RE: Dose Rates vs. Altitude

["Heinmiller, Bruce" <heinmillerb@aecl.ca>]

Louie Tonry wrote:

> One time I flew from Germany to Tel Aviv.  I took a pressurized ion
> chamber
> with me to prevent damage in the non-pressurized hold of the plane.  On
> the
> tarmac, the exposure rate was about 35 uR/hr, at 36,000 ft, the exposure
> was
> about 180-200 uR/hr.  I was supprised at the difference but not about the
> radiation exposure.
> 
> 
The number that catches my attention is the 35-uR/h.  That's nominally 5
times higher than I'd expect, unless you were in a very-high-background area
of Germany or the instrument was sitting near a load of radiopharmaceutical
material such as Mo-99.  Just a hunch, but I'd guess the latter, assuming
the calibration is OK.

Exposure is defined only for photons, but of course the ion chamber will see
and register direct charged particles as well, but it's not clear to me how
to interpret this in terms of exposure.  What it largely misses, and is not
designed to measure, is a lot of neutrons.  At that altitude (11 000 m), I
believe nominally half of the dose equivalent is from neutrons.

Bruce Heinmiller CHP
heinmillerb@aecl.ca
>  
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