Answer: The term ‘cosmic rays’ refers to elementary particles (such as electrons and protons), nuclei (such as helium nuclei, or alpha particles), and electromagnetic radiation (x-rays and gamma rays), of extra-terrestrial origin. These cosmic ray particles are produced by high-energy events very distant from the Solar System, such as supernova explosions. They come from all directions in space. In space, the cosmic ray particles consist mainly of fast-moving light atomic nuclei – protons (~50%), alpha particles (~25%), carbon, nitrogen, and oxygen nuclei (~15%), and electrons ( <1%). In the depths of the Earth’s atmosphere the mix of particle types changes. This is because secondary particles – which include neutrons and muons – are created by interactions between the primary cosmic rays particles and the atoms of atmospheric gases. The secondary particles have lower energies than the primary particles, but they may be very numerous because many secondary particles can be created by a single primary.
Answer: On the surface of the Earth, we are exposed to the effects of naturally occurring radiation – including cosmic rays – all the time. We are exposed to the effects of radon gas, radioactive decay in rocks and soil, and the low-level radioactivity of the compounds that we ingest and that make up our body tissues. Cosmic rays make up about 20% of the natural exposure of a typical Canadian. Cosmic ray exposure varies because of several factors: geographic elevation, geomagnetic latitude, and the 11-year cycle of solar activity. Our bodies are adapted to repair the damaging effects of radiation through normal biological processes.
Answer: On the surface of the Earth, we are shielded from most of the effects of cosmic rays. The Earth’s magnetic field will deflect most low-energy cosmic rays. Of those that strike the upper atmosphere of the Earth, most will interact with the atoms of the atmosphere (mostly nitrogen and oxygen) and be scattered or absorbed. However, since aircrew are working at altitudes well above the Earth’s surface, they are less protected than a person on the ground.
Answer: There are three main variables that determine the dose that persons on an aircraft will receive on a given flight:
i) Aircraft at higher altitudes receive greater amounts of cosmic rays than at low altitudes.
ii) The geomagnetic latitude. The N and S polar regions are less shielded by the Earth’s magnetic field than regions near the equator.
iii) The solar activity level. The Sun’s activity varies over an 11-year cycle. When the Sun is active, it shields the inner Solar System. When the Sun is inactive, the Earth receives more cosmic radiation. The Sun’s activity level is described by the ‘heliocentric potential’. The higher the heliocentric potential, the more effective the Sun is in shielding the Earth from incident cosmic rays. The Sun is currently in a period of low activity, but will increase in activity over the next few years.
Answer: The dose from radiation that a person receives is measured in units of sieverts (Sv). The average Canadian receives about 2.6 millisieverts (or 0.0026 Sv) per year from normal natural, industrial, and medical sources. A typical medical x-ray, for example, generates a dose of about 0.01 to 0.1 millisieverts. A typical trans-Canadian flight (e.g. YUL to YVR) will generate a dose of about 35 microsieverts, or 0.000035 Sv. Thus, it would take over 75 such flights per year to generate a received dose that is roughly equivalent to the normal annual background dose.
Answer: While collecting data for every aircrew individual or for every flight could be done in principle, in practice it would be too expensive, too cumbersome, and unnecessary. The mixed radiation field at aircraft altitudes is well known as well as its cyclical variation. Therefore, if the flight profile (i.e. a complete sequence of waypoints and altitudes) is known, the received dose can be estimated to within a reasonable limit of uncertainty. Finally, the method of using periodic measurements to confirm the results of estimation code has been deemed acceptable for use with the National Dose Registry.
Answer: In x-ray procedures, x rays pass through the body to form pictures on film or on a computer or television monitor, which are viewed by a radiologist. If you have an x-ray test, it will be performed with a standard x-ray machine or with a more sophisticated x-ray machine called a CT or CAT scan machine.
In nuclear medicine procedures, a very small amount of radioactive material is inhaled, injected, or swallowed by the patient. If you have a nuclear medicine exam, a special camera will be used to detect energy given off by the radioactive material in your body and form a picture of your organs and their function on a computer monitor. A nuclear medicine physician views these pictures. The radioactive material typically disappears from your body within a few hours or days.
Answer: PCAire uses real-time satellite data to obtain information about solar flare activities and particle spectra. This information is used as an input for a transport code calculation to estimate the additional dose resulting from solar particle events at aircraft altitudes.
Answer: The standard units of effective dose are microsieverts (µSv). This unit is part of the international SI system of units. It takes into account the biological effectiveness of all types of absorbed radiation. It is the product of the absorbed dose (measured in SI units of grays (Gy)) and a dimensionless factor stipulated by the International Commission on Radiological Protection (ICRP) indicating the biological effects of the radiation. The average Canadian receives a dose of about 2,600 microsieverts per year. A millisievert (mSv) is 1,000 microsieverts and would be used for the accumulated annual dose, e.g. 2.6 mSv.
PCAire provides a full service cosmic radiation monitoring service to private, commercial, and military airlines. Individuals can calculate and track their own radiation dose here.