick). As referential and testing sample we use a set of aluminum foils stacked into a closely packed assembly of varying layers of well-defined thickness. This and other samples were imaged and placed in front of the detector in transmission geometry. Radiographies were collected with focused beam (few mm size) and a microbeam (few µm size). The imaging principle is based on high-resolution spectrometry of single transmitted particles. Contrast is obtained by registration of small differences in the deposited energy of the proton after passing through the sample. This can be measured in wide-range by detailed spectral-tracking analysis of the pixelated clusters in the pixel detector. We examine and evaluate various cluster-track parameters sensitive for imaging contrast such as deposited energy, cluster area (number of pixels) and cluster height (maximum energy value of the pixels in the cluster). The position of interaction in the detector is registered in sub-pixel resolution down to few µm scale for the particles and geometry used. Radiographies are reconstructed based on these individual parameters imaged in image bins of adjustable size (few µm up to few tens of µm). The technique developed with different cluster parameters is presented together with evaluation of image contrast sensitivity on various types of samples and beam energies.

Volume: 17(04)
Article Number: C04016
DOI: https://doi.org/10.1088/1748-0221/17/04/C04016

Volume: 261
Article Number: 01005
DOI: Not available

In this work, Schottky detectors based on a high-quality 4H-SiC epitaxial layer with a thickness of 50 µm were prepared. The Schottky contact of Ni/Au metallization with a 3 mm diameter was made. Reverse current-voltage characteristics were measured up to a voltage of 300 V with a leakage current of 40 pA at room temperature. Using an α-particle radiation source, the spectrometric characteristics of the 4H-SiC detector were tested. The best energy resolution in the FWHM (Full Width and Half Maximum) about 15 keV for 5.5 MeV α-particles was observed. Furthermore, a 4H-SiC pixel sensor (256 × 256) for the Timepix3 reading chip was prepared. The spectrometric and imaging properties of the new Timepix3 detector based on the 4H-SiC sensor were tested. The results showed high energy resolution and also high-quality X-ray imaging of the biological object.

Volume: 17
Article Number: C12005
DOI: https://doi.org/10.1088/1748-0221/17/12/C12005

Small animal SPECT imaging represents a fast-evolving method for a noninvasive molecular imaging of metabolism, diseases, or malfunctions in live animal models. Preclinical imaging is important for translational research related to development and testing of new tracers, diagnostic and therapeutic methods for clinical application, and helps also in basic biological research. The small animal imaging requires better spatial resolution compared to human imaging. The improvement on the detector side should be implemented because the currently used scintillation gamma cameras are now touching their limits. The main goal of this work aims on introduction of a new concept of our prototype system (FullSPECT 3D) and comparison of the performance of its hybrid semiconductor Timepix3 based detector, and standard scintillation gamma camera in a commercially available device (Albira Preclinical Imaging System) for SPECT imaging on phantom and animal model. We compared both detector types on widely used Tc-HDP (for bone scan), and 125I labeled antibody biodistribution assays. The images taken with a single Timepix3 based detector were comparable and in some parameters exceeded standard detectors under similar geometry in 2D projections. The differences in 3D reconstructed images were not calculated because of the huge difference in the reconstruction algorithms, nevertheless the 3D images are shown as well. The future SPECT systems could benefit from the speed, energy resolution and size of Timepix3 based detectors and open the way to construction of very fast multimodal imagers requiring less ionizing radiation delivered to the patient.

Volume: 1032
DOI: https://doi.org/10.1016/j.nima.2022.166531

Pre-treatment proton radiography and computed tomography can improve precision of proton therapy. A compact imaging setup for small-animal proton radiography, based on a miniaturized Timepix detector is presented along with results from proof-of-concept experiments. The MiniPIX detector was placed behind a μ-CT calibration phantom with 10 different tissue-equivalent inserts. The intensity of the 70MeV proton beam was adjusted such that pixel signal clusters from individual protons on the detector could be resolved. Analysis and event filtering on various cluster properties were used to suppress unwanted events. The energy deposition of the selected clusters was converted to water-equivalent thickness (WET) of the traversed material using a conversion curve based on Monte Carlo simulations and measured clusters of protons after traversing PMMA slabs of known thickness. Despite a systematic underestimation of up to 3%, retrieved WET values are in good agreement with ground truth values from literature. The achieved spatial resolution ranges from 0.3 to 0.7 mm for phantom-detector-distances of 1 to 5 cm. Applicability to living animals is currently limited by the relatively long acquisition time of up to 20 minutes per radiography. This obstacle can however be overcome with the latest detector generation Timepix3, allowing to handle higher particle rates and thus requiring shorter irradiation times.

Article Number: 21077049
DOI: 10.1109/NSS/MIC42677.2020.9508073, https://www.researchgate.net/publication/353859285_Proton_Radiography_for_a_Small-Animal_Irradiation_Platform_Based_on_a_Miniaturized_Timepix_Detector

This contribution presents the recent research developments within the Cosmic Ray Extremely Distributed Observatory in the search for resolution of various scientific puzzles, ranging from fundamental physical questions to applications like the determination of earthquake precursors. The state-of-the art theoretical, numerical and computational aspects of these phenomena are addressed, as well as recent experimental developments for detection.

Volume:
Article Number:
DOI: https://rmf.smf.mx/ojs/index.php/rmf-s/article/view/7160

The miniaturized radiation camera MiniPIX TPX3 is designed for detailed and wide-range measurements of mixed-radiation fields present in many applications such as radiotherapy and space radiation in outer orbit. The highly integrated instrumentation utilizes a single connector for control and readout for flexible measurements and quick deployment. The device features an option to process the registered data on the same device with limited resolution and basic particle-type resolving power. A novel readout and data processing technique exploits the detector high granularity and double per-pixel signal electronics to measure and characterize radiation fields of high intensity over a wide range with basic particle-type discrimination.

Volume: 17
Article Number: C03019
DOI: https://doi.org/10.1088/1748-0221/17/03/C03019

We present a miniaturized and wide field-of-view X-ray and Gamma-ray imager consisting of a segmented 2D optics-collimator coupled to the high-sensitivity semiconductor pixel detector Timepix equipped with a high-Z sensor (CdTe 2000 μ m thick). The compact payload has been deployed in low-Earth orbit (LEO) onboard the 3U Cubesat VZLUSAT-2 which was launched on 13 January 2022. The instrument is designed to verify small spacecraft borne observation in open space of hard X-ray and Gamma-ray sources both of celestial and atmospheric origin. High-resolution spectral-sensitive X-ray and Gamma-ray images are provided with enhanced event discrimination and wide field-of-view up to 60°. Description of the instrument together with response evaluation and tests in ground with well-defined sources are presented. The intended observational plan for in-orbit measurements is outlined along with astrophysical goals and issues.

Volume: 8
Article Number: 241
DOI: https://doi.org/10.3390/universe8040241

A Miniaturized Radiation Monitor (MIRAM) has been developed for the continuous measurement of the radiation field composition and ionizing dose rates in near earth orbits. Compared to currently used radiation monitors, the presented device has an order of magnitude lower weight while being comparable in power consumption and functionality. MIRAM is capable of on-board real-time self-diagnostic. Furthermore, it supports on-board analysis of the measured data to be able to work autonomously. The dose rate is calculated continuously based on the energy deposition in the Timepix3 detector. For the estimation of the particle species composition of the radiation environment, two methods are applied depending on the current flux. At lower fluxes (<10 4 particles per cm2 per s), a track-by-track analysis based on temporal coincidence is applied. At higher fluxes, a less power and memory consuming method is utilized. This method is using the averaged deposited energy per pixel to estimate the electron and proton content of the radiation field.

Volume: 17
Article Number: C01066
DOI: 10.1088/1748-0221/17/01/C01066, https://cds.cern.ch/record/2800454

Volume: 12
Issue: 11
Pages: 1835
DOI: Not available

FLASH radiotherapy necessitates the development of advanced Quality Assurance methods and detectors for accurate and online monitoring of the radiation field. This study introduces enhanced time-resolution detection systems and methods tailored for single-pulse detection. The goal of this work was to measure the delivered number of pulses, investigate temporal structure of individual pulses, and to develop a method for dose-per-pulse (DPP) monitoring based on secondary radiation particles produced in the experimental room. A 20 MeV electron beam generated from a linear accelerator (LINAC) was delivered to a water phantom. Ultra-high dose-per-pulse (UHDPP) electron beams were used with a dose per pulse ranging from 1 Gy to over 7 Gy. The pulse lengths ranged from 1.18 us to 2.88 us at a pulse rate frequency of 5 Hz. A semiconductor pixel detector Timepix3 (TPX3) was used to track direct interactions in the Silicon sensor created by single secondary particles. Measurements were performed in the air, while the detector was positioned out-of-field at a lateral distance of 200 cm parallel with the LINAC exit window. The dose deposited in the silicon was measured along with the pulse length and the nanostructure of the pulse. Simultaneously deposited energy and time of arrival of single particles were measured with a precision of 1.56 ns. The measured pulse count agreed with the delivered values. A linear response (R^2 = 0.999) was established between the delivered beam current and the measured dose at the detector position (orders of nGy). The difference between the average measured and average delivered pulse length was 0.003(30) us. This simple non-invasive method, exhibits no limitations on the delivered DPP within the range used during this investigation. It enhances the precision and real-time monitoring of FLASH treatment plans with nanosecond precision.

DOI: https://doi.org/10.48550/arXiv.2404.13732

This work investigates the operational acquisition time limits of Timepix3 and Timepix2 detectors operated in frame mode for high-count rate of high deposited energy transfer particles. Measurements were performed using alpha particles from a 241Am laboratory source and proton and carbon ion beams from a synchrotron accelerator. The particle count rate upper limit is determined by overlapping per-pixel particle signals, identifiable by the hits per pixel counter > 2, indicating the need to decrease acquisition time. On the other hand, the lower limit is the time required to collect the particle deposited charge while maintaining spectral properties. Different acquisition times were evaluated for an AdvaPIX Timepix3 detector (500 μm Silicon sensor) with standard per-pixel Digital to Analog Converter (DAC) settings and a Minipix Timepix2 detector (300 μm Silicon sensor) with standard and customized settings the pulse shaping parameter and threshold. For AdvaPIX Timepix3, spectra remained accurate down to 100 μs frame acquisition time; at 10 μs, loss of collected charge occurred, suggesting either avoiding this acquisition time or applying a correction. Timepix2 allowed acquisition times down to 100 ns for single particle track measurements even for high energy loss, enabled by a new Timepix2 feature delaying shutter closure until full particle charge collection. This work represents the first measurement utilizing Timepix-chips pixel detectors in an accelerator beam of clinical energy and intensity without the need to decrease the beam current. This is made possible by exploiting the short shutter feature in Timepix2 and a customized per-pixel energy calibration of the Timepix2 detector with a larger discharging signal value which allowed for shorter Time-over-Threshold (ToT) signal. These customized settings extend the operation of the pixel detectors to higher event rates up to 10 9 particles/cm2/s.

Volume: 19 (11)
Article Number: C11002
DOI: https://iopscience.iop.org/article/10.1088/1748-0221/19/11/C11002

This study investigates the response of Timepix3 semiconductor pixel detectors in proton beams of varying intensities, with a focus on FLASH proton therapy. Using the Timepix3 ASIC chip, we measured the spatial and spectral characteristics of 220 MeV proton beams delivered in short pulses. The experimental setup involved Minipix readout electronics integrated with a Timepix3 chipboard in a flexible architecture, and an Advapix Timepix3 with a silicon sensor. Measurements were carried out with Timepix3 detectors equipped with GaAs and silicon Si sensors. We also investigated the response of a bare Timepix3 ASIC chip (without a sensor). The detectors were placed within a waterproof holder attached to the IBA Blue water phantom, with additional measurements performed in air behind a 2 cm-thick solid phantom. The results demonstrated the capability of the Timepix3 detectors to measure time-over-threshold (ToT) and count rate (number of events) in both conventional and ultra-high-dose-rates proton beams. The bare ASIC chip configuration sustained up to a dose rate (DR) of 270 Gy/s, although it exhibited limited spatial resolution due to low detection efficiency. In contrast, Minipix Timepix3 with experimental GaAs sensors showed saturation at low DR=5 Gy/s. Furthermore, the Advapix Timepix3 detector was used in standard and customized configurations. In the standard configuration (Ikrum =5), the detector showed saturation at DR=5 Gy/s. But, in the customized configuration when the per-pixel discharging signal (Ikrum) was increased to 80, the detector demonstrated enhanced performance by reducing the duration of the ToT signal, allowing beam spot imaging up to DR=28 Gy/s in the plateau region of the Bragg curve. For such DR, the frame acquisition time was reduced to the order of microseconds, meaning only a fraction of the pulse (with pulse lengths on the order of milliseconds) was captured.

DOI: https://doi.org/10.48550/arXiv.2410.00549

This study experimentally examines the effect and changes in the delivered fields, using water-equivalent phantoms with and without titanium (Ti) dental implants positioned along the primary beam path. We measure in detail the composition and spectral-tracking characterization of particles generated in the entrance region of the Bragg curve using high-spatial resolution, spectral and time-sensitive imaging detectors with a pixelated array provided by the ASIC chip Timepix3. A 170 MeV proton beam was collimated and modulated in a polymethyl methacrylate (PMMA). Placing two dental implants at the end of the protons range in the phantom, the radiation was measured using two pixeled detectors with Si sensors. The Timepix3 (TPX3) detectors equipped with silicon sensors measure in detail particle fluxes, dose rates (DR) and linear energy transfer (LET) spectra for resolved particle types. Artificial intelligence (AI) based-trained neural networks (NN) calibrated in well-defined radiation fields were used to analyze and identify particles based on morphology and characteristic spectral-tracking response. The beam was characterized and single-particle tracks were registered and decomposed into particle-type groups. The resulting particle fluxes in both setups are resolved into three main classes of particles: i) protons, ii) electrons and photons iii) ions. Protons are the main particle component responsible for dose deposition. High-energy transfer particles (HETP), namely ions exhibited differences in both dosimetric aspects that were investigated: DR and particle fluxes, when the Ti implants were placed in the setup. The detailed multi-parametric information of the secondary radiation field provides a comprehensive understanding of the impact of Ti materials in proton therapy.

DOI: https://doi.org/10.48550/arXiv.2409.18521

Purpose 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. Methods A pixelated semiconductor detector, AdvaPIX-Timepix3, with a temporal resolution of 1.56 ns, 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. Results 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 7 µs and 1 ms repetition time for the synchrocyclotron accelerator. Conclusion 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.

Volume: 25
Article Number: e14486
DOI: https://doi.org/10.1002/acm2.14486

Background Ultra high dose rate (UHDR) radiotherapy using ridge filter is a new treatment modality known as conformal FLASH that, when optimized for dose, dose rate (DR), and linear energy transfer (LET), has the potential to reduce damage to healthy tissue without sacrificing tumor killing efficacy via the FLASH effect. Purpose Clinical implementation of conformal FLASH proton therapy has been limited by quality assurance (QA) challenges, which include direct measurement of UHDR and LET. Voxel DR distributions and LET spectra at planning target margins are paramount to the DR/LET-related sparing of organs at risk. We hereby present a methodology to achieve experimental validation of these parameters. Methods Dose, DR, and LET were measured for a conformal FLASH treatment plan involving a 250-MeV proton beam and a 3D-printed ridge filter designed to uniformly irradiate a spherical target. We measured dose and DR simultaneously using a 4D multi-layer strip ionization chamber (MLSIC) under UHDR conditions. Additionally, we developed an “under-sample and recover (USRe)” technique for a high-resolution pixelated semiconductor detector, Timepix3, to avoid event pile-up and to correct measured LET at high-proton-flux locations without undesirable beam modifications. Confirmation of these measurements was done using a MatriXX PT detector and by Monte Carlo (MC) simulations. Results MC conformal FLASH computed doses had gamma passing rates of >95% (3 mm/3% criteria) when compared to MatriXX PT and MLSIC data. At the lateral margin, DR showed average agreement values within 0.3% of simulation at 100 Gy/s and fluctuations ∼10% at 15 Gy/s. LET spectra in the proximal, lateral, and distal margins had Bhattacharyya distances of <1.3%. Conclusion Our measurements with the MLSIC and Timepix3 detectors shown that the DR distributions for UHDR scenarios and LET spectra using USRe are in agreement with simulations. These results demonstrate that the methodology presented here can be used effectively for the experimental validation and QA of FLASH treatment plans.

Volume: 51
DOI: https://doi.org/10.1002/mp.17359

Ion-beam radiotherapy is an advanced cancer treatment modality offering steep dose gradients and a high biological effectiveness. These gradients make the therapy vulnerable to patient-setup and anatomical changes between treatment fractions, which may go unnoticed. Charged fragments from nuclear interactions of the ion beam with the patient tissue may carry information about the treatment quality. Currently, the fragments escape the patient undetected. Inter-fractional in-vivo treatment monitoring based on these charged nuclear fragments could make ion-beam therapy safer and more efficient. We developed an ion-beam monitoring system based on 28 hybrid silicon pixel detectors (Timepix3) to measure the distribution of fragment origins in three dimensions. The system design choices as well as the ion-beam monitoring performance measurements are presented in this manuscript. A spatial resolution of along the beam axis was achieved for the measurement of individual fragment origins. Beam-range shifts of were identified in a clinically realistic treatment scenario with an anthropomorphic head phantom. The monitoring system is currently being used in a prospective clinical trial at the Heidelberg Ion Beam Therapy Centre for head-and-neck as well as central nervous system cancer patients.

Volume: 14
Article Number: 15452
DOI: https://doi.org/10.1038/s41598-024-66266-9

Volume: 12
Article Number: 100340

This review explores current experimental methods for determining the radiation quality in ion beams. In this context, radiation quality is commonly evaluated using the averaged linear energy transfer (LET), a metric employed to assess the response of both biological and physical systems. Dose and averaged LET can be experimentally determined with passive detectors through various techniques that have seen recent improvements. Another metric related to the LET is the mean lineal energy, which is measurable using microdosimetric detectors. This review focuses on the available possibilities for evaluating the radiation quality using three microdosimeters (mini-TEPC, Silicon Telescope, and SOI Microplus), three passive luminescence detectors (based on optical, thermo-, and radiophoto-luminescence), three track-based detectors (track-etched detector, Timepix, fluorescent nuclear track detector), and a chemical detector based on alanine. A comparison of detector properties is provided along with an overview of the underlying mechanisms enabling LET assessment or measurements of the mean lineal energy with each detector type. Finally, this review summarizes the current possibilities of LET determination with respect to the needs for quality assurance in particle therapy. Areas for future research and development are suggested.

Volume: 117
Article Number: 107252
DOI: https://doi.org/10.1016/j.radmeas.2024.107252

Objective. This work presents a method for enhanced detection, imaging, and measurement of the thermal neutron flux. Approach. Measurements were performed in a water tank, while the detector is positioned out-of-field of a 20 MeV ultra-high pulse dose rate electron beam. A semiconductor pixel detector Timepix3 with a silicon sensor partially covered by a 6LiF neutron converter was used to measure the flux, spatial, and time characteristics of the neutron field. To provide absolute measurements of thermal neutron flux, the detection efficiency calibration of the detectors was performed in a reference thermal neutron field. Neutron signals are recognized and discriminated against other particles such as gamma rays and x-rays. This is achieved by the resolving power of the pixel detector using machine learning algorithms and high-resolution pattern recognition analysis of the high-energy tracks created by thermal neutron interactions in the converter. Main results. The resulting thermal neutrons equivalent dose was obtained using conversion factor (2.13(10) pSv·cm2) from thermal neutron fluence to thermal neutron equivalent dose obtained by Monte Carlo simulations. The calibrated detectors were used to characterize scattered radiation created by electron beams. The results at 12.0 cm depth in the beam axis inside of the water for a delivered dose per pulse of 1.85 Gy (pulse length of 2.4 μs) at the reference depth, showed a contribution of flux of 4.07(8) × 103 particles·cm−2·s−1 and equivalent dose of 1.73(3) nSv per pulse, which is lower by ∼9 orders of magnitude than the delivered dose. Significance. The presented methodology for in-water measurements and identification of characteristic thermal neutrons tracks serves for the selective quantification of equivalent dose made by thermal neutrons in out-of-field particle therapy.

Date: 14 sept 2023
Volume: 68
Article Number: 185017
DOI: https://doi.org/10.1088/1361-6560/acf2e1

Stray radiation produced by ultra-high dose-rates (UHDR) proton pencil beams is characterized using ASIC-chip semiconductor pixel detectors. A proton pencil beam with an energy of 220 MeV was utilized to deliver dose rates (DR) ranging from conventional radiotherapy DRs up to 270 Gy/s. A MiniPIX Timepix3 detector equipped with a silicon sensor and integrated readout electronics was used. The chip-sensor assembly and chipboard on water-equivalent backing were detached and immersed in the water-phantom. The deposited energy, particle flux, DR, and the linear energy transfer (LET(Si)) spectra were measured in the silicon sensor at different positions both laterally, at different depths, and behind the Bragg peak. At low-intensity beams, the detector is operated in the event-by-event data-driven mode for high-resolution spectral tracking of individual particles. This technique provides precise energy loss response and LET(Si) spectra with radiation field composition resolving power. At higher beam intensities a rescaling of LET(Si) can be performed as the distribution of the LET(Si) spectra exhibits the same characteristics regardless of the delivered DR. The integrated deposited energy and the absorbed dose can be thus measured in a wide range. A linear response of measured absorbed dose was obtained by gradually increasing the delivered DR to reach UHDR beams. Particle tracking of scattered radiation in data-driven mode could be performed at DRs up to 0.27 Gy/s. In integrated mode, the saturation limits were not reached at the measured out-of-field locations up to the delivered DR of over 270 Gy/s. A good agreement was found between measured and simulated absorbed doses.

Volume: 106
Page: 102529
DOI: https://doi.org/10.1016/j.ejmp.2023.102529

Objective. Protons have advantageous dose distributions and are increasingly used in cancer therapy. At the depth of the Bragg peak range, protons produce a mixed radiation field consisting of low- and high-linear energy transfer (LET) components, the latter of which is characterized by an increased ionization density on the microscopic scale associated with increased biological effectiveness. Prediction of the yield and LET of primary and secondary charged particles at a certain depth in the patient is performed by Monte Carlo simulations but is difficult to verify experimentally. Approach. Here, the results of measurements performed with Timepix detector in the mixed radiation field produced by a therapeutic proton beam in water are presented and compared to Monte Carlo simulations. The unique capability of the detector to perform high-resolution single particle tracking and identification enhanced by artificial intelligence allowed to resolve the particle type and measure the deposited energy of each particle comprising the mixed radiation field. Based on the collected data, biologically important physics parameters, the LET of single protons and dose-averaged LET, were computed. Main results. An accuracy over 95% was achieved for proton recognition with a developed neural network model. For recognized protons, the measured LET spectra generally agree with the results of Monte Carlo simulations. The mean difference between dose-averaged LET values obtained from measurements and simulations is 17%. We observed a broad spectrum of LET values ranging from a fraction of keV μm−1 to about 10 keV μm−1 for most of the measurements performed in the mixed radiation fields. Significance. It has been demonstrated that the introduced measurement method provides experimental data for validation of LETD or LET spectra in any treatment planning system. The simplicity and accessibility of the presented methodology make it easy to be translated into a clinical routine in any proton therapy facility.

Volume: 68
Issue: 9
DOI: https://doi.org/10.1088/1361-6560/acc9f8

Position and directional-sensitive spectrometry of energetic charged particles can be performed with high resolution and wide dynamic range (energy, direction) with the hybrid semiconductor pixel detectors Timepix/Timepix3. The choice of semiconductor sensor material, thickness, and properties such as the reverse bias voltage, greatly determine detector sensitivity and resolving power for spectrometry and particle tracking. We investigated and evaluated the spectral tracking resolving power such as deposited energy and linear-energy-transfer (LET) spectra with the Timepix3 detector with different semiconductor sensors, based on GaAs:Cr, CdTe, and Si, using well-defined radiation sources in terms of radiation type (protons), energy, and incident direction to the detector sensor. Measurements of particle incident direction in a wide range were performed with collimated monoenergetic proton beams of various energies in the range 8–31 MeV at the U120-M cyclotron at the NPI CAS Rez near Prague. All detectors were per-pixel calibrated. This work enables to examine and perform a detailed study of charge sharing and charge collection efficiency in semiconductor sensors. The results serve to optimise the detector chip-sensor assembly configuration for measurements especially with high-LET particles in ion radiotherapy and outer space. The work underway includes evaluation of newly refined semi-insulating GaAs sensors and improved radiation hard semiconductor sensors SiC.

Volume: 18
Article Number: C01022
DOI: https://doi.org/10.1088/1748-0221/18/01/C01022

Objective. The lateral dose fall-off in proton pencil beam scanning (PBS) technique remains the preferred choice for sparing adjacent organs at risk as opposed to the distal edge due to the proton range uncertainties and potentially high relative biological effectiveness. However, because of the substantial spot size along with the scattering in the air and in the patient, the lateral penumbra in PBS can be degraded. Combining PBS with an aperture can result in a sharper dose fall-off, particularly for shallow targets. Approach. The aim of this work was to characterize the radiation fields produced by collimated and uncollimated 100 and 140 MeV proton beams, using Monte Carlo simulations and measurements with a MiniPIX-Timepix detector. The dose and the linear energy transfer (LET) were then coupled with published in silico biophysical models to elucidate the potential biological effects of collimated and uncollimated fields. Main results. Combining an aperture with PBS reduced the absorbed dose in the lateral fall-off and out-of-field by 60%. However, the results also showed that the absolute frequency-averaged LET (LETF) values increased by a maximum of 3.5 keV μm−1 in collimated relative to uncollimated fields, while the dose-averaged LET (LETD) increased by a maximum of 7 keV μm−1. Despite the higher LET values produced by collimated fields, the predicted DNA damage yields remained lower, owing to the large dose reduction. Significance. This work demonstrated the dosimetric advantages of combining an aperture with PBS coupled with lower DNA damage induction. A methodology for calculating dose in water derived from measurements with a silicon-based detector was also presented. This work is the first to demonstrate experimentally the increase in LET caused by combining PBS with aperture, and to assess the potential DNA damage which is the initial step in the cascade of events leading to the majority of radiation-induced biological effects.

Volume: 68
Issue: 6
DOI: https://doi.org/10.1088/1361-6560/acbe8d

Objective. The aim of this study was to investigate the feasibility of online monitoring of irradiation time (IRT) and scan time for FLASH proton radiotherapy using a pixelated semiconductor detector. Approach. Measurements of the time structure of FLASH irradiations were performed using fast, pixelated spectral detectors based on the Timepix3 (TPX3) chips with two architectures: AdvaPIX-TPX3 and Minipix-TPX3. The latter has a fraction of its sensor coated with a material to increase sensitivity to neutrons. With little or no dead time and an ability to resolve events that are closely spaced in time (tens of nanoseconds), both detectors can accurately determine IRTs as long as pulse pile-up is avoided. To avoid pulse pile-up, the detectors were placed well beyond the Bragg peak or at a large scattering angle. Prompt gamma rays and secondary neutrons were registered in the detectors' sensors and IRTs were calculated based on timestamps of the first charge carriers (beam-on) and the last charge carriers (beam-off). In addition, scan times in x, y, and diagonal directions were measured. The experiment was carried out for various setups: (i) a single spot, (ii) a small animal field, (iii) a patient field, and (iv) an experiment using an anthropomorphic phantom to demonstrate in vivo online monitoring of IRT. All measurements were compared to vendor log files. Main results. Differences between measurements and log files for a single spot, a small animal field, and a patient field were within 1%, 0.3% and 1%, respectively. In vivo monitoring of IRTs (95–270 ms) was accurate within 0.1% for AdvaPIX-TPX3 and within 6.1% for Minipix-TPX3. The scan times in x, y, and diagonal directions were 4.0, 3.4, and 4.0 ms, respectively. Significance. Overall, the AdvaPIX-TPX3 can measure FLASH IRTs within 1% accuracy, indicating that prompt gamma rays are a good surrogate for primary protons. The Minipix-TPX3 showed a somewhat higher discrepancy, likely due to the late arrival of thermal neutrons to the detector sensor and lower readout speed. The scan times (3.4 ± 0.05 ms) in the 60 mm distance of y-direction were slightly less than (4.0 ± 0.06 ms) in the 24 mm distance of x-direction, confirming the much faster scanning speed of the Y magnets than that of X. Diagonal scan speed was limited by the slower X magnets.

Volume: 68
Article Number: 145018
DOI: https://iopscience.iop.org/article/10.1088/1361-6560/acdc7c/meta

This study aims to assess the composition of scattered particles generated in proton therapy for tumours situated proximal to titanium 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 tumour. A conformal proton beam was used to deliver the treatment plan to an anthropomorphic head phantom with two types of implants (Ti and plastic) inserted in the target volume. The stray radiation resulting 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 convolution neural networks (AI CNN). Spectral sensitive aspects of the scattered radiation were collected using two angular positions of the detector relative to the beam direction: 0 and 60°. Using AI CNN, 3 classes of particles were identified: protons, electrons & photons, ions & fast neutrons. Placing a Ti implant in the beam's path resulted in predominantly electrons and photons, contributing 52.2%, whereas for plastic implants, the contribution was 65.4%. Scattered protons comprised 45.5% and 31.9% with and without Ti inserts, respectively. The LET spectra was derived for each group of particles, with values ranging from 0.01 to 7.5 keV{\mu}m-1 for Ti/plastic implants. The low-LET component was primarily composed of electrons and photons, while the high-LET component corresponded to protons and ions. This method, complemented by directional maps, holds potential for evaluating and validating treatment plans involving stray radiation near organs at risk, offering precise discrimination of the mixt field, enhancing in this way the LET calculation.

DOI: https://doi.org/10.48550/arXiv.2312.14304

Secondary radiation fields encountered in proton radiotherapy environments contain different particle species produced in a broad range of energies and directions. Experimental knowledge of the composition and spectral characteristics of such complex fields is valuable for operation and protection of instruments and personnel, design and optimization of irradiations as well as planning and validation of treatment plans. The neutron component, which are produced with non-negligible yield, is in particular challenging to measure and discriminate from other radiations by conventional detectors. In order to measure in such complex fields the neutron component, both fast and thermal, we make use of the semiconductor pixel detector Timepix3 equipped with a silicon sensor and a neutron converter mask. The detector was before calibrated with well-defined neutron fields. In this work, we characterize the secondary radiation field and examine in particular the neutron component behind a large water-equivalent phantom irradiated by a 190 MeV clinical proton beam. The detected neutrons have a predominant fast neutron component. No thermal neutrons are observed in the measured data. The neutron-induced interactions in the detector are resolved in a high background with enhanced discrimination by quantum-imaging visualization, micrometer scale pattern recognition and high-resolution spectral-sensitive tracking of single particles. Detailed results are provided in wide range in terms of composition of the mixed-radiation field, total and partial fluxes and dose rates as well as particle deposited dose and linear-energy-transfer (LET) spectra.

Volume: 18
Article Number: C11011
DOI: https://doi.org/10.1088/1748-0221/18/11/C11011

Particle therapy can largely benefit from the detailed and wide-range spectrometric and directional characterization of energetic charged particles provided by compact Timepix detectors. Among several physical quantities that can be derived, the assessment of the linear energy transfer (LET) which is based on the deposited energy and particle's track length remains challenging. Due to the detector's pixel pitch, sensor thickness and charge sharing effect, an accurate estimation of the particle's incident angle and hence the track length, has been limited to particles with incident angles greater than 20⁰ with respect to the normal of the sensor layer. This is critical for clinical beams which are highly directional, and measurements with radiation detectors are generally performed with sensitive volumes orthogonally placed with respect to the beam direction. In this work, we present a novel method in which we exploit the morphological cluster parameters to derive the proton's incident angle, thus enabling a precise directional reconstruction over the full field-of-view 2π (solid angle), and within 2° from the reference angles for Timepix detectors with 300 and 500 μm thick Si sensors. As a consequence, the calculation of the track length was also improved, resulting in a more precise LET estimation. The experimental LET spectra and the frequency-averaged LET (LETF) were compared against Monte Carlo simulations using TOPAS for a wide range of proton energies (12 MeV–200 MeV) and incident angles (0–85⁰). An agreement within 12% was found between measured and simulated LETF. A comparison with LET values based on the PSTAR database also showed an agreement within 10%. We demonstrated the feasibility of a precise LET calculation and directional response with an improved angular resolution down to normal incidence using a single-layer Timepix detector, while avoiding the use of a stacked telescope array.

Volume: 199
Article Number: 110349
DOI: https://doi.org/10.1016/j.radphyschem.2022.110349

This work aims to characterize ultra-high dose rate pulses (UHDpulse) electron beams using the hybrid semiconductor pixel detector. The Timepix3 (TPX3) ASIC chip was used to measure the composition, spatial, time, and spectral characteristics of the secondary radiation fields from pulsed 15–23 MeV electron beams. The challenge is to develop a single compact detector that could extract spectrometric and dosimetric information on such high flux short-pulsed fields. For secondary beam measurements, PMMA plates of 1 and 8 cm thickness were placed in front of the electron beam, with a pulse duration of 3.5 µs. Timepix3 detectors with silicon sensors of 100 and 500 µm thickness were placed on a shifting stage allowing for data acquisition at various lateral positions to the beam axis. The use of the detector in FLEXI configuration enables suitable measurements in-situ and minimal self-shielding. Preliminary results highlight both the technique and the detector's ability to measure individual UHDpulses of electron beams delivered in short pulses. In addition, the use of the two signal chains per-pixel enables the estimation of particle flux and the scattered dose rates (DRs) at various distances from the beam core, in mixed radiation fields.

Volume: 17
Article Number: C01003
DOI: 10.1088/1748-0221/17/01/C01003

Volume: 261
Article Number: 01007
DOI: Not available

The track structure of the signal measured by the semiconductor pixel detector Timepix3 was modelled in the Monte Carlo MCNP® code. A detailed model at the pixel-level (256 × 256 pixels, 55 × 55 µm2 pixel size) was developed and used to generate and store clusters of adjacent hit pixels observed in the measured data because of particle energy deposition path, charge sharing, and drift processes. An analytical model of charge sharing effect and the detector energy resolution was applied to the simulated data. The method will help the user sort the measured clusters and distinguish radiation components of mixed fields by determining the response of Timepix3 detector to particular particle types, energies, and incidence angles that cannot be measured separately.

Volume: 101
Pages: 79-86
DOI: 10.1016/j.ejmp.2022.08.002, https://www.sciencedirect.com/science/article/pii/S1120179722020269

Volume: 66
Issue: 4
Pages: 045003
DOI: https://doi.org/10.1088/1361-6560/abdfda

We developed a highly-selective technique to measure the energy loss and linear-energy-transfer (LET) spectra of energetic charged particles in high-resolution and over a large collection of particle-event types. Precise and wide-range spectral and tracking measurements were performed with a single semiconductor pixel detector. The quantum-counting sensitivity, high-granularity and per-pixel spectrometric response of the Timepix ASIC chip enable the detailed spectral-tracking registration of single charged particles across the detector semiconductor sensor. Both the deposited energy along the particle trajectory (energy loss) and the path length of the particle track across the semiconductor sensor are precisely measured for each particle. This allows for the determination of the particle LET in silicon in high accuracy and over a wide-range of energies, particle types and directions. The tracking and energy loss response together with the resolving power at the particle-event level make it possible to selectively provide LET distributions of the light and heavy charged particle components in mixed-radiation and omnidirectional fields. This technique applies to energetic (E 10 MeV/u) charged particles generating tracks greater than the pixel size and incident at non-perpendicular direction ( ) to the sensor plane. The technique applies also to electrons of energy above few MeV as well as highly energetic and minimum-ionizing-particles (MIPs). We make use of existing and in part newly collected data at well-defined radiation fields with proton and light ion beam accelerators. Flexible measurements, ease of deployment and online response are possible by the use of compact readout electronics such as the miniaturized radiation camera MiniPix (size 8 cm, weight 50 g) operable by any PC. Results are given for protons and light ions (He, C) of selected energies above 10 MeV/u and directions (2 FoV). We include also electrons (20 MeV). Selective and detailed LET spectra are produced over a wide range (10−1 to 102 keV/ m) in silicon.

Volume: 988
Article Number: 164901
DOI: 10.1016/j.nima.2020.164901, https://www.sciencedirect.com/science/article/abs/pii/S0168900220312985

Purpose Ion beam radiotherapy offers enhances dose conformity to the tumor volume while better sparing healthy tissue compared to conventional photon radiotherapy. However, the increased dose gradient also makes it more sensitive to uncertainties. While the most important uncertainty source is the patient itself, the beam delivery is also subject to uncertainties. Most of the proton therapy centers used cyclotrons, which deliver typically a stable beam over time, allowing a continuous extraction of the beam. Carbon-ion beam radiotherapy (CIRT) in contrast uses synchrotrons and requires a larger and energy-dependent extrapolation of the nozzle-measured positions to obtain the lateral beam positions in the isocenter, since the nozzle-to-isocenter distance is larger than for cyclotrons. Hence, the control of lateral pencil beam positions at isocenter in CIRT is more sensitive to uncertainties than in proton radiotherapy. Therefore, an independent monitoring of the actual lateral positions close to the isocenter would be very valuable and provide additional information. However, techniques capable to do so are scarce, and they are limited in precision, accuracy and effectivity. Methods The detection of secondary ions (charged nuclear fragments) has previously been exploited for the Bragg peak position of C-ion beams. In our previous work, we investigated for the first time the feasibility of lateral position monitoring of pencil beams in CIRT. However, the reported precision and accuracy were not sufficient for a potential implementation into clinical practice. In this work, it is shown how the performance of the method is improved to the point of clinical relevance. To minimize the observed uncertainties, a mini-tracker based on hybrid silicon pixel detectors was repositioned downstream of an anthropomorphic head phantom. However, the secondary-ion fluence rate in the mini-tracker rises up to 1.5 × 105 ions/s/cm2, causing strong pile-up of secondary-ion signals. To solve this problem, we performed hardware changes, optimized the detector settings, adjusted the setup geometry and developed new algorithms to resolve ambiguities in the track reconstruction. The performance of the method was studied on two treatment plans delivered with a realistic dose of 3 Gy (RBE) and averaged dose rate of 0.27 Gy/s at the Heidelberg Ion-Beam Therapy Center (HIT) in Germany. The measured lateral positions were compared to reference beam positions obtained either from the beam nozzle or from a multi-wire proportional chamber positioned at the room isocenter. Results The presented method is capable to simultaneously monitor both lateral pencil beam coordinates over the entire tumor volume during the treatment delivery, using only a 2-cm2 mini-tracker. The effectivity (defined as the fraction of analyzed pencil beams) was 100%. The reached precision of (0.6 to 1.5) mm and accuracy of (0.5 to 1.2) mm are in line with the clinically accepted uncertainty for QA measurements of the lateral pencil beam positions. Conclusions It was demonstrated that the performance of the method for a non-invasive lateral position monitoring of pencil beams is sufficient for a potential clinical implementation. The next step is to evaluate the method clinically in a group of patients in a future observational clinical study.

Pages: 4411-4424
DOI: 10.1002/mp.15018, https://www.sciencegate.app/document/10.1002/mp.15018

A precise characterization of therapeutic proton pencil beams is essential for the commissioning of any treatment planning system (TPS). The dose profile characterization includes measurement of the beam lateral dose profile in the beam core and far from the beam core, in the so called low-dose envelope, and requires a sophisticated detection system with a few orders of magnitude dynamic range. We propose the use of a single-quantum-sensitive MINIPIX TIMEPIX detector, along with an in-house-designed holder to perform measurements of the pencil beam dose profile in air and in water. We validated the manufacturer calibration of the MINIPIX TIMEPIX detector in proton beams of various energies and compared the deposited energy spectra to Monte Carlo (MC) simulations. The precision of the lateral dose profile measurements has been systematically validated against Krakow proton facility commissioning data and dose profile simulations performed with MC codes Gate/Geant4 and Fred. We obtained an excellent agreement between MINIPIX TIMEPIX measurements and simulations demonstrating the feasibility of the system for a simple characterization and validation of proton pencil beams. The proposed approach can be implemented at any proton therapy facility to acquire experimental data needed to commission and validate analytical and MC-based TPS.

Volume: 0
Article Number: 346
DOI: https://doi.org/10.3389/FPHY.2020.00346

Spectroscopy-based photon-counting detector systems, Medipix, have many applications in medicine. Medipix detectors benefit from providing energy information as well as high spatial resolution. In this article, a review of Medipix detector technology applied to medicine and imaging techniques are presented. The technology has been used to develop quality assurance (QA) measurement devices in radiation-based treatments. A gamma camera system for radiotherapy has been developed to measure dose delivered to prostate treatments in real-time. The advantage of a high-resolution detector has been utilized in proton and heavy ion therapy for dose QA, measuring the charge particle spectra, and beam geometry for mini-beams. Applications in medical imaging using helium ion beams have been investigated to replace CT for ion beam radiotherapy. This technique provides many advantages over conventional CT such as high-resolution imaging and spectroscopy-based information for planning in helium ion treatments. The Medipix technology has shown it can be broadly applied in radiation and particle therapy applications for accurate QA as well as proving high-resolution imaging in medicine.

Volume: 130
Page Range: 106211
DOI: 10.1016/j.radmeas.2019.106211, https://www.sciencedirect.com/science/article/pii/S1350448719304974

For fast neutron sources, such as compact neutron generators, it is desirable to have knowledge and ideally directly measure the energy spectrum of the generated neutrons. For neutrons, the produced radiation field, and the neutron energy spectrum, at a specific location from the source, can be altered by the distance to the source and become even significantly distorted by surrounding material — e.g. walls and the floor of the laboratory. To achieve this goal, we make use of the Time-of-Flight (ToF) technique, which has been implemented on the Timepix3 detector operated in highly integrated readout electronics as a miniaturized radiation camera MiniPIX-Timepix3. Equipped with a silicon sensor, the Timepix3 ASIC chip provides fast timing response of individual pixels at the nanosecond level. In this work, we use two Timepix3 detectors with a silicon ensor of thickness 300 μm and a segmented neutron conversion mask, intended for both thermal and fast neutrons and with a 65 μm thick silicon carbide (SiC) sensor. Demonstration and evaluation of the technique are provided by measurements with a compact neutron D-T pulsed generator at VSB-TU Ostrava laboratory which produces mono-energetic 14MeV neutrons.

Volume: J. of Instrum. JINST 20 (2025)
Article Number: C03045
DOI: https://doi.org/10.1088/1748-0221/20/03/C03045

Silicon Carbide is a suitable semiconductor sensor for radiation measurement and nuclear applications. It has been recently implemented as a position-sensitive and radiation imaging device coupled to the Timepix3 ASIC chip in the form of a miniaturized radiation camera MiniPIX-Timepix3 SiC. In this work we systematically evaluate the detection resolving power to different radiation species: electrons, fast neutrons, ions and protons. Experimental calibrations were made at well-defined reference fields in terms of particle type, energy and direction. The spectral-sensitive tracking response and characteristic morphology of the particle tracks are analyzed by pattern recognition algorithms. The low thickness of the radiation sensitive volume (65 μm) of the SiC sensor limits the directional tracking response and angular resolution. Three broad classes of particle-type events are resolved. The detector together with suitable data processing can be used for radiation dosimetry and particle tracking tasks in space, particle therapy, nuclear physics and nuclear reactors and particle accelerator environments.

Volume: 19
Article Number: C11007
DOI: 10.1088/1748-0221/19/11/C11007

We examined the response of the pixel detector Timepix3 with silicon sensor to well-defined fast neutron fields. Part of the pixel detector silicon sensor was additionally equipped with a neutron mask of distinct converter regions. The mask consists of separate thermal and fast neutron regions using 6LiF and hydrogen (plastic) converters, respectively. Measurements were performed with mono-energetic fast neutrons produced at D-D and D-T sources from a Van de Graaff accelerator and a neutron generator, respectively. Data were collected with low background including measurements with moderator material to provide a thermalized neutron component. All the signals produced in the detector were analyzed and decomposed in terms of the spectral-tracking response of the pixel detector. The effect of the fast and thermal components of the neutron converter were determined and compared with direct interactions in the silicon sensor which are significant and can be dominant for fast neutrons. We identify and classify the neutron-induced tracks in terms of the broad-type particle-event track classes. A partial overlap is unavoidable with tracks from direct detection of other radiations in particular protons and low-energy light ions as well as X rays. This will limit the neutron-event discrimination in mixed-radiation fields. The detection response according sensor-mask region was examined and calibrated for the investigated neutron fields. The neutron detection efficiency is selectively derived for the detector particle-event classes. This approach enables to enhance the neutron-discrimination and suppress background and unwanted events. This work enables to extend the response matrix of the detector for broad-type radiations to include neutrons both fast and thermal. The results serve to enhance the sensitivity and determine the neutron component in unknown and mixed-radiation fields such as outer space and particle radiotherapy environments.

Volume: 18
Article Number: P01003
DOI: https://doi.org/10.1088/1748-0221/18/01/P01003

Volume: 57
Issue: 2
Pages: 025018
DOI: Not available

Pages: 26-29
DOI: N/A

DOI: N/A

DOI: N/A