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