Landroger:
The Inverse Square Law isn't relevant for radiation from the sun, since the distance from the sun doesn't change significantly whether you're at 60,000 feet or sea level... of course if dealing with muon showers initiated in the upper atmosphere, it's different. In any case the ISL only holds in the absence of absorption, if absorption is present the radiation will decay faster than inverse square. So "12 feet better than 8" is always true, but not necessarily because of the ISL.
Regarding the TLD's and cosmic rays, I came across this
link. I didn't read the paper but the abstract says it all:
The response of LiF thermoluminescence dosimeters to the ground-level cosmic-ray background
This article is not included in your organization's subscription. However, you may be able to
access this article under your organization's agreement with Elsevier.
Keran O'Briena
aEnvironmental Measurements Laboratory, U.S. Department of Energy, New York, NY 10014, U.S.A.
Received 7 December 1977;
accepted 21 February 1978.
Available online 3 October 2002.
Abstract
Monte-Carlo calculations of the response of LiF thermoluminescence dosimeters to cosmic radiation have been carried out and indicate that the dosimeter, when calibrated against gamma radiation in air, registers 0.83 of the muon-produced ionization. This is due both to the density effect and to the large proportion of muon-electron energy transfer that takes place when the cosmic-ray muons interact with the thermoluminescent material. The result is a systematic underestimate of the environmental radiation exposure rate of about 0.5 μR/hr.
The International Journal of Applied Radiation and Isotopes
Volume 29, Issue 12, December 1978, Pages 735-739