🚀 go-pugleaf

> /* Written  5:49 pm  Apr 25, 1989 by neal@lynx.uucp in uxe.cso.uiuc.edu:sci.physics */
> /* ---------- "Radiation Detectors/Counters" ---------- */
> 
> 
> I have recently decided to purchase a geiger counter, for general use and for
> possible survival applications. I have seen several different types of devices
> offered for sale, including some that are old US Civil Defense surplus, some
> that are based on solid-state sensors that are obviously commercial-grade
> units, and some that are advertised as being European/NATO surplus (brand new,
> never opened).
> 
> Now for questions/confusion:
> 
> I believe that the geiger counters that I have seen can be broadly classed
> "radiological health" units (measure in the .5 to 500 milli-roentegen/hour
> range and are not "hardened" or weather-proof) and those that are intended
> for military/war conditions (measure in the 1-500 roentgen/hour range and are
> "hardened" and weather/water proof).

   This is basically correct.  The high range instruments will not be useful
to you unless you happen to be near a nuclear explosion :-)

> 
> 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?

  The Roentgen is defined as the amount of x or gamma radiation which will
produce 1 E.S.U. of ionization in a cc of air at STP.  The Roentgen is NOT
DEFINED FOR beta, neutron or alpha radiation.  Normal background radiation
depends on where you live.  An average for the U.S. is about 50 milliroentgens
per year, but that's only from external gamma and x-rays.  
> 
> 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?
> 
   G-M detectors are insensitive to neutrons.  G-M are best for detecting 
> beta radiation.  Solid detectors such as NaI are best for x and gamma rays.
> 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)
> 
  One roentgen (1 R) of x or gamma radiation deposits about 87 ergs per gram
of air.  The same exposure will deposit about 93 ergs per gram of soft tissue.

The roentgen is a unit of EXPOSURE.  In order to relate x or gamma exposure 
to ABSORBED DOSE, we use the rad unit (Radiation Absorbed Dose).  ANY type
of ionizing radiation dose can be characterized by the amount of energy 
deposited per unit mass of material (ANY material).  One RAD is equal to 
an absorbed dose of 100 ergs per gram.

Since some type of radiation are more effective than gamma rays in producing
biological effects, we need a way to "normalize" the absorbed dose units.
We do this by converting the absorbed dose in RADS into a "dose equivalent"
in REMS.  In general, it is assumed that 1 RAD of x or gamma ray dose yields
1 REM of dose equivalent.  On the other hand 1 RAD of thermal neutron dose
yields 3 REM of dose ezuivalent.  1 RAD of fast neutron dose yields 10 REM
dose equivalent.  One RAD of alpha dose yields 20 REM of dose equivalent.
One RAD of beta dose yields 1 REM of dose equivalent.

The conversion factor used for converting from RADS to REMS is called the
Quality Factor (QF).  The QF is defined in terms of the linear energy transfer
of the type of radiation in question (amount of energy transfered to the 
medium per unit path length).

Regardless of the type of radiation in question or the means of exposure, a 
REM produces the same amount of risk.  (Actually there may be other 
"modifying factors" which might be applied in the conversion of absorbed 
dose to dose equivalent in certain situations, but it would be beyond the scope
of this note to discuss them here.)

Great care should be excercised when using geiger counters for determination
of dose or dose equivalent.  G-M's are, by nature, only flux-measuring devices-
they do not measure energy deposition.  G-M's should only be used for 
qualitative assessments such as contamination surveys unless specifically
calibrated (or "energy-compensated") for specific situations.

The LD-50 dose (lethal within 30 days in 50% of those exposed) is about
400 rads (can vary greatly depending on the individual and medical attention).
The average annual NATURAL background dose equivalent is on the order of 
300 millirem per year (this includes RADON).