High Akltitude Neutron Fields

["H.B. Knowles" <hbknowls@ix.netcom.com>]

RadSafers:

The measurements I have recently seen presented indicate that at about
subsonic jetplane altitudes (30,000 ft.) dose rates UP TO 1 mrem/hr may be
expected, with more typical values of about 0.5 mrem/hr, This is for
mid-and high-magnetic latitudes (40 N to the pole), somewhat lower closer
to the equator. The high value quoted results from a solar flare. These can
appear in a matter of hours and are a particular problem for supersonic
aircraft, like the Concorde and some US and Russian clones now being
considered. The Concordes typically fly at 60,000 ft. and encounter neutron
radiation fields 2 to 3 times greater than those at subsonic altitudes.(
The peak of solar activity that follows the 11-year cycle is a minimum for
cosmic rays, since the solar activity is accompanied by greatly increased
solar magnetic fields which entrap the lower energy cosmic rays.) The
neutrons contribute 40 to 50% od the total dose rate, but I am not sure
which neutron quality factors are used to calculate this proportion. The
balace, considered mostly to be low LET radiation, is from gamma-rays,
muons protons and some pions, although I do not think the latter two are,
strictly, "low LET" radiations. Good data are in fact somewhat sparse,
although there is now increased experimental activity in this area. Induced
radioactivity would seem to be a minor problem compared to these particle
fluxes.

 
H.B. Knowles, PhD, Physics Consulting
4030 Hillcrest Rd, El Sobrante, CA 94803
Phone\Fax (510)758-5449
hbknowls@ix.netcom.com