Elevated Geiger Counter Radiation Reading for Envelope?

[jun192022]

TL;DR Summary

Is anyone able to replicate falsely elevated Geiger counter readings by inducing a static electrical charge on a plastic bubble mailer envelope?

I previously purchased a Geiger counter (GQ Electronics GMC-600+) for a university lab and have been confused about an elevated radiation reading from the envelope the Geiger counter came in. The envelope was a USPS Priority Mail bubble mailer envelope (https://store.usps.com/store/produc...ority-mail-flat-rate-padded-envelope-P_EP14PE), and when I put the Geiger counter up to the envelope, the reading went up to about 155 CPM (0.44 µSv/hr), compared to about 40 CPM (0.11 uSv/hr) for background and 110 CPM for a granite countertop. If I held up a piece of paper between the Geiger counter and envelope, the measured radiation went down to around 130 CPM. These readings were repeated 3 separate times 15-30 minutes apart. However, when I retested the envelope a day later, I was not able to detect elevated radiation levels.

I have been a bit confused and concerned about possible radioactive contamination on the envelope falling off and spreading elsewhere. However, I also read that static charges may temporarily induce false radiation readings for pancake Geiger counters, as noted with plastic sandwich bags: https://hps.org/publicinformation/ate/q10421.html. I am wondering whether there was a static charge on the envelope, given that 1) I had put the envelope inside a plastic grocery bag earlier that day and it could have rubbed against the plastic bag, and 2) the envelope had been taped together and I had peeled some packing tape off its surface before taking the Geiger counter out.

Questions:

1 - Has anyone else had similar experiences with something like this before, and if so, with what kinds of items?

2 - Would anyone here be able to 1) induce a static charge (either through rubbing with a plastic bag or peeling off tape) on a plastic bubble mailer envelope (preferably a USPS Priority Mail bubble mailer envelope) and replicate an elevated radiation reading using a pancake Geiger counter (preferably a GQ GMC-600+), and 2) show that the elevated reading persists when a sheet of paper is inserted between the Geiger counter and envelope? I no longer have the original envelope or Geiger counter (not working at the university lab anymore), so any help to confirm that I likely did not encounter radioactive contamination would give me some peace of mind and be much appreciated!

• This is the type of envelope: https://store.usps.com/store/produc...ority-mail-flat-rate-padded-envelope-P_EP14PE

3 - How concerned should I be about this measured radiation level if there were some kind of contamination? If my readings were accurate, I calculated the potential extra yearly radiation above background as: (0.44-0.11)*24*365/1000 = 2.89 mSv/yr.

• One one hand, this is below the 5 mSv/yr occupational limit for minors and pregnant women: https://www.nrc.gov/reading-rm/doc-collections/cfr/part020/full-text.html#part020-1207
• On the other hand, it is above the 1 mSv/yr NRC exposure limit for members of the public: https://www.nrc.gov/reading-rm/doc-collections/cfr/part020/full-text.html#part020-1301
• In the worst-case scenario of contamination leading to chronic radiation exposure, an online predictor of cancer risk from radiation exposure (https://www.xrayrisk.com/calculator/calculator-recurring-studies.php) calculated that a female chronically exposed to 2.63 mSv/yr above background every year of life from age 1 to 77 (expected lifetime in US) could have a 2.866293% (1 in 35) additional lifetime cancer risk. This seems a bit high when compared to the lifetime risk of dying in a car accident of 1 in 93 (https://injuryfacts.nsc.org/all-injuries/preventable-death-overview/odds-of-dying/data-details/)?

 

[Alex A]

It's common for static charges to pull dust, including radon decay products from the air. Turning off a CRT TV, in the days before they were antistatic coated, and then wiping the screen with a tissue and measuring it with a mica widow geiger counter and plotting the decay curve was something you could do. That may be part of what is going on.

 

[Vanadium 50]

First, a $50 radiation detector is way, way, way inadequate to do health physics. If you have health concerns, you need to use a real, calibrated survey meter, the kind health physics use. These cost an order of magnitude more than what you have.

Second, sure it's possible that piece of plastic collected radon or radon daughters on the trip. Especially if it spent time in a basement somewhere. I've seen that happen. Possible, but is it likely? Well, I'd say it's more likely that your meter is having a bad day.

Finally, I would be very surprised if your meter is actually a Geiger counter. It is far more likely to use another principle of operation entirely.

 

[gleem]

Until you can duplicate what you observed we can only speculate and of course let our imaginations run wild. As a medical physicist and radiation safety officer I have observed unexplainable radiation readings significantly higher than background when using a GM counter. Real readings are always reproducible.
These survey meters push the limits of sensitivity for determining contamination and when something suspicious occurs one must use other suitable calibrated detectors and methods to determine a reasonably accurate quantitative estimate of contamination.

Concerning removable contamination, the Nuclear Regulatory Commission rules state you should wipe the suspicious area (recommended 100 sq-cm) or object with a damp swab like a lens wipe for eyeglasses. These also contain alcohol ( squeeze out excess alcohol) which is better at cleaning a surface and removing contamination. Determine the removable activity. Then place the wipe near the detector. It should be less than 100 disintegrations per minute. Determination of dpm from counts per minute is no small task. GM detectors are very inefficient for various reasons and do not discriminate gamma from charged particles. Since detectors only register what passes through them you must also determine the fraction of those particles that are missed due to being absorbed by the wipe or just missing the detector.

If you can repeat your observation then take a wipe to a local medical center. There should be an RSO who might be willing to help you or refer you to a commercial lab if it is that important. Years ago these labs charged $50 per wipe.

One final word with regards to the use and interpretation of GM radiation dose equivalent readings. They only apply to gamma and x-radiation and only apply to energies that are likely to penetrate deep into the body approximately greater than about 80 KeV. So you have to know the radiation type to interpret the reading. GM counters give you basically a heads-up to the existence of possible levels of radiation.

 

[Vanadium 50]

To add - while the meter apparently reads in Sieverts, there is no way to go from counts to Sieverts without knowing what kind of radiation you have. (Assuming there is any at all)

Next, taking the results at face value, this is 2-3x background. There are likely many other comparable sources in your environment. Doctor x-ray you? Take a plane trip? Married? Cook on the granite countertop you mentioned? Like bananas?

Finally, use common sense. If a year's exposure looks high to you, don't spend a year sleeping with the envelope in question.

 

[jun192022]

It's common for static charges to pull dust, including radon decay products from the air. Turning off a CRT TV, in the days before they were antistatic coated, and then wiping the screen with a tissue and measuring it with a mica widow geiger counter and plotting the decay curve was something you could do.

I understand that static charges could potentially lead to false readings, but I am unclear as to whether such a false reading would still be expected if a sheet of paper were to be placed between the Geiger counter and source of the static charge.

If you have access to a pancake Geiger counter, would you be able to run an experiment with it on a plastic bubble mailer envelope which has an induced static electric charge (such as through rubbing with a plastic grocery bag or unpeeling tape on its surface)? While I suspect the static charge hypothesis is likely, I do not currently have a Geiger counter to actually prove that a static charge can be induced on a plastic bubble mailer envelope significant enough to cause a false radiation reading.

 

[jun192022]

First, a $50 radiation detector is way, way, way inadequate to do health physics. If you have health concerns, you need to use a real, calibrated survey meter, the kind health physics use. These cost an order of magnitude more than what you have.

Second, sure it's possible that piece of plastic collected radon or radon daughters on the trip. Especially if it spent time in a basement somewhere. I've seen that happen. Possible, but is it likely? Well, I'd say it's more likely that your meter is having a bad day.

Finally, I would be very surprised if your meter is actually a Geiger counter. It is far more likely to use another principle of operation entirely.

Thanks for your response. I don't know if you are familiar with the GMC-600+, but it's a pancake Geiger counter (measures alpha, beta, gamma) and costs more than $300. The thing that makes me confused is that aside from the envelope, the GMC-600+ seemed pretty accurate for measuring background radiation and picking up radiation from a granite countertop. I also understand that static charges and/or radon daughters could potentially lead to false readings, but I am unclear as to whether such a false reading would still be expected if a sheet of paper were to be placed between the Geiger counter and source of the static charge.

If you have access to a pancake Geiger counter, would you be able to run an experiment with it on a plastic bubble mailer envelope which has an induced static electric charge (such as through rubbing with a plastic grocery bag or unpeeling tape on its surface)? While I suspect the static charge hypothesis is likely, I do not currently have a Geiger counter to actually prove that a static charge can be induced on a plastic bubble mailer envelope significant enough to cause a false radiation reading.

 

[Rive]

I would be very surprised if your meter is actually a Geiger counter.

Well, at least it has a (cheap) Geiger-tube.

These cheap meters are not real instruments and are barely adequate for measuring guessing background radiation, but at the end they'll still show something real.

 

[jun192022]

Until you can duplicate what you observed we can only speculate and of course let our imaginations run wild. As a medical physicist and radiation safety officer I have observed unexplainable radiation readings significantly higher than background when using a GM counter. Real readings are always reproducible.
These survey meters push the limits of sensitivity for determining contamination and when something suspicious occurs one must use other suitable calibrated detectors and methods to determine a reasonably accurate quantitative estimate of contamination.

As I mentioned, I do not currently have the original Geiger counter since I am no longer working in the university lab. I suspect the static charge hypothesis is likely. However, I wanted to see if anyone else who has a pancake Geiger counter would be able to actually do an experiment to prove that a static charge can be induced on a plastic bubble mailer envelope significant enough to cause a false radiation reading.

If you have access to a pancake Geiger counter, would you be able to run an experiment with it on a plastic bubble mailer envelope which has an induced static electric charge (such as through rubbing with a plastic grocery bag or unpeeling tape on its surface)?

 

[Rive]

If you have access to a pancake Geiger counter, would you be able to run an experiment with it on a plastic bubble mailer envelope which has an induced static electric charge (such as through rubbing with a plastic grocery bag or unpeeling tape on its surface)?

That won't be enough. A basement with high radon concentration is also needed, otherwise the static charge will attract nothing relevant.

This case is lot more complicated and sensitive than what a half-baked attempt would be able to catch.
Your explanation 'feels' right, but to prove it is anything but simple...

 

[jun192022]

That won't be enough. A basement with high radon concentration is also needed, otherwise the static charge will attract nothing relevant.

This case is lot more complicated and sensitive than what a half-baked attempt would be able to catch.
Your explanation 'feels' right, but to prove it is anything but simple...

At the time of the elevated reading, I was not in a basement. However, I don't know what the radon concentration was.

For my own physics understanding, is it the static electric charge itself, or the radon daughters which are attracted to the static charge, which can lead to a false radiation reading on the Geiger counter? The information on the Health Physics Society page seemed to suggest that static charges are able to induce false readings on their own: https://hps.org/publicinformation/ate/q10421.html

 

[Vanadium 50]

I was not in a basement.

But had the envelope been in a basement?

 

[russ_watters]

Finally, use common sense. If a year's exposure looks high to you, don't spend a year sleeping with the envelope in question.

That's not enough. You'd have to wear it 24x7...and even then I'd think half the radiation is emitted away from you.

 

[jun192022]

But had the envelope been in a basement?

Not in the 3-4 days before the elevated reading (it had been on the 3rd floor of a multistory building). Before that, it had been in a mailbox outside, which was not found to have any elevated radiation readings.

 

[jun192022]

That's not enough. You'd have to wear it 24x7...and even then I'd think half the radiation is emitted away from you.

That is assuming that if there were radioactive contamination, it would have remained on the envelope. However, it could hypothetically have been possible that contamination in a powder form could have fallen off, potentially be inhaled and not easily excreted by the body, and be of a long-lived isotope which could lead to chronic exposure. While I suspect the static charge hypothesis is more likely, I still have not yet been able to prove that it is possible to induce a static electric charge on a plastic bubble mailer envelope significant enough to induce an elevated reading on a pancake Geiger counter (whether due to attracting radon decay products or due to the electric field itself).

 

[russ_watters]

That is assuming that if there were radioactive contamination, it would have remained on the envelope. However, it could hypothetically have been possible that contamination in a powder form could have fallen off, potentially be inhaled and not easily excreted by the body, and be of a long-lived isotope which could lead to chronic exposure.

Well that's quite a reach. It requires that the powder be so loosely bound to the envelope that it could come off in such a way that enables you to inhale all of it yet not have been released during its handling in the postal system (and yet also well behaved enough to survive days of your handling and measurement). You would have trouble achieving that if you purpose built a device to do the job. And even then the risk would only be on par with an annual chest x-ray. You are reaching hard for a risk that does not exist.

 

[gleem]

However, it could hypothetically have been possible that contamination in a powder form could have fallen off, potentially be inhaled and not easily excreted by the body, and be of a long-lived isotope which could lead to chronic exposure. While I suspect the static charge hypothesis is more likely, I still have not yet been able to prove that it is possible to induce a static electric charge on a plastic bubble mailer envelope significant enough to induce an elevated reading on a pancake Geiger counter (whether due to attracting radon decay products or due to the electric field itself).

As I said before with regard to non reproducible events.

Until you can duplicate what you observed we can only speculate and of course let our imaginations run wild.

The next question is when you receive a similar envelope at your home, how will you handle it?

 

[jun192022]

You are reaching hard for a risk that does not exist.

While I agree that the likelihood is very low and probably trivial, it also cannot be said to be zero with absolute certainty. Given that I have no idea what was causing the elevated radiation reading, I calculated based on a hypothetical worst-case scenario to establish an upper bound of risk.

 

[jun192022]

As I said before with regard to non reproducible events.
The next question is when you receive a similar envelope at your home, how will you handle it?

Interestingly, apparently multiple other people have been able to reproduce elevated radiation readings with balloons by rubbing them, waiting awhile for radon daughters to collect, then testing with a Geiger counter:

• I also found a science demonstration with instructions on Harvard's website on how to reproduce this phenomenon with a balloon: https://sciencedemonstrations.fas.harvard.edu/presentations/radons-progeny-decay

However, I have not read or heard of anyone observing this phenomenon before with a plastic bubble mailer envelope, so I am curious whether anyone here has witnessed this before or would be able to do a simple experiment. Such an experiment would entail inducing a static charge on the plastic bubble mailer envelope (potentially by rubbing with a plastic grocery bag or peeling tape off its surface), waiting for awhile for radon daughters to collect, then testing the envelope with a Geiger counter.

 

[gleem]

The decay measured on the balloon experiment does not have a recognizable half-life because they are measuring all radiations including gammas from Radon and its decay products i.e., Po218, Pb214, Bi214, Po214 simultaneously. If you want a half-life of one of these isotopes you have to identify the radiation produced by that isotope and only count it. This chain of decay ends up on Pb210 which has a 22.3 yr half-life and thus will have a very small activity. When Rn222 mostly decays in about 5 weeks each Rn222 will have produced one Pb210 and it will have increased the amount of Pb210 to nearly its maximum activity whereupon it will slowly decay to Bi210

 

[Vanadium 50]

My experience is that items with radon contamination "clean up" after a day or two. I think the daughters leave the environment before the decay chain is complete.

 

[jun192022]

My experience is that items with radon contamination "clean up" after a day or two. I think the daughters leave the environment before the decay chain is complete.

That would be consistent with the transiently elevated readings I obtained, and the fact that some radon daughters emit beta radiation could explain why the elevated reading I obtained persisted when a sheet of paper was placed between the Geiger counter and envelope. However, for this particular situation, this is still speculation given that no one (as far as I have read and researched) has done a test similar to the balloon experiment with a plastic bubble mailer envelope.

 

[jun192022]

The decay measured on the balloon experiment does not have a recognizable half-life because they are measuring all radiations including gammas from Radon and its decay products i.e., Po218, Pb214, Bi214, Po214 simultaneously. If you want a half-life of one of these isotopes you have to identify the radiation produced by that isotope and only count it. This chain of decay ends up on Pb210 which has a 22.3 yr half-life and thus will have a very small activity. When Rn222 mostly decays in about 5 weeks each Rn222 will have produced one Pb210 and it will have increased the amount of Pb210 to nearly its maximum activity whereupon it will slowly decay to Bi210

Yeah, it's fascinating to observe since there are several short-lived radioisotopes in the radon decay chain. It's also interesting to see that this experiment with the balloon has been replicated by multiple people, so in theory it seems it would not be too difficult to replicate with a plastic bubble mailer envelope.

 

[Rive]

My experience is that items with radon contamination "clean up" after a day or two. I think the daughters leave the environment before the decay chain is complete.

I too think it's more of an evaporative 'half-life' than nuclear.

 

[jun192022]

I too think it's more of an evaporative 'half-life' than nuclear.

Out of curiosity, what would cause it to be more of an evaporative effect, given that radon daughters are solids and not gas? Would the radon daughters fall off from items with radon contamination or get onto other items in the surrounding environment?

 

[Vanadium 50]

If you have one atom of a substance, it is not solid. It is not anything. Its phase is a property of bulk matter, not individual atoms.

 

[gleem]

I had forgotten that for Radon decay the daughter products will come into equilibrium (secular equilibrium) with an apparent decay rate equal to Radon which will be 3.8 days. So the reduction activity must be due to something other than radioactive decay. The Po, Pb, and Bi isotopes can't decay until they are formed and that depends on the decay rate of Radon.