Radon progeny content in activated charcoal canisters

[Paultx]

TL;DR Summary

Radon progeny in activated charcoal canisters

Hello everybody! I am writing to you because I am worried with the content of radon progeny inside standard activated charcoal canisters used for radon measurements.

In 2011 I was working in a laboratory that was measuring radon with activated charcoal canisters, and they bought an oven that I had to use in order to reset approximately 200 canisters already used for radon gas measurements, heating them with the oven.

The oven was inside a completely closed room (the windows were also closed). My boss told me that I had to heat them in the oven for a certain period of time, and he told me that the oven temperature had to be kept constant around a certain value.

Since the oven's analogue thermometer was inside the oven, to verify that the temperature was always the same, every 2 or 3 minutes I would open the oven door to look at what the analogue thermometer was reading.

I think the problem here is with the radon progeny produced after the radon decays, which I suppose must be trapped inside the charcoal, and when heating the canisters in the oven, I think all the radon progeny left the canisters and I possibly breathed them. I don't know how many radon progeny there are in each of the canisters, and since I had to reset about 200 canisters, perhaps this was dangerous.

So, I would like to know approximately how many radon progeny there are in each canister already used, because I think this is crucial in this matter, and I would also like to know if I have an increased risk of lung cancer.

Thank you very much in advance for your help on this matter

 

[mfb]

Most likely there was no relevant radiation dose.

* The laboratory had a radiation safety expert who wouldn't have accepted this if there were any relevant dose.
* The canisters won't capture much radon.
* All the decay products of radon-222 are short-lived (<1h) except lead-210 (half life of 22 years) and its indirect decay product polonium-210 (138 days). Lead and polonium don't become airborne easily.

 

[Paultx]

The lab actually belongs to a university, and they had never done radon measurements before. The 200 canisters that I heated in the oven, which they bought new for the occasion, were the first canisters they had ever measured radon with. The detector they used to measure the activity of the canisters was a gamma scintillator, which is supposed to measure the activity of radon progeny. And in theory, by heating the canisters in an oven for a certain amount of time, you can reset the canisters, so that the radon progeny should have left the canisters after heating them to a high temperature.

A few days before I heated the canisters, my boss, who was a professor, was talking to a lab technician, and when the technician told my boss that each canister actually has a huge surface area to absorb radon by Van der Waals forces, my boss replied: Do you have moral problems?

Also, one day when I was heating a large number of canisters, I opened the room door where the oven was, and when my boss saw it open he got angry, saying that I should not open the door again or else he would fire me. I find these things worrying, because they had never done radon gas measurements before, and they bought the oven for the occasion, without thinking about the possible consequences of the procedure.

 

[gleem]

The progenies as @mfb noted are not a problem since the temperature likely never exceeded 100 °C. We cannot determine how much Radon was present when you heated the canisters. Do you know if the canisters were even held for some time so that the activity decayed before they were heated? Probably most canisters were negative or very had low activity since often local regulations required a radon test when a house was sold and people tend to be over-concerned about radon in their homes even though it was unlikely radon was a problem.

Even though the windows were not opened, I am sure there was ventilation probably at least three air exchanges per hour. It is doubtful that any activity in the room was more than the four picocuries/liter ( 0.15 disintegration per second) per liter) the EPA says is acceptable in a habitable enclosure.

Let me try to assuage your concern. What is the Radon level in your house? Even if it is very low, for example, 0.1 pCi/L (the U.S. average is 1.3 pCi/L), living in it 16 hours a day, seven days a week for 13 years, you will inhale at a rate of 6L of air per minute (ave. adult) 2,725,632 pCi the total contents of perhaps many thousands of canisters that you may have baked.

 

[berkeman]

* The laboratory had a radiation safety expert who wouldn't have accepted this if there were any relevant dose.

The lab actually belongs to a university,

So @Paultx -- was your university's safety department involved in this setup/procedure? If not, why not?

 

[Paultx]

So @Paultx -- was your university's safety department involved in this setup/procedure? If not, why not?

The university's safety department had no knowledge of what was going on there. I guess the reason is that my boss didn't give them any information.

 

[Paultx]

The progenies as @mfb noted are not a problem since the temperature likely never exceeded 100 °C. We cannot determine how much Radon was present when you heated the canisters. Do you know if the canisters were even held for some time so that the activity decayed before they were heated? Probably most canisters were negative or very had low activity since often local regulations required a radon test when a house was sold and people tend to be over-concerned about radon in their homes even though it was unlikely radon was a problem.

Even though the windows were not opened, I am sure there was ventilation probably at least three air exchanges per hour. It is doubtful that any activity in the room was more than the four picocuries/liter ( 0.15 disintegration per second) per liter) the EPA says is acceptable in a habitable enclosure.

Let me try to assuage your concern. What is the Radon level in your house? Even if it is very low, for example, 0.1 pCi/L (the U.S. average is 1.3 pCi/L), living in it 16 hours a day, seven days a week for 13 years, you will inhale at a rate of 6L of air per minute (ave. adult) 2,725,632 pCi the total contents of perhaps many thousands of canisters that you may have baked.

Hi everybody and thank you for your replies. The temperature at which I had to set the oven was 180 ºC, and some of the canisters were used to measure radon gas concentrations inside underground caves.
The canisters were left to rest, but they were all sealed with insulating tape, for over a month until I heated them in the oven.
I just found this document with more information on this matter (Radon adsorption in charcoal):
https://pmc.ncbi.nlm.nih.gov/articles/PMC8122700/

 

[gleem]

The university's safety department had no knowledge of what was going on there. I guess the reason is that my boss didn't give them any information.

How do you know this? In what department was this activity performed? What was the professional background of your boss?

Hi everybody and thank you for your replies. The temperature at which I had to set the oven was 180 ºC, and some of the canisters were used to measure radon gas concentrations inside underground caves.
The canisters were left to rest, but they were all sealed with insulating tape, for over a month until I heated them in the oven.

Holding the canisters for more than a month would have reduced the Radon activity continued therein by about 500 to 1000 times, depending on the actual time. The Nuclear Regulatory Commission does exempt from licensing certain quantities of radioactive materials. I believe nCi amounts of Radon fall in that category. Caves may contain concentrations of 50 times that of houses but canisters probably were still exempt.

My criticism of your boss and his operation is keeping it a secret from the RSO (if that is true) and his not explaining the lack of need to have special radiation precautions or procedures since you are dealing with radioactive material even in very small quantities.

Having been an RSO at a large teaching hospital I required knowledge of the use of any radioactive materials and signed off on its use since it would be my butt on the line if regulations were not properly followed.

My last question is why now after 13 years is this an issue?

 

[Paultx]

How do you know this? In what department was this activity performed? What was the professional background of your boss?

My boss, who is a nuclear physicist in the nuclear physics department, told the lab technician that there was no danger and that there was no need to report it to the university's health department. This is what the technician told me. Actually there is no RSO at this university, but there is a health safety department.

My last question is why now after 13 years is this an issue?

This has always been a concern of mine, but I had never tried to find out to what extent my health might have been in danger, or not. I suffered from the ostrich effect. Over the years this concern has grown, and that is why I have posted on this forum.

 

[gleem]

My boss, who is a nuclear physicist in the nuclear physics department, told the lab technician that there was no danger and that there was no need to report it to the university's health department. This is what the technician told me. Actually there is no RSO at this university, but there is a health safety department.

What was your role at this university? How long did you perform the

I suspect this university is not in the US. In the US a designated Radiation Safety Officer must be named if licensed quantities of radioactive material are used, whether in universities, hospitals, or private companies. It is an NRC requirement and if a state regulates its own use of radioactive material it must follow the NRC rules.

This has always been a concern of mine, but I had never tried to find out to what extent my health might have been in danger, or not. I suffered from the ostrich effect. Over the years this concern has grown, and that is why I have posted on this forum.

I have worked with people who would not accept what is known as levels of acceptable risk, i.e., any radiation exposure is too much.

In post 4 I tried to tell you that the probable exposure from normal environment Radon concentrations is far larger than that which you might have been exposed to at your work.

 

[Paultx]

I wrote to 'Health Physics Society' about this matter, and that's what they answered me by email:

Thank you for your question. It sounds like you had a challenging work situation! Based on the information you provided, it is very unlikely that this exposure caused any increase in your baseline lung cancer risk. We have provided further explanation below and hope this helps reduce your worries about this exposure.

Charcoal canisters such as the ones you described are commonly used for passive measurements of radon gas. You may be familiar with the mechanism – radon diffuses into the open canister, adheres to the charcoal during the exposure period, and then is sealed into the canister prior to counting by the laboratory. This process is time sensitive because radon is constantly undergoing radioactive decay in addition to desorption from the charcoal, meaning that the radon concentrations in the charcoal canister decrease over time.

The “effective half-life” of radon on charcoal canisters has been characterized and is approximately 24-31 hours depending on the specific environmental conditions (humidity, etc) (Maier et al 2021). This means that, once the canister is opened and counted in the laboratory, the concentrations in the canister will be at equilibrium with the laboratory environment after a few days regardless of how high the concentrations were in the homes that were measured.

Baking the charcoal canisters is another standard laboratory practice to remove radon gas and effectively “reset” the detectors for another use.

While it sounds like the conditions under which you were instructed to bake the canisters were strict and even adversarial, we hope it provides you a measure of comfort that many laboratories use this method routinely and safely. One key reason that this method is considered safe (in addition to the short effective half-life described above) is that the amount of radon on the canisters is small and any potential inhalation exposure is short term, while the risk from exposure to radon is based on long term (many years) exposure to elevated concentrations.

To provide a little more context on radiation dose and risk, radon is a noble gas, meaning that you breathe it in and back out again. Radon gas is very unlikely to interact or deposit radiation dose in the body. The risk of lung cancer from exposure to radon is primarily due to inhalation of radon’s short-lived radioactive decay products, isotopes of lead, bismuth, and polonium. In homes and workplaces, these short-lived decay products are typically present in the air wherever there is radon gas, but in a scenario like you’re describing, the radon released from the charcoal filters during baking would be nearly pure or “fresh,” with very low levels of decay products. This means that the potential radiation dose and risk would be correspondingly low as well.

Your concern about radon exposure is understandable given the amount of information about lung cancer risk and radon, and it is worth noting that the largest component of background radiation dose to the average person (outside of medical exposures) is due to radon (NCRP 2009). Most of this exposure results from elevated radon in homes, and there is a small increased risk from long term exposure to elevated radon concentrations, especially in smokers. Refraining from smoking and testing your home from radon are the best ways to reduce this baseline risk.

We hope that this helps put your mind at ease regarding your work experience with radon'

 

[Paultx]

I just did the worst case scenario calculations (which is impossible to happen since most of the canisters were used in homes and not in underground caves), which would be to assume that in the place where the 200 canisters were located there were 1000 Bq/m³ = 1KBq/m³
If we take into account the results of the following experiment:
https://pmc.ncbi.nlm.nih.gov/articles/PMC8122700/
on the adsorption of radon in activated charcoal, we know that the amount of radon adsorbed in the activated charcoal is:
1.41 ± 0.21 Bq/g per kBq/m³
That is, for each KBq/m³ of activity in the place where the canisters were located, the activated charcoal has adsorbed 1.41 Bq/g.

Each of the canisters contained 75 g of activated charcoal. If we multiply 75 by 200 canisters, we have a total mass of 15000 g of activated charcoal.
Since the radon activity adsorbed by activated charcoal is 1.41 Bq/g, and we have 15000 g of activated charcoal, we will have a total activity of 1.41 multiplied by 15000 = 21150 Bq
Since 1 Ci = 3.7 10exp10 Bq, we will have an initial total activity of 571621 pCi.

Now, we are going to take into account the calculations of gleem, who is an RSO, who posted the following: ‘What is the Radon level in your house? Even if it is very low, for example, 0.1 pCi/L (the U.S. average is 1.3 pCi/L), living in it 16 hours a day, seven days a week for 13 years, you will inhale at a rate of 6L of air per minute (average adult) 2,725,632 pCi’.

Then, we realize that in the worst possible case, the initial canister activity was a total of 571,621 pCi, which is a much lower number than the 2,725,632 pCi that a person would be exposed to in their home with a level of 0.1 pCi/L over 13 years.

But since the normal activity in a home is 1.3 pCi/L (and not 0.1 pCi/L) the activity that a person would be exposed to over 13 years in his own home would be 35433216 pCi.

Conclusion:
- In the worst case scenario, I would have been exposed to an activity of 571,621 pCi
- A person living in an average home in the United States is exposed, over 13 years, to an activity of 35,433,216 pCi. This activity is 62 times higher than the activity to which I was, in the worst case scenario, exposed.
After having done these calculations, we clearly see that the danger to which I was exposed is almost 0.