Gamma/neutron separation in the Martian radiation environment
Year: 2012
Type: dissertation
Abstract: The Mars Science Laboratory is a NASA Mars-rover mission which was launched in November 2011, and will land on Mars in August 2012. One part of the rover is the Radiation Assessment Detector (RAD) which will measure a broad spectrum of energetic particles at the surface of Mars. The instrument consists of a silicon detector telescope stack followed by two scintillators which are enclosed by an anticoincidence. The high-Z cesium-iodide scintillator and the proton-rich plastic scintillator are used for detecting charged as well as neutral particles. In contrast to charged particles, neutral particles can pass the anti-coincidence without triggering a signal and can therefore be distinguished from charged particles. The cesium-iodide scintillator has a high sensitivity to gammas while the plastic scintillator has a high sensitivity to neutrons. However, since cesium-iodide is sensitive to neutrons just as plastic is sensitive to gammas as well, separating gammas and neutrons is a challenging task. The measurement of neutral particles is further complicated by the fact that neutral particles often deposit only a random fraction of their energy in a detector. Therefore, the spectra measured in the scintillators do not reflect the incoming particle spectra. The scope of this work is to provide methods to separate gamma and neutron measurements of the RAD instrument. In this context, a model was developed to calculate the propagation of solar energetic particles, which can induce an increase of the Martian neutral particle radiation. Based on maximum likelihood estimations, an inversion technique to calculate the unknown Martian neutral particle spectra from measurements and detector response function was developed. A detector response function was calculated with a detailed Monte-Carlo model. The inversion technique was evaluated for different models of underlying measurement statistics, validated with neutron beam calibration measurements and tested for artificial generated measurements of the Martian neutral particle spectra. The developed inversion techniques are applicable to a wide range of particle detectors and will be used for future evaluation of the RAD neutral particle measurements.
Author: Jan Köhler
Language: English
Subfield: Radiation
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2275352223