Abstract
The Miniaturized Detector for Application in Space (MIDAS) is a compact device with dimensions 5 × 5 × 1 cm3that combines position-sensitive Si detectors and a fast neutrons spectrometer. MIDAS is developed with the purpose of acting as a linear energy transfer (LET) spectrometer for the charged particles and measuring 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 LET∞in water from the measured LET has been elaborated. The dose rate in water and dose equivalent rate has 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.
Highlights
Segmented Si diode detectors are used in almost all the instruments measuring the mixed radiation fields of the space environment (Spence et al, 2010; Hassler et al, 2012; Rodríguez-Pacheco et al, 2020)
The dose equivalent is equal to the dose times the quality factor (Q), where Q is a function of the linear energy transfer (LET) – the rate of energy loss of a particle in water measured in keV lmÀ1
In the present paper, based on simulation experiments performed with the aid of the GEANT4 (GEometry ANd Tracking) package, we present a detailed study of the following subjects: (a) The reconstruction of the charged particle tracks using the energy deposition patterns on the pixel layers. (b) The calculation of the measured LET distribution. (c) The correction of the measured LET for the escaped energy and the determination of LET1 in water. (d) The calculation of the dose and dose equivalent rate using LET1 in water. (e) The response of Miniaturized Detector for Application in Space (MIDAS) inside a spacecraft model, where the galactic cosmic ray (GCR) radiation field is modified due to the interaction with the Al walls
Summary
Segmented Si diode detectors are used in almost all the instruments measuring the mixed radiation fields of the space environment (Spence et al, 2010; Hassler et al, 2012; Rodríguez-Pacheco et al, 2020). ESA required a device sensitive to both charged particles and neutrons to enable measurement of dose, dose rate, energy deposition, LET, and calculation of dose equivalent. 2022, 12, 8 tracks and the energy depositions from charged particles, we proposed to use MIDAS fully depleted monolithic active pixel sensors (DMAPS). The correct treatment of low-energy protons is important For this reason, the default GEANT4 model (Lassila-Perini & Urbán, 1995) for the calculation of energy depositions by charged particles was checked: in a simulation experiment, protons with 1244.1 MeV kinetic energy were impinging vertically on a fully depleted silicon slab with 51 lm thickness. This means that all the plastic scintillator cube facets are covered by at least one silicon layer, something which was not foreseen in the initial design of the device, as explained in Lambropoulos et al (2019). (c) In the calculations, only energy depositions above 20 keV are used as a conservative estimate of the pixel readout electronics sensitivity
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