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GMC-300/GMC-320 - An Affordable Gieger Counter
#1
For those interested in an affordable GC, the GMC-300/320 are great options from GQ electronics. These units have a LCD display and are capable of recording measurement data for later analysis on a computer.

I personally have the GMC-300Eplus and the GMC-320Plus. Both are good for the price. I've dropped both units a couple of times and haven't broken either. There are a couple of issues i've had with these units, but overall, they are still ticking away.

The issues I've noticed are both temperature related. I believe it may be circuitry related, but possibly also GM tube. The GMC-300Eplus loses its ability to sense (or create pulses from the GM tube) in very high temperatures (90+F). When I drove to California last year, if left in the hot car while I was grabbing some food, I would find it reading 0CPM/mR/uSv. Once I cooled it down with AC it would start registering counts again.
For the GMC-320, it had the opposite problem where in cold ambient temperatures (below 40F) it would start counting more. Additionally, when pointing the tube window of the GMC-320 at the sun, readings would spike. Interestingly some of these behaviors have changed over time. The 320 is no longer as sensitive to cold or direct sun now.
All in all, they behave very well indoors and in pocket. I can't say I would recommend them for outdoor monitoring based on my observations.

Another thing is the GMC-300 came with a NiMh 9v rechargeable battery where as the 320 has a 3.7v LiON battery. In my opinion, I liked the 9v option better, as you could just put in a regular 9v battery if needed. I believe GQ has changed the 300 to a LiON battery now also, but I'm not 100% sure on that. 

Both units have a USB port for charging and data. There is also a pulse output to connect to different types of measurement equipment. either unit can be used with a number of monitoring websites to provide real-time global monitoring. There is also some software provided from GQ electronics to use the GC connected to a computer.

I've had the 300 since 2013  and I purchased the 320 in 2014. Both batteries are starting to go, but I do keep them both on all the time and usually plugged in to charge. I paid less than $130 per unit. Better deals can be found on eBay than the prices on their website. Looks like prices have already come down...

http://www.gqelectronicsllc.com/comersus...ategory=50
 
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#2
Hi Roger, thanks for the review. I've been looking for something affordable. not sure yet what I need though. Would like something that could detect plumes in the air from Fuku or WIPP or Hanford or the next accident. Also curious how various consumer products would test. Heard stories that higher detections can be found on the road following diesel trucks, but is it true? A lot of uranium mining and superfund sites in my area I'd like to compare to each other and to my already high background. Probably out of reach but it would be fun to put together a station equivalent to the Radnet station that is sometimes online, so people could compare and contrast readings.
"The map is not the territory that it is a map of ... the word is not the thing being referred to."
 
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#3
Marco Kaltofen goes ngenie... https://twitter.com/MKaltofen (tried to attach screen shot, less than 500kb, crashed Torch each time)...
Pia
Jitsi chat: enfo.pia@gmail.com
 
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#4
(03-18-2016, 06:48 AM)Horse Wrote: Hi Roger, thanks for the review.  I've been looking for something affordable.  not sure yet what I need though.  Would like something that could detect plumes in the air from Fuku or WIPP or Hanford or the next accident. 
From the options I've looked at, it is the best bang for the buck. I find it more educational to start with something cheap and simple and then work my way up. That way I don't over-invest.

There have been many days where the alarm on my unit goes off for a few seconds, sometime up to a couple of minutes. I personally set my alarm limit at .028mR/h which is a significant measurement. Here in Denver, the background min/max is .01-.025 mR/h (.1 - .25 uSv/h). Don't forget that there are other plumes that are not man-made. For example, Radon from nautral sources can set off a gieger counter too. Of course, niether are any better for humans than the other. While I can't verrify if the high readings I caught were actual plumes from man made sources, it was valuable to know something was there.

Plume detection would be dependent on many factors. Having the unit exposed to outdoor air, vs. keeping it inside, would have an effect on the readings and ability to detect something like a plume. Another thing to consider is the type of radiation from a plausible plume. The type of decay would change how detectable a plume is in general. If the primary decay of radioisotopes in a plume is alpha, you would need different type of detector (this unit won't pickup alpha). Beta decay is detectable, but having the detector inside would block all beta from outside except any carried inside via the air vector. If a plume was primarily gamma decay or x-ray, then detection would be possible from even inside a structure.

(03-18-2016, 06:48 AM)Horse Wrote: Also curious how various consumer products would test.  Heard stories that higher detections can be found on the road following diesel trucks, but is it true?
I've driven around with my GMC 300 and 320 and have never noticed a significant increase when following a diesel truck. However, I can't say I was trying to prove that, it was just general monitoring. That doesn't mean there isn't measurable radioisotopes in the combustion byproduct of diesel fuel though. You might be able to detect that with a more sensitive instrument or in a more controlled setting. Again, the GMCs are not super sensitive, they are meant to be general detection instrument. A good analogy is these are like a 25' tape measure. You can't measure everything, but you can measure a lot of things.

(03-18-2016, 06:48 AM)Horse Wrote: A lot of uranium mining and superfund sites in my area I'd like to compare to each other and to my already high background.  Probably out of reach but it would be fun to put together a station equivalent to the Radnet station that is sometimes online, so people could compare and contrast readings.
You should be able to pickup exposed uranium tailings with this unit. i can't confirm yet, but I would expect that to be true.
From what I know, the Radnet monitors are setup with a blower (fan) and a filter. The counter/tube is located above the filter so a very high volume of outdoor air is passed in front of the sensor and particulates that can be captured on the filter will be concentrated. I believe the filter is to calculate/watch decay of isotopes, permitting possible remote determination of what the filter captured. ..but I'm not an expert...
 
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