Purpose: Nanodosimetry uses physical quantities based on ionization cluster size distributions to model the biological effectiveness of different radiation qualities. A nanodosimetric detector in operation is the FIRE (Frequency of Ion Registration) detector, but further design optimization of the detector is required. The electrostatic simulations presented in this work will help guide future developments of the detector.
Methods: Within the FIRE detector, the produced ions drift towards a dielectric plate hole, within which they are strongly accelerated towards the cathode and produce an electron avalanche through impact ionization. The electron avalanche is measured at the signal readout. COMSOL Multiphysics was used to calculate the electrostatic fields and Garfield＋＋ was used to simulate ion drift trajectories and electron avalanche formation employing Monte Carlo methods.
Results: The dependency of electron avalanche formation on experimental parameters, such as pressure or electric field configuration, was studied and compared to experimental results. Based on the funneling effect ions experience within the drift region, a calculation method for obtaining an optimized hole pitch for future multi-hole detector designs was presented.
Conclusion: The results presented in this work offer valuable insights into the inner workings of the FIRE detector, as well as clarify how different experimental parameters influence signal creation.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the Swiss Federal Nuclear Safety Inspectorate (ENSI, contract CRT00512).
Monte Carlo, Modeling, Dosimetry
TH- External Beam- Particle/high LET therapy: Carbon ion therapy – experimental dosimetry