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[aprssig] An accurate do-it-yourself radiation meter

WD8ARZ wd8arz at ix.netcom.com
Sat Feb 11 12:22:37 UTC 2012


Hello Bob, and interesting you latched on to this type of detector.

The article you provided a url to, refers to the difficulty of getting GM 
tubes and there expense. At the time of his article that may have been a 
factor, there is price gouging and your not going down to Radio Shack to get 
a gas GM tube. But they are readily available on the internet and are much 
cheaper when purchased from the suppliers and not the middle men jacking up 
the price .... especially cheaper in quantity. A friend of mine bought 100 
in a lot and we have been building home brew units the last few months. We 
are about to update the units we had built with a single GM tube to a dual 
tube. More sensitive and surprisingly a good performer compared to more 
expensive units. I have a professional Inspector Alert that I have made 
comparisons too, along with safe low lever steady radiation sources to test 
with. - Designed and built by WA8YKN, Ashland OH - Using SBM20 GM Tube

http://www.hotray-info.de/

In addition to the two Geiger systems I have on line reporting as I shared 
in a previous email, I bit the bullet and bought a program that works on my 
Epic phone for detecting radiation. This was in preparation to setup a 
system to report via APRS, especially while mobile.

There are definitely plusses and minuses to the Epic system, and the minuses 
are severe enough to not make this a first responder tool. Hi Hi  In the 
cell phone area, the sensors were not intended for use as a Geiger counter, 
so the performance is all over the map from phone to phone and temp of the 
phone affects the noise level considerable..... thus a new base line that 
has to be calibrated against to get proper counts per minute reliability 
(CPM).

The plus side for solid state:
Each pixel element in the mosfet camera pick up is a Geiger Mueller tube. 
That means multiple hit / counts are possible at the same time, and is 
capable of a fast series of counts due to no dead band after a trigger 
event. Due to the dead time from triggering a count in a gas gm tube to the 
time it takes for the tube to recover, radiation event counts are missed. A 
solid state Geiger tube is more physically reliable and not as easy to 
damage from moisture as a gas gm tube. Due to its lower sensitivity, I was 
able to use the Epic and to locate the component in several circuit breakers 
that had a radioactive component to them, and they didn't glow in the dark.

The negative side for solid state:
Temp sensitivity generates a noise base line reducing and varying the 
sensitivity, varying sensitivity across the detecting surface, mounted 
behind lenses that block out Alpha and Beta radiation emissions, can over 
saturate a solid state sensor with exposure to radiation particles that will 
permanently affect the performance of the device .... similar to over 
exposing a solid state gas sensor with gas vapor (aka as in smoke alarms). 
Various solid state sensors will sense some types of radiation sources and 
not others, or have a large varying sensitivity to the range .... gm tubes / 
construction types are influenced by this too.

My experience with the software installed in my Epic is not useful to 
protect me as it is not sensitive enough, and has difficulty from sorting 
radiation detected events from internal noise generated in / or to the 
device events. However, for close in measurements over time of suspicious 
resources, it does work.

There is much more I could share, but don't want to stray from the thread 
too far .... hi

Radiation Map Sites Of Interest:

http://www.radiationnetwork.com/  Great for US of A, has more contributors 
than other map site.

http://www.blackcatsystems.com/RadMap/map.html  Great for Japan, has more 
contributors than other map site.

The home brew units mentioned above are reporting from the Denver, South 
Bend, North Central Ohio, and East of Nashville Tn areas.

73 from Bill - WD8ARZ
EMCOMM HFN MarsAle Pilot Station
http://hflink.net/

----- Original Message ----- 
From: "Bob Bruninga" <bruninga at usna.edu>
To: "'Phil'" <philmt59 at aol.com>; "'Tacos AMRAD'" <tacos at amrad.org>
Cc: <aprssig at tapr.org>
Sent: Friday, February 10, 2012 6:29 PM
Subject: Re: [aprssig] An accurate do-it-yourself radiation meter
>

> What I don't get is the 2 orders of magnitude difference in capture area.
> Sure, ANY PN device can in someway be a radiation detector, but the Geiger
> tube has a hundred times more capture volume than most any PN device.
>
> So as far as giving an idea of background radiation, I cannot see these
> point source detectors as much more than a curiosity.  Or I am missing
> something.  I think the best detector is a LCD display with background
> plazma lighting.  Bias the lighting electrodes just below threshold and 
> then
> any event anywhere in the 1/2 square foot area should be detectible?
>
> Subject: Re: An accurate do-it-yourself radiation meter
>
> http://www.elektor.com/news/elektor-hardware-tip-improved-radiation-meter.20
> 78018.lynkx?utm_source=UK&utm_medium=email&utm_campaign=news
>
> Or am I missing something.
>
> Bob, WB4APR




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