Answer to Question #3509 Submitted to "Ask the Experts"

There has been a fair bit of research on this topic but I am unaware of a single comprehensive article covering this subject. That doesn't mean that there is no such article however. One problem is that this is as much an astrophysics question as it is a health physics question—neutron exposures are insignificant until we get to high altitudes.

Assuming that you have easy access to the health physics literature, let me suggest a search of abstracts in the following journals:

• Health Physics
• Radiation Protection Dosimetry

For search words, you could try cosmic, neutrons, latitudes, or altitudes.

Unfortunately, the information in the National Council on Radiation Protection and Measurements (NCRP) Report 94 "Exposure of the Population in the United States and Canada from Natural Background Radiation" seems to be limited to the variation in neutron flux with altitude. Nevertheless, there are a few references in there that might prove helpful.

One reference that I would recommend that you track down is "Radiation Environment in the Stratosphere" by G. Reitz in Radiation Protection Dosimetry 48:5-20; 1993. Needless to say, this is another source of references.

Others are:

• Korff et al. Cosmic ray fast neutron flux measurements in the atmosphere at various latitudes. Canadian Journal of Physics 46:S1023-S1026; 1968.
   
• Chupp EL. Annual review of astronomy and astrophysics 22:359; 1984.
   
• Hewett et al. Exposure to cosmic ray neutrons at commercial jet aircraft altitude. In: Natural Radiation Environment, Vol. 2:855-881. Proceedings of a symposium held at Houston, Texas, April 1978. U.S. Department of Energy Report CONF-780422, Washington, DC; 1980.
   
• McAulay IR. Radiation exposure of civil aircrew. Radiation Protection Dosimetry 48:1; 1993.
   
• Cosmic Radiation and Aircraft Crew Exposure. Radiation Protection Dosimetry 86:4; 1999.

Paul Frame, CHP, PhD