Re: Mice and elephants

[Bernard L Cohen <blc+@pitt.edu>]

On Sun, 6 Jul 1997 Ccja@aol.com wrote:
> In re the question of the radiobiological equivalencies of exposure: in
> health physics, for the purposes of routine protection of persons (in
> contrast to, let's say, basic research into dosimetry) the value most
> commonly used, where exposure to penetrating external radiation is the
> concern, is the deep dose equivalent (DDE). That is, the dose equivalent at a
> depth of 1 gram/sq.cm. (i.e., 1 cm.) in soft tissue, starting at the exterior
> of the body. This is merely a convenient indexing point. Most of the organs
> which we are really protecting, e.g., the lungs, thyroid, female gonads, red
> bone marrow, etc., are at much greater depths, and sometimes pretty well
> shielded (RBM). Even the male gonads are well shielded, in the lateral view.
> Also, occupationally exposed individuals, and the general public, are not
> usually exposed to, for instance, the direct beam of a medical linac, in
> which electronic equilibrium may not be achieved before a depth of several
> centimeters.
> 
> So, I would think that a sumo wrestler (or an elephant), would receive less
> "real" exposure, if the DDE is the measure of said exposure, than a jockey,
> or, more to the point, a small child (or a mouse), for the same reason that
> fetuses receive rather less exposure than the expectant (or unknowing)
> mother, in most cases.
> 
> chris alston
> ccja@aol.com
> 
	For gamma rays and neutrons, the attenuation length is about 10-15
cm (depending on their energy) which makes shielding much less important
than Chris implies. For X-rays. of course, Chris has an excellent point.