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TL;DR: I'd like someone to run an experiment to prove that it is possible to induce a static electric charge on a plastic bubble mailer envelope (such as through rubbing with a plastic grocery bag or peeling packing tape off its surface) which is significant enough to attract radon decay products and induce an elevated reading on a pancake Geiger counter. I do not currently have the Geiger counter mentioned below in this post. Thanks!

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/product/shipping-supplies/priority-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 - 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!

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

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)x24x365/1000 = 2.89 mSv/yr.

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  • $\begingroup$ I really love this topic but I've never seen this site used to request people to run experiments fyi. I think you've answered your own question with the link, the static electricity of the bag caused the elevated reading. $\endgroup$
    – dllahr
    Dec 19, 2023 at 10:14
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    $\begingroup$ @dllahr While I read that statically charged plastic sandwich bags can cause elevated readings, I have not read or heard of anyone finding the same to be the case for plastic bubble mailer envelopes. I suspect the static charge hypothesis to be likely, but I still not 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 the electric field itself or attracting radon decay products). $\endgroup$
    – jun192022
    Dec 20, 2023 at 9:26
  • $\begingroup$ Can you help me understand how you convert from CPM to µSv/h? $\endgroup$
    – ntoskrnl
    Dec 22, 2023 at 22:45
  • $\begingroup$ @ntoskrnl The GQ GMC-600+ automatically shows both CPM and uSv/hr. I believe the default setting is 350 CPM per 1 uSv/hr. $\endgroup$
    – jun192022
    Dec 23, 2023 at 9:34
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2 Answers 2

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Electrostatically charged objects will attract natural radioactive ions from air and this can easily be measured with a Geiger counter, but the health risks are usually negligible. It is easy to show that a plastic envelope can be electrostatically charged, so it is not necessary to do an experiment to know that the envelope will pick up radioactive ions from the air.

Radioactivity on Plastic Objects

If on a dry day you rub a balloon against your hair to charge it up, and then hang itfor an hour from the ceiling, it can attract enough radioactive ions so that when deflated it can produce a signal in a Geiger counter one or two orders-of-magnitude greater than background. This is discussed in Thomas Walkiewicz's 1997 paywalled article on "The hot balloon (not air)" and on John Iovine's non-paywalled webpage "Radon nuclides captured in ambient air by electrostatically charged balloon."

Similarly, Cowie and Walkiewicz's 1992 article "Radioactive Ball" showed that rubber balls used in hand or racquet ball become electrically charged by friction during play and can collect significant numbers of radioactive ions producing Geiger signals well above background.

A plastic mailing envelope can easily build up a static charge if the humidity is low. In fact, static on plastic mailing wraps or envelopes has been known to build up to levels sufficient to damage postal sorting machinery. Just to check, I rubbed one against my hair and the charge was sufficient to stick the envelope to the ceiling. If it has enough charge to stick to the ceiling, it will attract radon progeny ions from the air.

It is worth noting that you can also get electrostatically charged and according to Stahther, it is this charge on you, not the charge on nearby objects, that can most increase your radon progeny skin dose rate. Regularly sitting in a static generating plastic chair could increase your charge and dose far more than a transiently charged and radioactive envelope. (As noted by @Rob, this furniture effect is mentioned in the accepted answer to "Why is my dryer radioactive?".)

Health Effects

Radioactivity from a single envelope is not a health concern. As you note, the radioactivity disappeared within a day, so the potential yearly dose from your envelope is not 2.89 mSv/yr, but 2.89/365 = 8 µSv/yr or less. (I'd actually expect the radioactivity to disappear within a few hours, given typical lifetimes for static electricity and the half-lives of radon progeny.) Your whole-body dose – which is what the 5 mSv/yr and 1 mSv/yr exposure limits refer to – will also be much less because you measured the dose rate close to the envelope, but the dose averaged over your whole body is much smaller because of inverse square law and range effects.

As @ntoskrnl notes in their answer, the radon progeny attracted to the envelope are already in the local environment, so concentrating them on the envelope may not make all that much difference in your total dose. A CERN study measured reduced radon progeny near a TV because the ions were swept away by either being repelled or attracted to the screen. Since inhalation produces the greatest risk from radon decay products, this could even conceivably reduce your dose.

In any event, the radiation risk from electrostatically charged objects could only be significant if you are constantly exposed to them in close proximity. Back when computer monitors and televisions were cathode ray tubes (CRT), their screens would would be electrically charged and collect dust and ions. One 2002 study reported that a worker who spent 6 hours/day for 200 days/year working in front of a CRT could possibly receive an annual dose close to 2 mSv, although earlier studies referred to in the article seem to think it was less of a problem.

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  • $\begingroup$ Thanks so much for the very detailed response! Just to clarify, when you stated you were able to induce a static charge in an envelope and get it to stick the ceiling, was the envelope a plastic bubble mailer envelope (the kind with plastic on the outside and bubble wrap on the inside)? In a similar vein, the link about static disrupting the USPS mail service mentions mailer wraps, but does not specify whether those had plastic on or paper on the outside - would you be able to provide more details/resources specific to plastic bubble mailer envelopes? Thanks again! $\endgroup$
    – jun192022
    Dec 29, 2023 at 8:44
  • $\begingroup$ @jun192022 I used a Canada Post "8 1/2 x 11 Poly Bubble Mailer" very similar to your envelope. The USPS limits for static buildup are specifically for polywrap (polyethylene, see 2.1.8 of "USPS-T-3204 - Test Procedures for Automatable Polywrap Film"). Paper is much less prone to triboelectric charging. $\endgroup$ Dec 29, 2023 at 17:07
  • $\begingroup$ Great, thank you for the additional resources! I saw in the USPS test procedure guidelines that materials used in polywrap must be found to have a static charge of less than 2 kV on testing. Given that there is this required limit on how much static charge a plastic bubble wrap mailer envelope can potentially build up, would this mean it would be less likely for such a plastic envelope to build up enough charge to attract sufficient amounts of radon progeny to cause an elevated Geiger counter reading? $\endgroup$
    – jun192022
    Dec 30, 2023 at 19:32
  • $\begingroup$ If rubbing the envelope against (dry) hair on a dry day charges the envelope enough so it attracts your hair, then it is charged enough to attract ions. $\endgroup$ Dec 30, 2023 at 22:09
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It is well documented that electrically charged items (such as plastics that have picked up a static charge) can collect a measurable amount of radioactive atoms from the environment. They are mostly short lived isotopes in the radon decay chain. Radon is a naturally occurring radioactive gas that is produced in soil. When radon atoms decay in the air, the daughter products will be ionized and will be attracted to electrically charged surfaces. The measurable daughter nuclei are fairly short lived, and will decay to more stable isotopes over a few hours. See this video by Matthias Wandel where he explores this phenomenon, and this video by Simons Nuclear Chemistry where he measures the phenomenon in a university lab setting.

As for the measured radiation level, it is not at all trivial to convert a count rate to a dose rate. See this video by Simons Nuclear Chemistry where he compares radiation measurement devices. A Geiger tube counts the number of ionization events inside the tube, while radiation dose is the amount of energy deposited inside tissue multiplied with a fudge factor that depends on the type of radiation. It is impossible to go from count rate to dose rate without knowing more details about the situation. A Geiger tube is not sensitive to certain types of radiation, and it cannot differentiate between different energy levels. It also has a different geometry and location than a human body. The dose rate display on the meter is probably calibrated for a uniform background radiation level, so even if it was otherwise accurate, it would be incorrect to interpolate a short term reading from a small object to the equivalent background level over an entire year.

The amount of radioactive material collected on an envelope is measurable but insignificant, because it consists of radioactive material that would be present in the environment anyway, and the measurable isotopes are short lived. The dose rate displayed on the Geiger counter is not accurate.

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  • $\begingroup$ Thanks for the detailed response! Radon daughters seem likely, given that some radon daughters emit beta radiation, consistent with the elevated readings I got through a sheet of paper. It seems multiple people have been able to induce a static charge on a balloon, attract radon daughters, and reproduce elevated radiation readings on a Geiger counter: sciencedemonstrations.fas.harvard.edu/presentations/…, youtube.com/watch?v=UAulEyCeLwY However, so far I have not read/heard of this being observed with a plastic bubble mailer envelope. $\endgroup$
    – jun192022
    Dec 23, 2023 at 18:43
  • $\begingroup$ If you or anyone else here has access to a Geiger counter, would anyone be able to try an experiment? Such an experiment could involve: 1) Checking a plastic bubble mailer envelope and balloon (experimental control) with a Geiger counter to establish a background radiation level for both items. 2) Inducing a static charge in both the plastic envelope and the balloon and hanging/suspending both items so they are not touching the ground or other objects. 3) Waiting ~30 minutes to allow radon daughters to settle on the envelope and balloon. 4) Retesting both items with a Geiger counter afterward. $\endgroup$
    – jun192022
    Dec 23, 2023 at 18:47

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