Newsgroups: sci.electronics
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Radiation Detectors/Counters
Message-ID: <1989Apr26.180248.4907@utzoo.uucp>
Organization: U of Toronto Zoology
References: <5499@lynx.UUCP>
Date: Wed, 26 Apr 89 18:02:48 GMT

In article <5499@lynx.UUCP> neal@lynx.UUCP (Neal Woodall) writes:
>How exactly is a "roentgen" defined? Is it in terms of energy dose, or just
>in terms of "counts"...
>How is a roentgen (one measure of radiation) related to a REM (which I
>believe stands for Radiation Effective to Man)?

There are actually three units involved.  The roentgen is simply a unit
of radiation energy, as I recall.  The rad is, I think, "roentgen absorbed
dose", which is more related to how much of that energy gets absorbed.
And the REM is "roentgen equivalent [for] man", which corrects absorbed
energy for the biological effectiveness of different types of radiation.
REMs are what you really want to know about for health purposes, but the
instruments usually measure roentgens or rads and you have to know
the type of radiation to get REMs.

> What dose of roentgens/REMs
>in bad/worse/fatal? (I have been told that more than 350 roentgens is
>bad/fatal)

Background levels are very small, normally measured in milliREMs.  Hundreds
of REMs are very bad news.  Humans vary, so the most you can get is a
statistical measure, the LD50 -- how big a dose will be lethal to 50% of
a population.  That's something like 250-300 REMs, as I recall.  Some
sources give a tentative rule of thumb that it is reasonable to accept
a once-in-a-lifetime dose of 100 REMs in an emergency with human life
at stake.  That is unlikely to kill you but likely to make you sick (later).

All this is based on rather fuzzy memory; corrections welcome.
-- 
Mars in 1980s:  USSR, 2 tries, |     Henry Spencer at U of Toronto Zoology
2 failures; USA, 0 tries.      | uunet!attcan!utzoo!henry henry@zoo.toronto.edu