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Standard radiation environment monitor: simulation and inner belt flux anisotropy investigation
2009 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The Standard Radiation Environment Monitor (SREM) is a standardised particle detector for mapping highly-energetic protons and electrons of the radiation field. It is employed on several ESA spacecraft (Integral, Rosetta, PROBA-1, Giove-B, Herschel, Planck) to provide radiation level information and to issue dose warnings to other instruments. A geometric model of the SREM instrument is simulated using GRAS/Geant4 to determine its directional response function. The instrument response to both protons and electrons is obtained for a wide range of discrete energy levels and directions of particle incidence. Analysis of the simulation output shows the directional characteristics of the SREM response and the resulting sensitivity to the pitch angle distribution of the flux. The directional, spherical and integrated response functions of the SREM are presented and discussed. The SREM on PROBA-1 (Project for On-Board Autonomy) gathers data of geomagnetically trapped protons, particularly in the South Atlantic Anomaly (SAA). The proton flux in the PROBA-1 orbit is investigated using the omnidirectional AP-8 model. Combining the SREM response function with the proton flux yields predictions of the SREM countrates which are then compared to data measured by PROBA-1. The influence of flux anisotropies on the SREM countrates is demonstrated and proves the necessity of including a model for the distribution of particle pitch angles: the Badhwar-Konradi model of pitch angle distribution is implemented and combined with the omnidirectional AP-8 model to yield an anisotropic unidirectional flux model. As a consequence, significant improvements to the AP-8 model are realised. The importance of considering flux anisotropies is shown both for short-term SREM countrate features and long-term integrated counts. Data analysis and comparison to simulated data is performed with respect to different values of McIlwain's L-coordinates and varying particle pitch angles. To simulate countrates, the attitude of the SREM on PROBA-1 relative to the magnetic field vector is determined using the magnetometer on-board PROBA-1. Radiation due to geomagnetically trapped protons contributes substantially to the overall radiation levels on the International Space Station (ISS). Based on the importance of the pitch angle distribution, the relevance of proton anisotropy for ISS dose levels is motivated.

Place, publisher, year, edition, pages
Keyword [en]
Technology, Anisotropy, AP-8, Inner Belt, PROBA-1, SREM
Keyword [sv]
URN: urn:nbn:se:ltu:diva-48253ISRN: LTU-PB-EX--09/063--SELocal ID: 5b865839-41ce-44fd-99ad-5418bc44a8abOAI: diva2:1021593
Subject / course
Student thesis, at least 30 credits
Educational program
Space Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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