3D reconstruction of particle tracks in a 2 mm thick CdTe hybrid pixel detector

Abstract

We demonstrate how the latest generation of hybrid pixel detectors of the Timepix family can be used to reconstruct 3 dimensional particle tracks on a microscopic scale, additionally determining the stopping power along the particles' paths. In an experiment, a Timepix3 detector with a 2 mm thick planar CdTe sensor was irradiated in a 40 GeV/c pion beam and used in a similar way to a time-projection chamber: The coordinates x and y were given by the trajectory projection (pixel pitch: 55 µm), the z-coordinate was reconstructed from the charge carrier drift time measurement (time binning: 1.5625 ns). The achievable z-resolution was studied at different bias voltages. Systematic inaccuracies due to an imprecise drift time model were determined and separated from the intrinsic uncertainty given by the time resolution. It was shown that a z-resolution of 60 µm could be achieved by a perfect modeling of the drift time. With the presented z-reconstruction methodology, we studied the charge collection efficiency as a function of interaction depth, which was then used to apply a charge loss correction to the per-pixel energy measurements. 3D event displays of pion, muon and electron tracks are shown.

Timepix3 as solid-state time-projection chamber in particle and nuclear physics

“…The ToA is measured with a precision of 1.56 ns. The necessary energy calibration and time-walk correction methodology is described in [6] and [1,2], respectively.…”

“…Timepix3 as a solid-state time-projection chamber in particle and nuclear physics voltage. Using the known relation of the drift velocity as a function of the electric field, the drift time dependence on interaction depth can be determined analytically for silicon [2] or numerically for CdTe sensors [1]. It was found that a -resolution of~30 m and~60 m can be achieved in 500 m thick silicon and 2 mm thick CdTe sensors, respectively.…”

“…Hybrid pixel detectors (HPDs) enable noiseless detection and processing of individual particle events. It was shown that HPDs of Timepix3 technology can be regarded as solid-state Time-Projection-Chambers (TPCs) allowing 3D particle trajectory reconstruction together with the measurement of the energy left in the sensor material [1,2]. Compared to gasfilled TPCs, semiconductor TPCs offer an increased speed of operation and a~10 × lower energy needed to create free charge carriers.…”

“…While MoEDAL primarily relies on passive nuclear track detectors (NTDs) and paramagnetic trapping volumes, Timepix and Timepix3 detectors are installed at different locations to provide a real-time measurement of the radiation levels and means to decompose the radiation field. In the present work, the track reconstruction methodology from [1,2] is firstly applied to simulated data to model the angular detector response for Minimum Ionising Particles (MIPs). After MIPs are extracted from the mixed field data taken in MoEDAL the methodology is used to measure their directionality.…”

MoEDAL physics results and future plans

“…Each pixel of the innovative TimePix chip comprises a preamplifier, a discriminator with threshold adjustment, synchronisation logic and a 14-bit counter. The operation of TimePix in time-over-threshold mode allows a 3D mapping of the charge spreading effect in the whole volume of the silicon sensor, thus differentiating between different types of particles species from mixed radiation fields and measuring their energy deposition [10].…”