| T O P I C R E V I E W |
| Quicksand101 |
Posted - 03/18/2021 : 22:47:03
I heard of Geiger counters that have calibration that drifts over time. Why does this happen and does it happen on the GMC 500 or 500+? Is this a big concern and how do I fix it? |
| 5 L A T E S T R E P L I E S (Newest First) |
| Damien68 |
Posted - 03/31/2021 : 00:39:05
quote:
Originally posted by violet_sin
Thanks ullix,
With more study I realized the highest reading I've obtained, 25.5k cpm, was still just under half of the tubes rating. Probably not going to do anything more than it was normally intended to do, in the middle of it's usage range... so much reading to do. Love your geigerlog program BTW, huge readme I'm wading through.
in the readme there are a lot of mathematical and physical concepts to assimilate, that's why at the beginning you have to read it several times and possibly find additional information with google. but it's worth it if you want to interpret the data provided by the counter.
In addition in GeigerLog there are tools to build statistical data that all physicists use and which are necessary before making reliable interpretations because the measurements are taken from random events and without these tools you will not be helped to tell the difference between the real part, and the fantastic part of your measurements. |
| violet_sin |
Posted - 03/30/2021 : 10:31:52
Thanks ullix,
With more study I realized the highest reading I've obtained, 25.5k cpm, was still just under half of the tubes rating. Probably not going to do anything more than it was normally intended to do, in the middle of it's usage range... so much reading to do. Love your geigerlog program BTW, huge readme I'm wading through. |
| ullix |
Posted - 03/24/2021 : 00:47:01
The Life expectancy is given as >1×10E9 pulses. You'll find it in this document https://sourceforge.net/projects/geigerlog/files/Supporting%20Documents/M4011%20Geiger%20Tube%20Specification%20%28unknown%20sources%29.pdf/download
Though be warned I have no idea where these claims come from; it may or may not be valid!
But let's assume it is a billion pulses. Then at background CPM=20 it would last for 95 years. At permanent CPM=10000 it would last >2 months.
There is no reason the expect that a tube has a memory for its count history beyond the deadtime of some 100 microseconds.
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| violet_sin |
Posted - 03/23/2021 : 23:28:09
Can a tube be "aged" in an untimely fashion or deafened (desensitized) from a number of heavy readings? I understand they have a limited number of clicks the be sure. But can we induce a wandering or temporary insensitivity afterwards?
I gave my 320+ a right beating the other day with some ANGRY pebbles at >10k CPM. Mineral sample blew the doors off compared to it's natural region of sensing. Mostly background readings as I take it everywhere, to a few hundred CPM on available samples.
The background counts seemed normal afterwards, but I was concerned about it too. Didn't want to deafen the thing about the time it would be nice to "hear" my hands were clean.
I wore gloves the whole time. took some long time counts on the packaging materials and waste from shipping box after the visual inspection of my purchase. Nothing appears to be hot, except the sample, as it should be.
Probably safe to say, you could check it against any metric available to you. Similar readings over a range are about the best to hope for from a non calibrated gadget and source. Will a heavy reading ding the more fancy unit for a loop? I don't know. The 320+ faithfully chirps away though.
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| ullix |
Posted - 03/20/2021 : 00:41:38
I expect that all Geiger counters have a drift in their "calibration".
One might summarize this as "aging" - whatever this means. It could be the tube itself or the electronics. Candidates are aging of capacitors, corrosion of anything which changes resistance, contact corrosion, which all may result in certain changes impacting the efficiency of the tube or the counting circuitry. Most likely the anode voltage will drift, but pulse shaping, count discriminator level is also possible, and perhaps more.
So, if you need calibrated devices, you'll have to re-calibrate every X years, X = 1 ... 3.
ISO-certified industries must do such a certification in regular intervals. See e.g. this page for a Gamma-Scout counter certification (~$100) https://www.gamma-scout.com/en/kalibrierung/ It must be done in a qualified lab, which also needs to be certified for the purpose!
Such a calibration is not available for GMC counters. But what would be the point? These devices have never been calibrated. The existing "calibration" is basically taken "out of the blue" as a kinda, sorta, perhaps in the right ballpark, calibration.
You can do a calibration relative to any starting point, like when just purchased, and 1, 2, 3 years later. The only thing truly available for hobbyists is the use of potassium. See my "Potty Training" for more https://sourceforge.net/projects/geigerlog/files/Articles/
Keep in mind that a true calibration is valid ONLY for pure gamma radiation!
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