Re: dose calc

[avest@magnus.acs.ohio-state.edu (Albert Lee Vest)]

Welcome, Mr. Williams.

>A Dr. Howard Vogel told me recently that an experiment he did in Oak Ridge 
several years ago showed that exposure of rats over a long period of time caused
>much higher rates of mammary cancer than the same exposure over a short period.
>He says this is the opposite of what is known to occur with gamma ray 
>exposures.

Quite the contrary.  For "low doses," delivery at a higher rate seems to 
correlate with fewer effects.  This is the well-known "Rate Effect."  See 
Herman Cember's "Introduction to Health Physics" - I wish I could refer you 
to the chapter/section, but someone is borrowing my copy right now.  I 
believe it is also discussed in various BEIR, ICRP, and NCRP reports.

>I thought a rem was a rem. If not what good is this method of calculating the
>biological damage done to an organism?

Fortunately, unless you're a medical physicist (as opposed to a health 
physicist), you don't have to quantify tissue damage.  Even then, you do it 
in advance, rather than try to find out what happened after the fact.

But what *we* have to do is measure and catalog occupational (and, in some 
cases, public) radiation dose-equivalents, after they have happened.  We 
don't concern ourselves with radiation effects *on individuals*, because at 
or below the legal dose limits they can't be measured *in individuals*.  But 
dose and dose-equivalent can be.

For neutrons, we have to apply a "quality factor" to account for different 
LET rates at different energies. (these also apply to alphas and other 
high-energy particles, but we don't deal very often with those).  This 
dependence on particle energy is not bothersome, because particle energy can 
be measured, and doesn't change from one experiment to another.  We can 
still "keep score" on a worker.

What if we also, by law, had to apply a "rate factor", similar to a quality 
factor, to our radiation surveys and dosimetry measurements?  Has a TLD been 
invented that not only records the dose received, but at what rate it was 
received?  Should we assume the dose was received uniformly over the badge 
period, even though it all may have been deposited in a few seconds?  And 
"how long was it -- 5 seconds or 15 seconds?" -- I ask people enough silly 
questions as it is!

To the best of my knowledge, NCRP has not recommended adopting any "rate 
factor" for radiation worker dosimetry other than 1.0.  Maybe the better 
HP's on the list (I'm certainly not among them) will bring you up to date.
Albert Lee Vest    avest@magnus.acs.ohio-state.edu
health physicist        Office of Radiation Safety
(614)292-0122            The Ohio State University
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