Fw: Fw: Re: [Milsurplus] Milsurplus Radiation

[windy10605 at juno.com]

Here is where I'm at with the Milsurplus radiation subject I mentioned
earlier. I tend to really dive into things. Comments and further input
are welcome.

73 Kees K5BCQ

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Ionizing Radiation Readings Summary
(or, what I found out after setting off the "Hot Load" detector at the
salvage yard with some old surplus Military equipment in the back)

Ionization Radiation has been "interesting", but mostly a mystery to me,
since I'm part of the "duck and cover" generation, so I decided to browse
the Internet and see what I could come up with to put it into simple
perspective, since over-reaction seems so prevalent today. 
There are four types of Ionizing Nuclear Radiation of interest:
Alpha particles (stopped by a few inches of air or human skin)
Beta particles (stopped by thin wood, metal, or plastic)
Gamma rays .....similar to X-rays (stopped -only- by a substantial
thickness of lead, concrete, etc)
Neutrons released by Nuclear Fission
Instrumentation, mostly old Civil Defense radiation survey meters which
are readily available today, only measure Gamma or Gamma and Beta, so my
focus was on those two. 
Radiation effects on humans is based on an accumulated dosage over time
(amount integrated over time). Radiation is all around us and the average
yearly dose for citizens of the USA from ambient/background radiation is
around 360 mR/Year (or 3.6 mSv/Yr, Sievert is the new unit of measure, 1
Sievert = 100 Rems). I'll use both, since most of the available
instrumentation indicates in "Rems". This background radiation comes from
various sources: cosmic, radon, terrestrial, internal, consumer products,
diagnostic X-rays, fossils, nuclear medicine, etc. In addition to this
background radiation, limits have been set for additional average
radiation rates of : 100 mR/Yr (1 mSv/Yr) for the unmonitored general
public, 150 mR/Yr (1.5 mSv/Yr) for airplane crews due to the high
altitudes and less "buffer" to cosmic radiation, and 2000 mR/Yr (20
mSv/Yr) for monitored nuclear industry workers. A yearly USA public
ambient/background radiation level of 3.6 mSv/Yr would work out to 306
mSv for an 85 year lifetime. 350 mSv per lifetime was the criterion for
relocating people after the Chernobyl accident. Unfortunately, many
people received WAY in excess of that. That basically covers the range
.....please note that the units are in milli-Rems and milli-Sieverts,
1/1000 of a Rem and Sievert. 
Most of the Civil Defense radiation survey instruments I've seen are
basically of two types. Gamma ray survey meters of the CD V-715, CD V-717
type with meter scales showing a rate of 0-0.5 R/Hr, 0-5 R/Hr, 0-50 R/Hr,
and 0-500 R/Hr. The --lowest-- usable reading off these instruments is a
radiation rate 0.1 R/Hr = 100mR/Hr (translates into 876,000 mR/Yr),
--way-- too high for day to day measurements. These are good to show you
"hot" areas after a nuclear blast, but if you get any substantial reading
on one, it's out of adjustment (high probability) or you are in BIG
trouble. The other type of instrument (CD V-700 type) measures both Gamma
rays and Beta particles and uses a Geiger tube. The meter scales show a
rate of 0-0.5 mR/Hr, 0-5 mR/Hr, and 0-50 mR/Hr .....even less on some
instruments. These will measure background radiation and are ideal for
checking out surplus equipment for radiation levels.
I've looked at three manufacturers of these CD V-700 type instruments
(Victoreen, Lionel, and Electro Neutronics) for a couple of weeks and I'm
most impressed by the CD V-700 made by Lionel Corp. The reason is that
their circuit is simple and straight forward, they use high quality film
resistors, only two "D" cell batteries, and they have a more robust
Geiger tube probe assy. 
The other scale on the meter is in Counts/Minute (C/M) which is a far
more accurate way of making measurements. There is no relationship
between C/M and mR/Hr except on --that-- particular instrument. Counts,
or "clicks" per minute depend on the sesitivity of the Geiger tube and
the particular circuit design. Some may have 300 C/M = 0.5 mR/Hr with a
linear relationship and some may have 800 C/M = 0.2 mR/Hr with a linear
relationship. Since the meter works off a "click" integrator/averaging
R/C network, the click count for one minute will be a better indication
of small changes in radiation levels than the meter. That's why adding a
simple frequency counter is a good idea if you are prospecting rocks of
making measurements around the house/yard/storage shed. I think you can
adapt one of the many frequency counter circuits available, like the
NorCal FCC-1 by changing the code slightly (I'm looking into it).
I did some quick experimenting and found that substituting a 1B85 Geiger
tube assy (the individual tubes can't be swapped due to size/connection
differences) for the 6993 Geiger tube assy in my Lionel CD V-700
--greatly-- improved the low end and background sensitivity. What a
difference, but my 6993 tube may be weak ? They all appear to run on
about 850VDC so a swap should be OK. Add a BNC connector to make probe
swapping easy. 
The CD V-700 literature says ambient/background radiation should read
0.01 to 0.02 mR/Hr (0.1 to 0.2 uSv/Hr ....that's micro-Sieverts) or about
20 C/M ("clicks" per minute) since you can't read the CD V-700 meter at
those levels. 
The EPA/NCRP "acceptable" maximum levels for the unmonitored general
public, as I see their data, would be 360 mR/Yr (3.6 mSv/Yr) plus
100mR/Yr (1 mSv/Yr) = ~ 500 mR/Yr (5 mSv/Yr). I'm not using the monitored
nuclear worker "acceptable" levels but, just as a sanity check, they are
4x higher. 500mR/Yr (5 mSv/Yr) would translate into an average hourly
rate over the whole year of 0.05 mR/Hr (0.5 uSv/Hr ....thats
micro-Sievert). A much higher rate can be received over a short period of
time which would still average out OK over the year. The typical CD V-700
has a safe Beta radiation test/calibration source on the side which
outputs ~2 mR/Hr (0.02 mSv/Hr) on average. 
A little common sense here. That 2 mR/Hr (0.02 mSv/Hr) level is safe for
the intended use, but I would leave it in place, don't 'scrape" it off,
don't make it into something to wear, and don't ingest it. Same goes for
radium dials, watches, compass, altimeters, or meter faces. Use them "as
is" and leave them alone. They are perfectly safe behind glass, try not
to take it apart ....if you do, wash your hands well, please don't scrape
the material off, and don't ingest (breathe or eat) the radium material
if you do scrape it off.


Now for some actual Beta/Gamma measurements (at the item, decreases with
distance):

Measuring and calibrating to the test sample on the CD V-700 ..........
1.6 mR/Hr
Ambient levels .......................................................
<0.05 mR/Hr 
(can't read meter, measured 14 C/M which sounds reasonable relative to
spec)
Old compass ...........................little over ambient, can't tell
with meter
Various radium dial meters ............little over ambient, can't tell
with meter
Military Westinghouse (radium) 0-150V meter.............................
4 mR/Hr
Dial (radium) on Military RBZ...........................................
3 mR/Hr 
Military OS-24 Synchroscope (it's the tuning dial, not the CRT)........
14 mR/Hr