Time-of-Flight Spectrometer

  Time-of-flight spectrometer Copyright: Medical physics group Setup of the time-of-flight spectrometer (Geant4 Simulation).

In cancer therapy with particle radiation most of the radiation dose deposited in the patient's tissue is caused by the well understood electromagnetic interaction. Nevertheless, nuclear reactions also contribute to the dose and especially produce characteristic features in the spectrum of secondary radiation. Unfortunately, nuclear reactions in the therapeutic energy range around 100 MeV are inadequately understood and their cross sections are known to a very limited accuracy. In most treatment plannings, which are preceding each patient irradiation, these reactions are not considered at all today. Therefore, our group is developing a time of flight spectrometer to measure the cross sections of carbon hydrogen reactions to an accuracy of 10% as a start. Later, this method could be used for other reactions.

The time of flight spectrometer measures fragments that originate from nuclear reaction in the target. This fragments have to be identified in order to reconstruct the underlying reaction. By counting the numbers of different reactions, their cross sections can be calculated. Time of flight, energy loss and kinetic energy are measured to identify each fragment by it's mass and nuclear charge numbers.

Scintillation detectors read out by photodiodes or silicon photomultipliers (SiPMs) are used for that purpose. These detectors are developed at our institute in cooperation with out workshops. At the same time, the whole design of the time of flight spectrometer is simulated in Geant4 in order to model the detector and compare experimental results to simulation.