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Bachelor thesis on determining the angle of incidence for radiation protection measurements via the Timepix3 pixel detector in cooperation with the Computer Graphics Lab at TU Braunschweig


With the aid of an imaging Timepix3 radiation detector, the angle of ionizing radiation incidence for photons was determined using the shadow cast by a specific mounted absorber set‑up. For data analysis, a stochastic particle filter algorithm was implemented that is able to quickly and efficiently calculate the angle of incidence from image data at very low dose values of only 480 nGy and to do so within less than 600 ms.

The quick detection and indication of the angle of incidence serves to improve dosimetric applications and to optimize radiation protection. In case of excessive radiation exposure, affected persons can be immediately warned and, where necessary, given the chance to evade exposure, change their position, or optimize the shielding.

The Timepix‑3 detector is a spatially resolving pixel detector developed at CERN with a sensor area of 196 mm². The sensor surface is divided into 65,536 pixels with a pixel pitch of 55 µm each. The two semiconductor elements of the hybrid detector (sensor and ASIC chip) are manufactured separately and then linked via bump bonds.

The absorber setup consists of eight steel pins with a diameter of 1.5 mm each that are fixed on a PMMA plate. This plate is positioned directly above the detector. The ionizing photon radiation is absorbed by the steel pins and the direction of radiation incidence is calculated using the specific shadow cast.

To analyze the measured image data, a C++ software library was implemented in cooperation with TU Braunschweig and optimized with regard to its processing speed. The software was modified to work with the available computer hardware resources in the form of integrated or dedicated graphic units. For this purpose, a particle filter was implemented as a kernel in OpenCL C [1].

Besides the described application for localizing radiation sources or detecting the spatial radiation distribution, the angle of incidence also has a direct influence on the dosimetric measurands relevant to radiation protection. The uncertainties in the dose determination at various angles of incidence can thus be reduced, especially for surface semiconductor detectors. In many cases, this reduction is necessary for complying with the PTB requirements placed on dosemeters.

 Image file of the detected and calculated steel pin shadow positions (left) and detector housing (right).

Figure: Left: The detected and calculated steel pin shadow positions are highlighted in red. Right: Detector housing with filters.


[1]   Lehner, Felix; Roth, Jürgen; Hupe, Oliver; et. al.
Method for fast determination of the angle of ionizing radiation incidence from data measured by a Timepix3 detector.
Journal of Sensors and Sensor Systems, 10 (2021), 63-70, https://doi.org/10.5194/jsss-10-63-2021


J. Roth, Fachbereich 6.3, Arbeitsgruppe 6.35

O. Hupe, Fachbereich 6.3

F. Lehner, Fachbereich 6.3, Arbeitsgruppe 6.35