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hooliganbear
USA
2 Posts |
 Posted - 10/31/2024 : 14:03:57
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Hello there I am completely new to this and new to this form. I have purchased the GQGMC Dash 800 geiger counter. I work for the railroad and I'm working. On a job that takes empty cars to San Onofre nuclear power Plant in San Onofre, California, and the nuclear plant has been decommissioned so they are dissembling the nuclear plant and they are filling the rail cars with material from the nuclear plant and some of the cars have radioactive placard's on the rail cars. I purchased the geiger counter for my personal safety to measure the area and cars when I go there. My geiger counter went crazy the other night and had readings of 1500 CPM 0.98 mR/h & 15.10 uSv/h. Now, according to this little card that comes inside the box of the geiger counter labeled nuclear radiation safety, guide all of those numbers that I just posted in this message are all dangerously high, according to the readings on the geiger counter compared to the safety guidelines. I'm being told by my company I work for along with the nuclear plant people which is actually the Edison power company that these numbers are safe and are within federal guidelines to work around and transport. Can anybody clarify that these are safe levels. Because I have tried to research and figure out. If actually, these numbers are safe or not safe and I guess I'm not smart enough to figure it out in some desperate need of help here. Thank you for any help that you can give me.
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Eric Von Theumer |
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| Reply #1
ullix
Germany
1171 Posts |
Posted - 11/01/2024 : 00:09:25
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Eric, I see two issues behind your post:
1) the observation of an unrealistic reading of GMC-800 Geiger counter
2) a question regarding the danger of any radiation values
Unrealistic readings often result from the "FET" setting (stands for Fast Estimate) due to the algorithm used for it. Switch this to OFF, i.e. set it to 60 (sec).
Possible, but less likely, is electric interference from nearby machinery, like lifts, welding, airco, etc.
Re the danger there is not an easy answer. It is regulated world-wide, but the regulation can be drastically different. There is even credible science suggesting that some low radiation could actually be beneficial for your health (key word: hormesis, see: https://sourceforge.net/projects/geigerlog/files/Articles/GeigerLog-Calibration%20Guidance-v1.5.0.pdf/download ).
The difference in regulation between USA and Germany may give some insight into the relevance of "critical levels". For an initial reading I suggest the chapters "Occupational Radiation Limits" and following from the GeigerLog Manual (https://sourceforge.net/projects/geigerlog/files/GeigerLog-Manual-v1.5.0.pdf/download)
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| Reply #2
GTS
USA
38 Posts |
Posted - 11/02/2024 : 12:33:18
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My 2 cents:
Based on your description and guessing at a few additional details.
1) USA:NRC limit for member of public: 100 mR/yr. Sounds like you are in the under 100 mR/yr group not requiring special training or reporting requirements to the NRC.
See: https://www.nrc.gov/reading-rm/doc-collections/cfr/part019/part019-0012.html
2) USA:NRC limit for Occupational worker (nuclear) Whole Body TEDE: 5000 mR/yr
3) First reading: 1500 cpm/960=1.56 mR/h,
Second reading: 0.98 mR/h,
Third reading: 15.1 uSv/h=1.51 mR/h
so assume your exposure is about 1.5 mR/hr.
4) Assume you will spend .05 hours next to each RR car and there are 5 RR cars and you do this pickup 20 times/year
5) Assume you have not used up the yearly allowances of 100 or 5000 mR and are well below those limits.
Answer: .05 hrs * 5 RR cars * 20 Qt/yr * 1.5 mR/hr = 7.5 mR/yr
You are 7.5% of the public limit and 0.15% of the Occupational worker limit. So you are "safe" under these assumptions.
What does the GMC-800 dosimeter feature say is your total mR dose so far? |
Edited by - GTS on 11/04/2024 18:53:50 |
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| Reply #3
Tony81269
USA
68 Posts |
Posted - 11/10/2024 : 13:39:30
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GTS,
Here is an example Public Dose Assessment form that the NRC gave me to determine what the outside of one of our field offices was. I think it goes along with what you are saying.
Anthony
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Edited by - Tony81269 on 11/10/2024 13:40:13 |
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| Reply #4
Tony81269
USA
68 Posts |
Posted - 11/10/2024 : 13:46:24
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Quick answer to the main question -
No, you are not in any danger. I would urge everyone who buys one of these to thoroughly understand what a high dose of radiation is. These things will give off alarms at very low levels. I have my alarms turned off.
I would really hate if people got freaked out over uranium glass or something |
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| Reply #5
GTS
USA
38 Posts |
Posted - 11/11/2024 : 11:51:12
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Hi Tony81269,
Good find.
According to the NRC:
1) The 2mR/hr limit is a check that should be included.
2) Background should be excluded. It's very small if you use the GQ GMCMap app which has it at about 0.12 uSv/hr or 0.012 mR/hr average near SONGS.
Other things to consider:
1) No Neutron radiation reading was taken. I wonder what it could be at the RR cars.
2) Then there is the question of uncalibrated/uncompensated GMC machines. Using a uncompensated GM counter, especially a very small one, to quantify an accurate radiation measurement is not recommended. Readings using these small tubed GM detectors tends to overestimate the readings. Instead of something like 1.5 mR/hr the more accurate reading could be something like 1/2 of that.
3) Your company and Edison say it's safe according to federal guidelines. I assume they can back this up with data and calculations which would be nice to see. Are they willing to show you that info, which would include things like the "Public Dose Assessment (PDA)" form from above?
NRC limits:
https://www.nrc.gov/reading-rm/doc-collections/cfr/part020/part020-1301.html?form=MG0AV3 |
Edited by - GTS on 11/14/2024 13:59:34 |
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Levels DANGEROUS???
