Some words on dosimetry

["Ron L. Kathren" <rkathren@tricity.wsu.edu>]

Norm --

With all due respect, the problem is that you are trying to simplify a very
complex problem.  There is but one message.  Radiation dose (more correctly
in this case absorbed dose) is very simply the amount of energy deposited by
the ionizing radiation per unit mass of matter.  When a person is exposed to
radiation, not all cells or parts of the body receive the same dose -- the
dose, even for external beams is nonuniform.  Consider a chest x-ray; the
beam is limited to the torso, and so the legs and head and pelvis receive no
dose, while the torso receives the dose.  The side of the torso facing the
x-ray tube receives a higher dose than the other side as some of the energy
is absorbed as the x-ray beam passes through the body.

In the case of radioactive materials taken into the body, these irradiate
the tissues from within.  In the case of iodine-131, the iodine enters the
bloodstream and a portion is rather rapidly taken up by (ie deposited in)
the thyroid gland with the remainder excreted, largely via the urine.
Since the radioactivity is concentrated in the thyroid gland, this organ
receives the highest dose.  The value of KI is based on the fact that it
provides many, many fold more nonradioactive atoms of iodine for the thyroid
to choose from.  Since the thyroid is nonselective -- it doesn't care
whether it takes up a stable or radioactive atom of iodine -- and the
radioactive species are outnumber by trillions or more to one, very few
radioactive atoms of iodine get taken up.  KI is useful only for radioiodine
protection by this blocking action; it will do nothing to protect against
the external radiation.

Human radiation exposure is a combination of internal and external doses
delivered nonuniformly to different tissues and organs.  Because of this,
health physicists use various factors to evaluate the dose in terms of a
whole body dose -- the so called effective dose equivalent.  The above only
scratches the surface of a very complex question.  Meaning no offense, and
judging by your questions and discussion,  it would seem that you could
profit from gaining a better basic understanding of radiation science.
There are a number of excellent books written by reputable independent
scientific folks for the intelligent nonscientist  that can provide you with
the necessary background.  Both Peter Alexander and Eric Hall, a professor
at Columbia University, have written such books, and  the League of  Women
Voters has put together an excellent little book, "The Nuclear Waste
Primer".   I am sure that my RadSafe colleagues can suggest many more.

As I indicated to you in a private e-mail some time ago, I think it is
important to open a dialogue between the scientists and the public, and
especially those with concerns.  I continue to support you in your quest to
learn more about the hazards of radiation and radioactivity, and renew my
offer to assist you in this regard.  But I believe that your quest would be
greatly facilitated were you to first gain some additional elementary
background in the scientific area you are exploring, just as I, a scientist,
would need to do if I were attempting to understand your particular field of
history.   Then we could cut to the chase and skip all these piecemeal
explanations which serve to hinder the process of open dialogue.  As an
historian you may remember that when electricity was first being introduced,
many otherwise knowledgeable people -- even PhD's -- were afraid to unscrew
a light bulb for fear the electricity would leak out!   Clearly such folks
were ill prepared to discuss the hazards of electricity.

Ron Kathren
Professor Emeritus
College of Pharmacy
Washington State University

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