Cosmic radiation measurements in the southern hemisphere, with the focus on aviation altitudes

PhD (Space Physics), North-West University, Potchefstroom Campus

The radiation environment around the Earth is intense and complex. During the dawn of the aviation age in 1903, when the Wright brothers Orville and Wilbur invented, built, and flew the world’s first successful aircraft, little was known about atmospheric radiation and its dependence on altitude. In early 1912 Victor Hess discovered that cosmic-ray intensity increases with altitude. The radiation field at and above aviation altitudes differs significantly from the radiation environment on Earth’s surface. On the Earth’s surface it is dominated by terrestrial radiation which stems from radionuclides in the Earth’s crust and secondary by-products produced by cosmic-rays interaction with the Earth’s atmosphere. In the atmosphere, the radiation field consists of a complex mixture of charged and neutral secondary particles. However, above the atmosphere, primary galactic cosmic-rays, particles from the Sun, and from the radiation belts around Earth, play a significant role. Hence, the radiation exposure is high at and above the atmosphere, especially over the poles and the South Atlantic Anomaly, because of the orientation of the Earth’s geomagnetic field lines. The study of cosmic-ray interaction with the atmosphere is of great importance; such a study can address the essential science concerning long-term human space exploration risks and aviation radiation exposure for flight personnel and passengers. Most important is how the future of aviation is threatened by these increasing levels of radiation at and above the atmosphere. Given that, in the atmosphere, radiation is very high during solar minimum and low during solar maximum conditions (transient solar events can potentially increase atmospheric radiation even during this solar period), measuring radiation levels during these periods both in the atmosphere and on the Earth’s surface is absolutely essential. This is also important in the Southern Hemisphere, where little or no such information is available at present. In this thesis, a portable active dosimetry device based on two silicon semiconductor diodes is assembled, tested, and calibrated. This dosimeter is used to study the dose rate distributions from mid to low latitudes at various altitudes. Field tests on board commercial aircraft within the mixed radiation field at aviation altitudes are successfully performed and important dosimetric quantities calculated. Investigations on whether models currently used to analyze (or predict) radiation exposure of flight personnel are satisfactory will also be discussed and compared to measurements. As part of the public awareness, a campaign initiated by the North-West University’s Centre for Space Research in 2017, a battery powered detector known as HARM is used to monitor atmospheric radiation evolution with altitude from ground-level to aviation altitudes in commercial aircraft or higher altitudes (in principle up to a residual atmosphere of about 2:83 g=cm2, i.e. - 40 km) by means of launching balloons.

Doctoral