| T O P I C R E V I E W |
| Tony81269 |
Posted - 09/20/2024 : 17:40:06
Some of you know that I have had a new GMC-800 calibrated to NIST/NRC standards at Applied Health Physics. If you'd like to see more information about that please see topic "NRC Calibration". My intentions now are to check the accuracy of this meter. I have access to small check sources and some CS-137 at approximately 220 mCi. Before calibration I had compared the GMC-800 to a Ludlum 3 meter. The comparison between the uncalibrated GQ meter and the calibrated Ludlum were surprisingly close. I have decided for now not to compare the two meters. They are vastly different and the Ludlum 3 actually has poor accuracy. I am going to attempt to do different tests based on what the math says it should be and what I actually get. I may use the Ludlum on occasion just to see if they are close. If you have any ideas you'd like to see then let me know. Although I will not screw around with any of my cal, dt, or voltage settings.
First test was an easy one. I'm not at work right now so all I have with me is 4.525 uCi check source. The source was born 5/1/2014 and so decay puts the activity now at 3.561 uCi. I placed the check source 2" away from where I think the tube is inside the meter. So at 2" away, a 3.561 uCi source should read 0.445 mR/h. The resulting measurement I got was 0.46 mR/h. I tried this several times and every one was close to that value.
I can't really do anymore good tests until next week while I'm at work but if you see anything in this picture I did wrong or you have a comment, please let me know.
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| 27 L A T E S T R E P L I E S (Newest First) |
| Tony81269 |
Posted - 10/11/2024 : 17:57:36
quote:
Originally posted by GTS
Congratulations!
Thank you!
First day I get the letter from the NRC that I was officially the RSO, I got a call from an inspector for the ND DEQ. One of our guys who had been doing some coal logging was inspected and they found about four things wrong. Minor things like container labels, etc. I had to listen to this inspector talk for about an hour. They are supposed to send me a letter that I have 30 days to reply with corrective actions that were taken. So yeah, that was my first day  |
| GTS |
Posted - 10/10/2024 : 11:37:02
Congratulations! |
| Tony81269 |
Posted - 10/08/2024 : 15:41:07
Well everyone, I really wanted to test this meter out in the high ranges but I was recently promoted to RSO of the Company. Got my letter from the NRC last week. So yay for me I guess. A lot more responsibility. I'll try to get back to this as soon as I can |
| Tony81269 |
Posted - 09/23/2024 : 19:13:57
quote:
Originally posted by Stargazer 40
Mine was Large B-Cell. Came from artificial sweeteners like 99% sure. Twenty years ago. We've each had enough exposure with PET scans that lung cancer is more an issue than anything I'm messing with. My problem with at least the little sources is that they will always be farther away from your dosimeter than the fingertip or palm that the little guy is being held with or resting in. Hence likely not being recorded.
The fact is that all we really are dealing with is statistics that some government agency has made a judgement call about. Pretty sure we know what amounts are likely to kill us. But how does one assess genetic damage. All of these GM meters I can max out tube range with my little sources except for my survey meter (CDV-717) and my GQ 500+ tube two. Can barely move the needle on those. Yet for some these smaller amounts do affect things. I look at lifetime amounts as cumulative exposure risk. Again judgement call.
Anyway looking forward to your results. You have done all of us and GQ a great service by documenting the certification process and showing us your numbers. The consistency of the tubes and hardware pretty much make it a no brainer to take your calibration numbers and put them in one's GMC-800. In my opinion a better solution especially at the high end. Thanks!
And I very much enjoy the logging discussions and background. Lots of memories brought to the fore. Was lucky to have a job for forty years I couldn't wait to get to work each day.
I had to do leak tests today on 17 sources that are down in underground pits. You don't get much while those lids are closed but when you open them and pull up a basket full of sources you get the picture below. This was with the meter next to the pit. It's reading in uSv so the mR/h was about 540. Crazy huh 
I could also go back and look at the dates of calibration. It seemed interesting but I didn't really examine it much.
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| Tony81269 |
Posted - 09/23/2024 : 18:42:14
One thing I forgot to say is the meter has a "Fast Estimate". I had it set to dynamic and found that the meter was giving too much variation. I put it to 60 seconds and was then able to get good results. Maybe it's just when trying to measure this low dose rate? Because I remember before that I was getting good results at higher dose with that set at dynamic. I really don't know |
| Tony81269 |
Posted - 09/23/2024 : 06:40:43
quote:
Originally posted by Stargazer 40
Mine was Large B-Cell. Came from artificial sweeteners like 99% sure. Twenty years ago. We've each had enough exposure with PET scans that lung cancer is more an issue than anything I'm messing with. My problem with at least the little sources is that they will always be farther away from your dosimeter than the fingertip or palm that the little guy is being held with or resting in. Hence likely not being recorded.
The fact is that all we really are dealing with is statistics that some government agency has made a judgement call about. Pretty sure we know what amounts are likely to kill us. But how does one assess genetic damage. All of these GM meters I can max out tube range with my little sources except for my survey meter (CDV-717) and my GQ 500+ tube two. Can barely move the needle on those. Yet for some these smaller amounts do affect things. I look at lifetime amounts as cumulative exposure risk. Again judgement call.
Anyway looking forward to your results. You have done all of us and GQ a great service by documenting the certification process and showing us your numbers. The consistency of the tubes and hardware pretty much make it a no brainer to take your calibration numbers and put them in one's GMC-800. In my opinion a better solution especially at the high end. Thanks!
And I very much enjoy the logging discussions and background. Lots of memories brought to the fore. Was lucky to have a job for forty years I couldn't wait to get to work each day.
I totally agree about the Government. I mean they probably have done studies but in the end, it was a judgement call about things.
Also, if GQ changes components in new ones, those numbers will change so always look out for that. Sometimes, I just like testing stuff out. This company says its meter can do certain things. I want to see if it's true. From what I've seen so far is that these are accurate. More than an old ludlum 3.
I'll get back to you guys as soon as I get any results. What I'm concerned about is with a source laying on the ground like that, the gamma rays are not really focused or collimated. I'm wondering if math is going to work out correctly if you measure at a good distance. If it doesn't match up to what the math says then I'll put the Ludlum next to it and compare |
| Stargazer 40 |
Posted - 09/23/2024 : 02:50:25
Mine was Large B-Cell. Came from artificial sweeteners like 99% sure. Twenty years ago. We've each had enough exposure with PET scans that lung cancer is more an issue than anything I'm messing with. My problem with at least the little sources is that they will always be farther away from your dosimeter than the fingertip or palm that the little guy is being held with or resting in. Hence likely not being recorded.
The fact is that all we really are dealing with is statistics that some government agency has made a judgement call about. Pretty sure we know what amounts are likely to kill us. But how does one assess genetic damage. All of these GM meters I can max out tube range with my little sources except for my survey meter (CDV-717) and my GQ 500+ tube two. Can barely move the needle on those. Yet for some these smaller amounts do affect things. I look at lifetime amounts as cumulative exposure risk. Again judgement call.
Anyway looking forward to your results. You have done all of us and GQ a great service by documenting the certification process and showing us your numbers. The consistency of the tubes and hardware pretty much make it a no brainer to take your calibration numbers and put them in one's GMC-800. In my opinion a better solution especially at the high end. Thanks!
And I very much enjoy the logging discussions and background. Lots of memories brought to the fore. Was lucky to have a job for forty years I couldn't wait to get to work each day. |
| Tony81269 |
Posted - 09/22/2024 : 15:32:40
quote:
Originally posted by Stargazer 40
I second GTS comment. I freak when I see people handling even these teaching sources. I have never touched one. I have a pair of stainless steel aquarium tongs 15" long. Perfect for moving these things around and even the foot I am away from them instead of holding in my hand or with fingers just makes me feel better. $8 on Amazon. Cheap insurance.
And yes, you're messing with some potent stuff. I envy the access but I'm glad you're doing it and not me. :-)
Oh, and I store them in a lead pig about 3" tall and inside diameter of the disc. About 3/8" thick walls. I keep those in a one foot square box centered with plastic peanuts.
It's good you are careful like that. You should be even with these small sources. Nothing wrong with that at all.
I just happened to get into a job 18 years ago that required me to deal with this stuff. We do have long source handling sticks that keep it at a distance. Another thing is the source holder(bullplug) has a tungsten insert in the part that faces you while you are carrying one with a stick. The tungsten creates a window behind the source where you stand so the dose is minimal at that point. It's still way over what you would want to deal with though.
Now, what I'm going to do next week might be considered reckless. It is not in the line of work but just to test a product. Still, this product could one day be what we use. Now that I have it calibrated, I can use it legally at work. Time, Distance, Shielding. As Low as Reasonably Achievable. All things we are taught from the start.
I have not been an actual well logger all these years. My job has been to test our logging tools before they go out the door. We have some test wells that we log them in as QC. Also, I have been engineering's guy that when they want to know something they have me do it. And I'm telling you, I've done some crazy tests with large sources over the years. Stuff that would required me to be too close and for too long. But the thing right now that concerns me the most are neutrons. Like I said, we don't have a real dose rate neutron meter. Just CPM and that don't mean nothing to me. I am currently helping design shielding for neutrons. Water is the best but is impractical in the field. Surprisingly, Paraffin mixed with Boron has worked the best so far but wax has a low melting point and is actually flammable. I have some ideas that involve Sodium Polyacrylate and Samarium. We will see how those tests go.
Now, I will say this. Two years ago I was diagnosed with Follicular Lymphoma. After treatment, the PET scans show good. So, did this radiation contribute to that? I don't know. I also smoked cigarettes when I was younger and drank quite a bit. So, no I cannot say that radiation was the cause. Doctors will only say that radiation could be a contributing factor |
| Stargazer 40 |
Posted - 09/22/2024 : 14:55:56
I second GTS comment. I freak when I see people handling even these teaching sources. I have never touched one. I have a pair of stainless steel aquarium tongs 15" long. Perfect for moving these things around and even the foot I am away from them instead of holding in my hand or with fingers just makes me feel better. $8 on Amazon. Cheap insurance.
And yes, you're messing with some potent stuff. I envy the access but I'm glad you're doing it and not me. :-)
Oh, and I store them in a lead pig about 3" tall and inside diameter of the disc. About 3/8" thick walls. I keep those in a one foot square box centered with plastic peanuts. |
| Tony81269 |
Posted - 09/22/2024 : 13:38:08
quote:
Originally posted by GTS
Please minimize your exposures to beta. Remember Time:minimize, distance:maximize, shielding:maximize!
I hear you GTS. Just wait till next week though. I will be taking measurements in front of a 220 mCI CS-137 logging source. We wear TLD dosimeters so they check my exposure. The maximum allowable yearly for a radiation worker according to the NRC is 5 REM. My lifetime dose over 18 years is about 4.5 REM's. So, I guess I'm not doing too bad
Honesty, it's not the beta or gamma that concerns me the most. It's the neutrons. We have about 14 AmBe 5 Ci neutron sources but we do not own a real neutron dose meter. We have several that will read CPM but to me, CPM doesn't mean anything except yes it's there and it's either low or high |
| GTS |
Posted - 09/22/2024 : 13:07:47
Please minimize your exposures to beta. Remember Time:minimize, distance:maximize, shielding:maximize! |
| Tony81269 |
Posted - 09/22/2024 : 12:47:19
quote:
Originally posted by GTS
Ok, my 2 cents!
The sensor location indicator line seems correct.
I have never seen that kind of source so I don't know where the active Cs-137 is located. I would tape it to the little box facing one way and then the other and see which way seems to give believable results.
On the Cs-137 which is mostly beta which is stopped by AL, plexiglass, plastic, I would tend to keep any of these blockers out of the way just to keep the measurement clean, simple and uncomplicated. The original measured activity of that source, I would think would not have used any blockers in their original calibration. And the 800 case, I would think that the guy who calibrated it did not take the 800 plastic case apart so don't worry about that complication. Anyway, you were close in your original measurements so be happy.
Yeah, it's close but I think I will trade this source out with ones like you are talking about. I think we have some. Then I will try it vertically and pointing to the detector. I just have to figure a way to keep the thing standing up and not roll away |
| GTS |
Posted - 09/22/2024 : 12:43:15
Ok, my 2 cents!
The sensor location indicator line seems correct.
I have never seen that kind of source so I don't know where the active Cs-137 is located. I would tape it to the little box facing one way and then the other and see which way seems to give believable results.
On the Cs-137 which is mostly beta which is stopped by AL, plexiglass, plastic, I would tend to keep any of these blockers out of the way just to keep the measurement clean, simple and uncomplicated. The original measured activity of that source, I would think would not have used any blockers in their original calibration. And the 800 case, I would think that the guy who calibrated it did not take the 800 plastic case apart so don't worry about that complication. Anyway, you were close in your original measurements so be happy.
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| Tony81269 |
Posted - 09/22/2024 : 12:01:19
If you already read the above please read again. I edited it a little |
| Tony81269 |
Posted - 09/22/2024 : 11:24:16
quote:
Originally posted by GTS
And you are going to have to take the source out of the plastic box. The less stuff between the source and gm, the better.
Ok guys, I will try this again based on your suggestions. Now here is a question that I don't really know and maybe you would know.
As you are looking at the back of the meter, on the right side, it says "sensor location" and has a line and some half circle symbols. The line is approximately 0.5" from the edge of the plastic case. So, is that the location of the tube? Because that's where my measurements were taken from. See picture below.
Also, I want to show you my issue with this little check source right now. I'll also put it in a picture below. It is not thin plastic piece like some of the other check sources at work are. This is a thin piece of aluminum or other metal. I don't know how they make this particular type of check source but it is designed to be placed on a density detector inside of a logging tool. They glue it down and tape it onto the cylindrical detector. Hence the bent shape - someone has used this before. The counts from the check source on the detector are used to in some way to measure PE. I'm not a engineer. I may trade it out for the types of sources you guys are talking about. Even then, I have to figure a way to keep the thing standing vertically. Any suggestions?
Also, yes the source is in a plastic case but wouldn't that just block Beta? I also don't know when it was calibrated if they tried to shield it from Beta. On a Ludlum with a 44-6 probe there is a rotary Beta shield. Ludlum says to keep this closed when calibrating or taking dose rate measurements of gamma. I would also assume that the plastic case on the GMC-800 is blocking Beta. Am I right or wrong? Although I would imagine Beta is not really contributing very much at all with this check source.
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| GTS |
Posted - 09/22/2024 : 10:35:28
And you are going to have to take the source out of the plastic box. The less stuff between the source and gm, the better. |
| Stargazer 40 |
Posted - 09/22/2024 : 04:27:57
Spectrum Technologies where I got my sources says disc orientation makes a significant difference. The hole with sample (under label) needs to be pointed at tube so in the case you're showing it should be on edge. Also unless a certified source there's a 20% potential error in source. If it just says 5 uCi it's uncertified. If it say something like 5.386 uCi it's certified. Yours looks to be certified. |
| Tony81269 |
Posted - 09/21/2024 : 18:04:37
In my line of work, these low measurements would almost never be used. If we had a source rupture then it might be for samples of the mud. Also, when we do leak tests it could possibly be used to check for contamination. Rarely do we deal with this kind of stuff.
Our normal measurements for Pig surveys are between about 3-5 mR/h. We would also take surveys to figure a restricted area so we might read high until we get down to below 2 mR/h |
| Tony81269 |
Posted - 09/21/2024 : 17:20:00
quote:
Originally posted by GTS
Also read revision to my comment about standing on edge vs flat on cardboard.
That is a good thought. Didn't think it would make a difference but it could be more focused like that. I will give it a try but it might not be this evening. Thanks for the suggestions. I don't claim to be an expert at anything |
| GTS |
Posted - 09/21/2024 : 16:05:39
Also read revision to my comment about standing on edge vs flat on cardboard. |
| Tony81269 |
Posted - 09/21/2024 : 16:01:51
quote:
Originally posted by GTS
Using Rad Pro Calculator, assume Cs-137, there is an error in your born date. You used (M/D/YYYY) for the current date, just not for the born date. Correcting this error makes your 800 just a hair better for the close measurements.
Born D New Act
1/5/2014 3.5353
5/1/2014 3.5612
I am using Rad Pro Calculator as well. You were exactly right about my mistake. It didn't make much of a difference unless I were to go into triple digits. Then it would be closer by a hair. Thank you very much for pointing this out. Everything should be correct now |
| Tony81269 |
Posted - 09/21/2024 : 15:46:56
quote:
Originally posted by GTS
Using Rad Pro Calculator, assume Cs-137, there is an error in your born date. You used (M/D/YYYY) for the current date, just not for the born date. Correcting this error makes your 800 just a hair better for the close measurements.
Born D New Act
1/5/2014 3.5353
5/1/2014 3.5612
Crud! You are exactly right and I will have to edit this entire thing. Thank you for pointing that out |
| GTS |
Posted - 09/21/2024 : 12:17:02
Using Rad Pro Calculator, assume Cs-137, there is an error in your born date. You used (M/D/YYYY) for the current date, just not for the born date. Correcting this error makes your 800 just a hair better for the close measurements.
Born D New Act
1/5/2014 3.5353
5/1/2014 3.5612
Also is the source disk standing on edge or laying flat on the cardboard? I would think that is should be standing on edge, with the center hole where the Cs-137 is located, facing the GC-800. |
| Tony81269 |
Posted - 09/20/2024 : 20:10:11
I couldn't help myself so I went out to 5" from the source. A 3.561 uCi source at 5" should give a dose rate of 0.07 mR/h. I was able to get that very easily and it would sometimes hover back and forth between 0.07 and 0.08. I am convinced that this meter is accurate at very low dose rates.
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| Tony81269 |
Posted - 09/20/2024 : 19:27:39
Next week sometime I will pull out the bigger 220 mCI source and do some high dose tests. Similar to what I did last time with a 25ft tape measure coming from the source. I will take readings at several distances and determine if the accuracy is good at high and medium ranges |
| Tony81269 |
Posted - 09/20/2024 : 19:21:59
Well, I went out to 4". At that distance, the dose rate of a 3.561 uCi source should read 0.11 mR/h. I was able to get between 0.11-0.13 on repeats. This looks really good to me at low doses.
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| Tony81269 |
Posted - 09/20/2024 : 19:09:12
So, I decided to go a little lower. At 3" away from the 3.561 uCi source, the dose rate should read 0.197 mR/h. The closest I came was 0.21 mR/h and subsequent tries would put it in the 0.22 and 0.23 mR/h range. I do not consider this a failure by far. This is low dose accuracy and I would say is very good.
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