RE: Question on low-dose rad effects

["Tom Morgan" <tmorgan@isotopeproducts.com>]

Two thoughts come to mind and I am sure that readers of this list will
provide others:

1. Limitations of our current dosimetry system

Radiation workers wear personal dosimetry systems on the job.  Whether they
wear a film badge or a TLD badge, their dose is reported in mrem.  That is,
an estimate is made of the amount of radiation energy absorbed by the very
small mass of the sensitive part of the badge.  For simplicity, it is
assumed (incorrectly, of course) that whatever dose is recorded on this
badge is representative of a uniform radiation field and that this, in turn,
is representative of the worker's exposure.

Obviously, radiation fields are rarely uniform.  Consequently, the radiation
worker's exposure will vary from point to point over his or her body.  I am
sure that the variation is easily greater than a factor of two.  In other
words, the nonuniformity of probably overshadows any variation in mass from
one worker to the next.

2. Inaccuracy of risk estimates at low doses.

For all the research that has been conducted and published on the low level
effects of ionizing radiation, the derived risk estimates are not accurate
to better than a factor of two at occupational levels.

Therefore, using the statistical propagation of error formulae, it is clear
(from this hand waving argument) that the uncertainties mentioned above (and
others) swamp out the effects of even a two-fold mass variation between
workers.


Thomas L. Morgan, Ph.D.
Director of Health Physics
Radiation Safety Officer
Isotope Products Laboratories
1800 N. Keystone Street
Burbank, CA 91504
818-558-1375 (voice)
818-843-6168 (fax)
tmorgan@isotopeproducts.com



 -----Original Message-----
From: 	radsafe@romulus.ehs.uiuc.edu [mailto:radsafe@romulus.ehs.uiuc.edu]
On Behalf Of Jerry Cohen
Sent:	Thursday, October 12, 2000 3:27 PM
To:	Multiple recipients of list
Subject:	Fw: Question on low-dose rad effects





     Perhaps someone could enlighten me on something that has puzzled me for
a long time. Why is the degree of harm, detriment, etc. from low-level
radiation  expressed in terms of rad, rem, sieverts, etc. which are
functions of absorbed energy per unit mass (i.e. ergs/gm)?
 Isn't the probability of a mutation, or other adverse effect a direct
function of the total number of ionizing events occuring in the vicinity of
suseptible DNA molecules and isn't that ,in turn, a function only of total
absorbed energy?
     For example, consider two individuals of the same age, sex, and general
state of health with the only difference between the two being that one
weighs twice as much as the other.  Given that both recieve a radiation dose
of say 1.0 rem, have they both experienced an equal degree of harm? Due to
his/her larger mass, the heavier individual gets twice as many ionizing
events occuring near twice as many DNA molecules any one of which might
result in an adverse mutation.  Why doesn't the individual with twice the
mass, get twice the risk???     Jerry Cohen
jjcohen@prodigy.net

>
>

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