The Mobile Dosimetric Telescope - A Small Active Dosimeter for the Application in Space – Development, Calibration and Measurements –

Abstract

The radiation field in low Earth orbit (LEO) and at aviation altitudes differs significantly from the radiation environment on Earth’s surface. On ground it is dominated by radioactive decay products as well as by secondary particles produced by cosmic radition in the atmosphere. At aviation altitudes the radiation field consists of a complex mixture of charged and neutral secondary particles, whereas further out, e.g. in LEO at the altitude of the International Space Station, primary galactic cosmic radiation, particles from the sun and from the radiation belts around Earth play a significant role. This makes the radiation exposure one of the main hazards for the health of humans in space and poses a limiting factor for long duration space flights. Hence it is essential to continuously monitor the radiation exposure of astronauts, which is currently conducted with passive personal dosimeters and active area monitors onboard the International Space Station. Portable active devices, which can be worn by the astronaut all the time, are however desirable. In the course of this thesis a prototype for such a small size battery driven active personal dosimeter based on silicon detector technology is developed and its working principle is verified. The electronics is designed to match the requirements of the complex radiation field in LEO. The dosimeter measures absorbed dose and dose rates and includes a real time display as well as a micro SD card for data storage. The detector system is based on two silicon diodes arranged in a telescope configuration. The absorbed dose is obtained by considering all particles measured in either of the detectors. Particles traversing both diodes are recognized as coincidence events and enable to derive linear energy transfer spectra from which the quality factor of the radiation field can be determined. The quality factor gives information on the biological effectiveness of the radiation. With the information of absorbed dose and quality factor the dose equivalent can be estimated. In the frame of this thesis two prototypes of the Mobile Dosimetric Telescope (MDT), MDT-01-000-DLR-CAU and MDT-01-001-DLR-CAU, are developed, comprising the same electronics in different housing and their working principle is presented. The detectors are characterized and calibrated with radioactive isotope sources and heavy ions. They are intensely tested in fragmentation measurements of heavy ions proving excellent detection capabilities of densely ionizing heavy ions. Field tests onboard aircraft within the mixed radiation field at aviation altitudes are successfully performed and important dose quantities and physical parameters of the radiation field are derived. Furthermore basic simulations show the applicability of the MDT in space.