Palmtop particle telescopes based on MiniPIX TPX3

The miniaturized MiniPIX TPX3 radiation imaging detector is designed with a maximal emphasis on versatility. Several of these devices can be combined into a larger multi-detector system either next to each other (to cover larger are or wider solid angle) or in layers on top of each other.

This article focuses on the second option: the arrangement of the two detectors stacked in layers forming a Miniaturized Timepix3 particle telescope. Each layer consists of the single Timepix3 detector (256×256 pixels with a pitch of 55 µm) equipped with either Si or CdTe sensors of various thicknesses (up to 2 mm CdTe). Each TImepix3 pixel measures the energy deposited by particle and time of arrival (1.5 ns precision).

The combination of Silicon and thick CdTe layer can be advantageous for the construction of a Compton camera optimized for low energies of gamma rays. Modules are internally synchronized: They use the clock frequency and shutter signal derived from one common master.

(Picture shows my colleagues Daniel and Daniela testing the telescope)

Both modules are connected to the DAQ computer(s) each via their own USB2.0 Micro-B connector. The USB hub can be used to aggregate these two lines. The power consumption of the whole device is 2.6 W.

Motivation and applications

This work was motivated by applications in space for monitoring cosmic rays (so-called space weather). The development is performed in tight collaboration with several partners including ESA and NASA.

There are several additional application fields:

  • Energetic hadron beams (e.g. for hadron therapy): Monitoring of secondary radiation (monitoring of treatment procedure).
  • Fast/slow neutrons with background suppression: The neutron converter can be interlaced between layers the anti-coincidence technique is used to separate proton background from neutron signal.
  • Observation of rare decay modes (detectors in face-to-face geometry).
  • Double layer Compton camera for gamma rays.

Fig. 1. The measured directional distribution can be visualized using such spherical mapping. The logarithmic intensity (flux) is shown as color.

History of Timepix based particle telescopes

The first telescopes were built and tested by a team of IEAP CTU in Prague in 2010 (article published in 2011) the second configuration (called ModuPIX) was created by the same team in 2013 (published 2014). ADVACAM company continued this development introducing ModuPIX Tracker and WidePIX 3D.

The overview of these detectors is shown here:

The AdvaPIX Tracker was developed for NASA and sent to ISS for radiation monitoring as described in this article by Dr. Jan Jakubek.

The WidePIX 3D is a very unique detector with 4 sensor layers in very tight contact. The Timepix readout chip is thinned down to 100 um so that the distance of sensitive layers is 250 um only. The example of measured tracks of particles in the normal environment of my office is shown here (please zoom in and look at delta electron recoiled by muon):

Example: Monitoring of Hadron Therapy

The Timepix3 detector provides very complete information for each ionizing particle passing the sensor: It gives an image of the particle trace. Each pixel of such image records the energy deposited and time of arrival. Different particle types create very different track shapes as illustrated in this article by Dr. Jan Jakubek or the picture below.

Fig.2. Various particle tracks recorded during the experiment with a therapeutic ion beam (amplitude corresponds to deposited energy). From left to right: Carbon ion track (430 MeV/u) at 80 degrees, proton track (200 MeV), scattered proton, recoiled nucleus, proton track with delta electron, fragmentation of carbon ion after collision with silicon, electron tracks, X-rays.

The 2D track shape images are very “information-rich” but for more precise measurement of angular distribution, it doesn’t give good data for particles entering the detector almost perpendicularly. In such a case, an arrangement with two (or more) detector planes above each other gives much better results.

Fig.3. Illustrative measurement with a stack of two Timepix detectors recording tracks of secondary particles induced by primary pencil beam of Carbon ions (430 MeV/u) penetrating: beam-exit window, air, thin plastic foil, and being absorbed in the water tank. The particle tracks recorded by both detector planes in coincidence were back-projected to the space revealing all components of the beam path including thin plastic foil. The production of secondary particles (mostly protons) depends on material density. The beam-exit to detector distance was 1.2 m.

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