GEANT4 simulation study of the response of a miniature radiation detector in Galactic Cosmic Rays and inside a spacecraft.

The Miniaturized Detector for Application in Space (MIDAS) is a compact device with dimensions 5 x 5 x 1 cm 3 which combines position sensitive Si detectors and a fast neutrons spectrometer. MIDAS is developed with purpose to act as a linear energy transfer (LET) spectrometer for the charged particles and measure dose and dose equivalent from both charged particles and neutrons. It is based on fully depleted monolithic active Si pixel sensors for the charged track and energy deposition measurements, while a plastic scintillator read out by a silicon photomultiplier is used to determine energy depositions from fast neutrons. A simulation study of the detector response in galactic cosmic ray (GCR) radiation fields with the aid of GEANT4 has been performed. Energy depositions and hit pixel addresses have been used to reconstruct tracks and calculate LET spectra. A method to calculate  in water from the measured LET has been elaborated. Dose rate in water and dose equivalent rate have been calculated.  The energy and particle composition of the radiation field produced by the interaction of GCR with the Al walls of a spacecraft model has been determined and the response of MIDAS in this radiation field has been investigated.