Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!hpfcdc!hpfcmgw!ron
From: ron@hpfcmgw.HP.COM (Ron Miller)
Newsgroups: sci.electronics
Subject: Re: Radiation Detectors/Counters
Message-ID: <1240005@hpfcmgw.HP.COM>
Date: 27 Apr 89 14:40:15 GMT
References: <5499@lynx.UUCP>
Organization: HP Fort Collins, CO
Lines: 65

> 
> How exactly is a "roentgen" defined? Is it in terms of energy dose, or just
> in terms of "counts" (ie, gamma striks regardless of energy, also do
> beta/alpha strikes count, even though they are obviously not as bad as
> high-energy gammas)? What is considered normal "background radiation" in
> roentgens?

REM is Roentgen Equivalent Man which is a correction factor for health
affecting dosage. For example, if you were a worker in a plutonium handling
facility, your exposure to gammas would be predictable via a Roentgen
measuring device and the exposure calculated by a correction factor for
the known energy of the gammas from Pu. (if any, I don't have references
handy) Nuclear powerplants utilize enough dosimeters that the correction
factor is already scaled in and many of the personal dosimeters read in
REM.

BTW, the Federal limit for exposure for Radiation Workers is 5 REM per 
year accumulation. The maximum allowable for lifetime dosage is
5 REM per year for every year of age over 18. Extremely localized body
parts have their own limits but 5 REM is the whole-body allowed dosage.
(Hands and fingers have higher limits because the risk to bone marrow
and blood producing organs is reduced.)

Alpha strikes in a G-M detection are non-events. The particle can't 
get into the tube!

Beta can be screened from alpha if you  insert a piece of paper between
the radiation source and the counter. (paper stops beta, counter is 
a scintillation detector with a mylar window)


> 
> Also, do any of these detectors count neutrons (which are very bad)? Is a
> geiger tube detector better than solid-state (or vise versa) and under which
> conditions/uses is either "better" than the other?

Neutrons are very hard to count. Typically they are "fast" and can't be
counted until they are slowed. Polyethylene is used to slow (thermalize)
fast neutrons and then typically a boron-triflouride detector is used.

My training was with G-M detectors so I don't know about "solid state" types.

> 
> How is a roentgen (one measure of radiation) related to a REM (which I
> believe stands for Radiation Effective to Man)? What dose of roentgens/REMs
> in bad/worse/fatal? (I have been told that more than 350 roentgens is
> bad/fatal)

350 REM in a single exposure ought to be fatal. 100 induces radiation sickness
for most people. Of course these are statistical conclusions. Your 
exposure may vary! (Makes you wonder what happened to the statistical people)

> 
> 
> All follow-ups have been directed to sci.electronics.
> 
> 
> Neal

I used to know a lot more when I was a practicing Nuke. Of course my
knowlege was simply about the conditions and equipment in the powerplant.
Given a nuclear attack, I'd be only slightly more knowlegeable than 
anyone else about what radiological problems exist.

Ron Miller