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Description
Timepix3 [1] is a hybrid pixel detector with $55\,\mu\mathrm{m}$ pixel pitch in a matrix $256 \times 256$ pixels. It can measure in data-driven mode when it detects both the deposited energy and time of arrival (ToA) in the pixels. The ToA is written with $1.56\,\mathrm{ns}$ precision. The fine ToA resolution permits 3D reconstruction of tracks within the sensor [2]. This makes Compton camera imaging possible.
The reference [3] evaluates a single Timepix3 detector with a 1 mm thick silicon sensor for the use as a Compton scatter polarimeter, relying on the detection of coincident Compton scattering and photoabsorption. The evaluated energy range was $30\!-\!220\,\mathrm{keV}$ in simulation and $32.5\!-\!67.5\,\mathrm{keV}$ in a laboratory experiment. It was shown that the detector offers a maximum modulation factor $\mu_{100} > 77\,\%$ in the energy range $45\!-\!80\,\mathrm{keV}$. However, a single detector is limited by its low efficiency of detection of the two coincident events, with $\varepsilon = 0.13\,\%$ being its peak value. The quality factor $q = \mu_{100} \sqrt{\varepsilon}$ reached its maximum $q = 2.9\,\%$ around the photon energy $50\,\mathrm{keV}$.
The Compton camera imaging of the X-ray source is also evaluated in the reference [3]. The reconstruction method used was origin ensemble with resolution recovery (OE-RR). This is a Monte Carlo Markov chain method that tries to maximize the image likelihood function by stochastically updating photon origins one by one until it reaches a dynamic equilibrium. The full width at half maximum of the image $16\!-\!21^\circ$ was achieved.
In this work, we will present the simulations of combining multiple Timepix3 detectors to enhance the efficiency of detection. The basic setup consists of 4 silicon Timepix3 detectors stacked behind each other with 4 cadmium telluride Timepix3 detectors around them to boost the detection efficiency of perpendicularly scattered photons. Using this setup of 8 Timepix3 detectors, the quality factor monotonically increases from $2.9\,\%$ at $35\,\mathrm{keV}$ to $10.6\,\%$ at $65\,\mathrm{keV}$. If we use two such setups together with 16 detectors in total, the quality factor monotonically increases from $3.9\,\%$ at $35\,\mathrm{keV}$ to $14.0\,\%$ at $65\,\mathrm{keV}$.
Fine pixelization of Timepix3 detector would also enable imaging of the X-ray sources. A stack of Timepix3 detectors could be placed in the focal plane of an X-ray mirror, or it could take images using the Compton camera principle. Given the rich space heritage of Timepix-family detectors [4], Timepix3 could be used in some of the future X-ray polarimetric missions. The new detector Timepix4 with a larger area and better time resolution could be even more promising.
[1] Poikela, T. et al. "Timepix3: a 65K channel hybrid pixel readout chip with simultaneous ToA/ToT and sparse readout", JINST, 2014
[2] Bergmann, B. et al. "3D track reconstruction capability of a silicon hybrid active pixel detector", The Eur. Phys. Jour. C, 2017
[3] Jelinek, J. et al. "Evaluation of Timepix3 with a 1 mm thick silicon sensor as a Compton imaging polarimeter in the hard X-ray band", JINST, 2025.
[4] Bergmann, B. et al. "Results and Perspectives of Timepix Detectors in Space—From Radiation Monitoring in Low Earth Orbit to Astroparticle Physics", Instruments, 2024
| Eligibility for "Best presentation for young researcher" or "Best poster for young researcher" prize | Yes |
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