Cosmic Ray Induced Ionization atmospheric measurements, calibrations and image pattern recognition by the Medipix detectors

Field: Physics and Astronomy (Physical Sciences)

This thesis project is based on the data analysis and interpretation of Cosmic Ray Induced Ionization (CRII) radiation environment measurements acquired during author-designed experiments “Timepix@Space“ and “CRIndIons“ on BEXUS-7 and on BEXUS-9 stratospheric balloon campaigns resp. In the thesis, results of the first two experiments using the semiconductor pixel detectors of the Medipix family for energetic particle imaging in the stratospheric environment are presented. The original detecting device was based on the hybrid pixel detectors of Medipix-2 and Timepix developed at CERN with USB interface developed at Institute of Experimental and Applied Physics of Czech Technical University in Prague. The detectors were used in tracking mode allowing them to operate as an "active nuclear emulsion". The actual flight time of BEXUS-7 with Medipix-2 on 8th October 2008 was over 4 hours, with 2 hours at stable floating altitude of 26km. BEXUS-9 measurements of 3.5 hour duration by Timepix, Medipix-2 and ST-6 Geiger telescope instruments took place in arctic atmosphere till ceiling altitude of 24km on 11th October 2009. Stratospheric balloon platform is the optimal realization for such in-situ measurements of atmospheric ionization. Optimal not only because of the high altitudes reached, but also due to its slow ascent velocity for statistically relevant sampling of the ambient environment for improving cosmic ray induced ionisation rate model inputs. The flight opportunity for BEXUS student projects was provided by Education department of the European Space Agency (ESA) and Eurolaunch - Collaboration of Swedish National Space Board (SNSB) and German Space Agency (DLR). The scientic goal was to check energetic particle type altitudinal dependencies, simultaneously testing proper detector calibration by detecting fluxes of ionizing radiation while evaluating instrumentation endurance and performance. Extensive dataset of different types of cosmic ray particle image tracks were acquired in the stratospheric radiation environment, sorted and analyzed. Terrestrial Cosmic Ray Flux (CR) is considered by the scientific community as a possible important agent influencing various atmospheric phenomena that range from Global Atmospheric Electric Circuit, dust concentrations, to cloud properties. Therefore, better experimental data on specific atmospheric fluxes along with particle types and energies present are an important input into various models. According to many scientists it will be very important to develop fully automatic, small, and light CR stations for regular ship and aircraft lines for continuous planetary surveys. Such an extended network of both stationary and moving CR stations will be much more effective also for problems related to space situational awareness and space weather (e.g., forecasting of dangerous magnetic storms by analyzing galactic CR distribution and great radiation hazards from solar CRs). Therefore we argue that such a CR station could be readily available in low- cost setup, providing all the required measurements. The feasibility study for gaining actual improvement of CRII estimation from the induced ionization measurements in silicon is undergoing, expecting to provide better atmospheric altitudinal spectra of particle types and energies, improving overall CRII model simulations. Detector performance is evaluated for further design implications of advanced concepts focusing on Cosmic Ray Induced Ionization rate measurements. General comparison of the project results with relevant simulations from OuluCRAC, GEANT4 and CORSIKA are presented. Reproducible laboratory measurements of artificial emitters and respective calibrations were undertaken with goal of optimizing the algorithms of ionizing radiation pattern recognition to represent the track patterns as realistic components of unknown (mixed) radiation field. This was undertaken under supervisory of Jan Jakubek, PhD, from IEAP CTU in Prague in scope of the CERN Medipix Collaboration.