Speaker
Description
Due to their ability to track single particles and measure energy deposition,Timepix detectors are successfully used for various research projects in particle therapy. Examples include the helium-beam radiography project or the estimation of LET spectra for ion radiation fields at the German Cancer Research Center (DKFZ) and the Heidelberg Ion-Beam Therapy Center (HIT) in Heidelberg, Germany. Some of these projects are advancing towards clinical applications. Using Timepix detectors in clinics requires a stable and reliable performance over a long time. After multiple exposures to ion radiation, an unexpected pattern of cluster shapes was observed in Timepix3 data at DKFZ.In this context, potential radiation damage due to ions was investigated. Since different kinds of ions were used for the experiments especially the comparison between protons and oxygen ions was of interest.
To investigate the radiation damage in clinical ion beams, two Timepix3 detectors were irradiated in a stepwise manner, one with oxygen ions and one with protons at HIT in Germany. After each step, a control measurement with helium ions at moderate fluence rates of 10^4 to 10^5 ions per second per active area was taken. Due to a saturation effect in Timepix3 at high LET events, these measurements were done with a partially depleted sensor. To test the radiation damage in the sensor, cluster size and the cluster energy from the control measurement with helium ions were investigated after each step of the high-intensity irradiation with protons and oxygen ions.
Two counteracting effects make it challenging to derive accurate and precise quantitative statements about the sensor’s response. Hadronic radiation is known to produce defects in the crystalline structure of the sensor, which can lead to charge trapping reducing the collected charge. On the other hand, radiation damage can lead to an extension of the depletion depth in the sensor. However, for the time being, it is our understanding that none of the original unexpected patterns seem to be related to radiation damage. Nevertheless, radiation damage could alter the detector’s response. Therefore, when using a Timepix3 detector in future experiments with ion beams care has to been taken to these effects.
| Workshop topics | Applications |
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