The following question came up during our Radiation Protection Class. "If a pilot was to fly a night would this reduce the amount of radiation that the pilot and crew would be exposed to?" In my search to answer this question I contacted Richard Brey, a Professor of Physics at the Idaho State University and this was his reply.

Ben,

To answer your question directly; no, there is little anticipated difference in the ionizing radiation exposure received during the day or at night. Very little of the cosmic ionizing radiation exposure received by humans is associated with solar radiation. Although our sun does produce ionizing radiation that source of ionizing radiation is greatly deflected by the Van Allen Belt which surrounds the earth. The Van Allen radiation belt is a torus of energetic charged particles (plasma) around Earth, which is held in place by Earth's magnetic field. Cosmic radiation exposure on the surface of the planet is related to extremely high energy particles and waves generated by other stars in our universe. This radiation sometimes serves as a source of direct exposure, and it frequently generates secondary radiation when it interacts in the earth's atmosphere. Some of the radiation exposure we receive is associated with the secondary particles generated by spallation reactions in the atmosphere. Some of the exposure is associated with the so called cosmogenically produced radioactive material such as C-14, H-3, and Be-7. A good reference on this subject is NCRP Report No. 160 which was published in 2009 and is entitled Ionizing Radiation Exposure of the Population of the United States (ISBN : 978-0-929600-98-7). This may be purchased on-line from NCRP (The National on Radiation Protection and Measurements). The NCRP web-page may be found at: http://www.ncrponline.org/. To find a copy of the report described above simply click on the Publications tab. I hope this is helpful.

Richard Brey, Ph.D., C.H.P.
Professor of Physics
Director, ISU Health Physics Program