RE: Another question re: dose

[Jack_Earley@RL.GOV]

Richard Hess wrote:



<<One item caught my attention. Someone was trying to differentiate between

a whole-body dose (let's say 10mSv/year) and that same dose applied to a

single point (I think the example was within the lung).



I realize that an alpha emitter may create a much greater risk (why else is

its QF 20?) but I think I'm lost about whole body doses and point doses.



Now that I'm thinking about it, how do some things become contaminated with

radiation while others don't?>>

____________



If it was the same article I read most of, they were trying to differentiate

between whole body dose and the dose on a cellular level. Something like

"hundreds, thousands, millions of hits on these [poor] cells over weeks,

months, and years!" Of course, the author kind of forgot to mention that

these same cells receive millions of hits per day from background sources. .

. .



On whole body vs. point sources, though, it's still a matter of dose--the

difference is the insult to the organism vs. the organ. For example, if you

burn 90 percent of your hand, you'll survive although you may lose your

hand. If you burn 90 percent of your body, your survival chances shrink.

Depends on the dose, though--were those 1st, 2nd, or 3rd degree burns? High

doses are used to kill tumors--if applied to the body as a whole, you would

die from it. Same thing if you kill the wrong organ--you can be stabbed in

the stomach and survive, but unlikely if you're stabbed in the heart.



Radiation can't contaminate anything. Big media misunderstanding on the

concept here--I cringe anytime I hear a media report on radiation because I

know what's coming: "There was no leak of radiation." Radiation is energy;

if it "leaks," it's because there was an inadequate shield, e.g., only 1 in.

of shielding at one location instead of the 5 in. everywhere else. You can't

become contaminated from energy. Some things can be radioactive by being

activated from, e.g., neutron irradiation. In that case, the material would

absorb a neutron, changing its chemical form, such as from H-2 to H-3, and

since it now has more energy, it has to decay to a stable state. A general

definition of contamination is radioactive material somewhere you don't want

it to be. Fertilizer in your yard or stable is fine--not so good on your new

carpet. We don't consider a sealed source to be contaminated unless it leaks

to the outside. From there it can spread to anything with which it comes in

contact. It can fall off during transport and contaminate whatever it lands

on. The question then becomes, how much? We had a man injured inside the

reactor building at TMI some years ago. Checking the transport path after he

was taken to the ambulance, the area that was contaminated was where the

stretcher was placed, even though it had been covered with plastic before

the man was placed in it. But it had been on top of an emergency response

cabinet for years, and although the minute quantities of radioactive

material that landed on it from the air were all immeasurable, and well

below any limits, they built up over time to become measurable and above

limits, and therefore "contamination."



Jack Earley

Radiological Engineer





-----Original Message-----

From: Richard L. Hess [mailto:lists@richardhess.com]

Sent: Friday, September 06, 2002 2:35 PM

To: radsafe@list.vanderbilt.edu

Subject: Another question re: dose





A while ago someone posted an anti-nuke URL to this list. I went and read 

it and started seeing through all of the hoopla.



One item caught my attention. Someone was trying to differentiate between a 

whole-body dose (let's say 10mSv/year) and that same dose applied to a 

single point (I think the example was within the lung).



I realize that an alpha emitter may create a much greater risk (why else is 

its QF 20?) but I think I'm lost about whole body doses and point doses.



Now that I'm thinking about it, how do some things become contaminated with 

radiation while others don't?



Pointers to GOOD FAQs would be useful (it's hard to separate wheat from 

chaff in this subject on the Web).



A little math doesn't scare me...but lots of math does <smile>.



Thanks!



Richard



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