| Author |
 Topic  |
|
|
jboy55
USA
1 Posts |
 Posted - 12/31/2022 : 11:04:02
|
Hi All,
I have always been interested in radiation, and this year Santa (my wife) got me a GMC-320s off of Amazon. Upon turning on, it read 23 CPM, and I tried unsuccessfully to find anything around the home that would read higher. I bought an Images SI Inc, Uranium sample off Amazon and it just came today. The cert says it should read 1044 CPM, but I cannot get my counter to read anything above background.
Am I doing something wrong? It would surprise me that the sample would be so far off, did I get taken by a known scam selling rocks as Uranium? Or is the counter defective? |
|
| Reply #1
ullix
Germany
1171 Posts |
Posted - 01/01/2023 : 02:06:46
|
23 CPM sounds reasonable, but no increase with a Uranium sample does not. Can you post this "certificate"? I don't see how they could make a statement that it should read "1044CPM". Sounds more like a fake.
I suggest to take a look into my "Potty training" article https://sourceforge.net/projects/geigerlog/files/Articles/
It deals with the use of household articles which contain enough Potassium to give good readings with a Geiger counter. You may find elevated levels of Potassium also in floor tiles, wall tiles, and -easy to get - Cocoa powder from the supermarket.
If this stuff doesn't get you to counts in the CPM=100...200 range, then the counter may be defective.
|
 |
|
| Reply #2
EmfDev
2250 Posts |
Posted - 01/03/2023 : 12:52:49
|
Hi jboy55, the sensor is located towards the back (bottom) try to place the sample as close to there as possible. And also 1044 CPM from what sensor/tube/geiger counter?
If you have a smoke detector, you can also test that. With the correct angle/position as close as possible to the smoke detector, you can get a higher reading than background. |
|
|
| Reply #3
violet_sin
USA
20 Posts |
Posted - 01/04/2023 : 08:59:37
|
In the picture provided on Amazon when that product is searched, it shows what looks to be a wand probe with a LND 712 end window alpha sensitive tube. My best guess. And the rocks look to be set right up against it. With only ~1KCPM on an alpha sensitive tube, that close, it may not hit too hard on the GMC-320, especially if not lined up with the GM tube on your machine. They only claim the samples active, not hot throughout, and finding the side/facet with an active area may take a moment fiddling with it near the case vents over the tube. Best is beside the vents as to not drop active debris in there, or setting the correct portion of your 320 over the sample.
I outlined my GM tube with sharpie on the back for rapid identification of test zone and easy centering. That may be helpful to you.
Learning that rocks sold after being graded with a Ludlum 44-9 probe, do not live up to the those specs on a GMC-320+, was not fun when first collecting. it simply doesn't see most of the activity. Things rated a few KCPM can end up reading maybe a few hundred CPM. The comparison between a GMC-320 and a LND 712 should be less drastic, as it's got a much smaller active area than the Ludlum 44-9 pancake. But I don't know how much, as I've never used one or made a comparison chart.
Line that sample up to the tube and roll it showing all sides around to see if it goes above background count, it should, but I don't imagine it will be too impressive.
Hope any of that helps
Aaron- |
|
|
| Reply #4
ullix
Germany
1171 Posts |
Posted - 01/05/2023 : 04:33:54
|
@violet_sin: why don't you post a link to the Amazon offer?
The Ludlum 44-9 pancake https://ludlums.com/products/all-products/product/model-44-9 is rated at
quote:
Typical Sensitivity
(137Cs gamma) 3300 cpm per mR/hr
Note that it says Gamma, NOT beta, NOT alpha!
which equates (see chapter "Deprecated Radiation Units" in GeigerLog manual) to: quote:
330 CPM / (uSv/h)
This is on a par with the LND7317 pancake tube, rated marginally higher at 348 for the same Cs-137 source, used in the GMC-600 counter. For reference: the tube M4011 is assumed to be 154 (a published calibration does not exist).
A Uranium sample will have a significant amount of decay products, and most will also emit beta, some strongly.
If the sample is Uranium, you will see it in all counters 300, 320, 500, 600, ...
|
|
|
| Reply #5
violet_sin
USA
20 Posts |
Posted - 01/05/2023 : 10:10:30
|
Sure, simply search "si inc, uranium"
https://www.amazon.com/Images-SI-Uranium-Ore/dp/B000796XXM
There are 3 pictures, of the last of which shows the probe and a rock shoved right up against it.
LND makes the sensor for the 44-9 also looks to be a LND7311, from timestamp 1:06 https://m.youtube.com/watch?v=z1rxUxwQKu8 in that vid the presentor states it's for alpha/beta/gama at time stamp 0:15 )
Weak uranium samples can easily show little to no activity from the wrong side of the rock if it's a thin secondary entrustment over a crack that was only on one facet of the rock with the rest being a matrix of boring blocking material. A few centimeters of rock blocks a lot, a couple inches more so, if there's not a lot of emissions, well they don't shine through. That's my experience with the 320+ I have an a pile of rocks purchased and measured from a nice vendor on bonanza site by the name of Rockhound_Steve, mostly todilto limestone. He used to sell 6# lots with some high, some low and a bunch of mid active rocks. His shop looks empty right now, but I purchased from him like last November, so IDK why.
Not trying to be argumentative or anything. He measures with a Ludlum 44-9 and a Ludlum 2200 ratemeter/scaler, marks the active area with correction fluid (white-out). Rocks with grains of actual uraninite would show activities roundabout. I got one showing 123K CPM on one side and the other was FAR lower, have to dig out my notes to see, but it was just a rich entrustment of secondary. Alphas flying all over the place, dead dead rock matrix was a good shield for the rest on the back.
So that's not your spec sheet data there, but I've a pile of rocks and several meters, a note book and vids of my research as an amateur hobbyist finding out what they see. It's more experience than science, but I try.
Saying any uranium sample will have a significant amount of beta activity, remember there's not always much uranium there at all. It can be yellow, but there's plenty of vanadium in there too. Get a real hot sample with actual amounts of U there, SURE, you've something to measure... Those limestone chunks, were not strong carriers often times, if you check with a scintillation probe. Radiacode 101. Lucky to see into the 20uSv/h range. Pitchblende samples 90uSv/h with radiacode/ 120uSv/h GQ GMC320+v4
But I don't think you can own such samples Ullix, if I recall correctly in your country is illegal. Looking forward to your response |
Edited by - violet_sin on 01/05/2023 10:18:22 |
|
|
| Reply #6
ullix
Germany
1171 Posts |
Posted - 01/06/2023 : 03:07:36
|
@violet_sin: You are over-estimating the liberty in Germany for obtaining certain compounds: when I search in Amazon.de for "Uranium", all I get are book offers, with enticing titles such as "Marijuana Today ... Uranium Tomorrow" ;-)
https://www.amazon.de/Marijuana-Today-Vanadium-Uranium-Tomorrow-ebook/dp/B07LDGKQGJ/
Thanks for the helpful links.
The uranium ore is measured with the GCA-07 Geiger counter (https://www.imagesco.com/geiger/digital-geiger-counter.html) , which uses a LND 712 tube, the very same one as in the GammaScout counters. It has a small Mica window, so is sensitive also to alpha. It sensitivity had been given by LND (this info is now removed from their web site) as 108 CPM/(uSv/h) but for Co-60! In my estimate its Cs-137 sensitivity would be approx 125.
LND is now offering a LND 7121 tube, which is identical to the 712 in all mechanical and electrical aspects, except that it uses a stainless steel window (for more stability???)! This tube now is qualified with a sensitivity of the exact same 108, but now for a Cs-137 source (what a strange coincidence ...).
As the video showed, the Ludlum 44-9 uses the LND 7311 tube, which has exact same dimensions as the LND 7317, both use a Mica window, but they differ in electrical specs, and in Cs-137 sensitivity:
in units of: CPM / (uSv/h):
LND 712: 108 (Co-60)
LND 7121: 108 (Cs-137) (hmmm?)
LND 7317: 348 (Cs-137)
LND 7311: 330 (Cs-137)
M4011: 154 (assumed, no calibration data available)
I recommend watching the video, in particular when longing for an energy compensated Geiger tube. It nicely shows (@6:20) that this is achieved by reducing the overall sensitivity to its lowest value over the region of choice!
The Ludlum page (https://ludlums.com/products/all-products/product/model-44-9#graphs) is actually giving you more details on the tube than LND itself. First you see the energy response curve for gammas, and then for betas, shown here:
Remind you that the gamma sensitivity is in the sub-1% range! All Geiger tubes are much, much more responsive to beta!
With respect to the Amazon pics, the ore sample had been tested in almost direct contact with the Mica window. And the very fact that the count rate is strongly dependent on the orientation of the sample to the detector supports the notion that it is mostly beta, what the counter sees, because gamma would be only mildly absorbed by the small piece of ore!
Of course, the percentage of radiation of uranium as beta is high, but if there is no Uranium in the sample, then there is neither gamma nor beta!
For measuring with a GMC-320 counter you may have to remove its back plate, so that you can get direct contact between tube and ore. I cannot imagine that you can get 1000 counts with a LND712 tube, but none with a M4011 tube. If you get none, then either the sample is a dud, or the counter is defect!
One more thing to consider: once you get a significant percentage of counts from beta, then all Sievert units (uSv/h) are completely and utterly meaningless! The Sieverts are calibrated for gamma, and gamma only. I am not even sure how to calibrate for betas. Don't report "uSv/h" when you measure beta; CPM is all you can do!
|
|
|
| |
Topic |
|
|
|
New GMC 320s - Images SI sample not reading
