Radiation Safety: Understanding Exposure and Risk

[spark90]

Good day.

As a Radiation Protection Specialist, with 30 years of experience, I can assure you that the risk to you, from fiddling with the Americium-241 source inside your smoke detector, is negligible. The quantity of radioactivty in such a detector is, in regulatory jargon, Exempt from being regulated. This means that the radiation dose, which anyone can be exposed to, by fiddling with the source, is considered too small to cause any harm. Yes, this does come from very detailed risk assessments which have considered ALL potential scenarios of "playing with the source" and the resultant radiation dose. Wherever you are living, if it was considered that the smoke detector could be harmful it would never have been sold to you as a member of the general public. I hope this puts your mind at ease. Of course, there's no harm in washing your hands after touching the source which I am sure that you did. If you didn't the potential radiation dose would still be negligible.

Paul

That is very good of you to reply thank you so much. As you are an expert could you explain a post I saw on another forum which stated " It is the alpha recoil reaction that can destroy the thin coating over the source and allow source material to recoil out of the source." Apparently this caused a yellow discharge from someone's ionisation chamber which collected as a dust around the ionisation chamber, although the activity was 5 microcuries. " Could this occur in my smoke detector which is 27 years old and 0.9 microcuries. I was concerned as dust fell in my eye when I opened the detector and was worried when I read that the thin metal seal on the source can breakdown due to alpha particles over time and hence release the decay products and was worried this had came out of the ionisation chamber due to the age of my smoke detector. Thanks again

 

[Phinrich]

Off the top of my head, I would answer as follows.

Firstly, I am not encouraging you to eat the Americium 241 source, but when I say that the exemption of the source (based on a level of 5 mico-curies activity), is based upon assessing all possible ways for you to be exposed to it, that would include you eating the source. That's shocking to say and I am by no means suggesting that anyone should do this. Still, someone has done a calculation to determine what radiation dose would be received by such a foolish act and they have determined it to be negligible. In such a scenario the source would most likely be expelled from the body along the digestive tract and pass harmlessly out.

Speaking about the "disintegration of the source", if we ignore any "break-up" of the source (recoil and all that), what it means to say that the source is radioactive means that every second it shoots out, in this case, alpha particles (helium nuclei) and thereby leaves behind less radioactivity. A 5 micro-Curie source will emit 200 000 alpha particles every second (to begin with). Do not be frightened by this large number as most of these alpha particles will get stopped by air molecules immediately around the source without exiting the chamber of the detector (assuming no holes in the chamber outer wall). Even if there is a hole or two in the chamber walls alpha particles do not carry a lot of energy and again will collide with millions of air molecules as they travel and will very soon lose all their energy. Americium-241 has a half-life of 432 years. What this means is, if we could count the number of alpha particles emitted per second, today, and get 200 000, then 432 years later, if we measured, we would get 100 000 alphas per second (half of the original amount). After another 432 years, we would get 50 000 and so on. I agree that there may be mechanisms for the casing of the detector to break-down. The question of the possibility of alpha-recoil I see as a pure physics question which I will leave to the physicists to answer. The point is, should there be breaks in the outer casing of the detector which allow the escape of source material (speaking here about small fragments of the source rather than emitted alpha particles as we have said that alpha particles do not travel very far in the air). If small fragments of the source material do escape (by breaking off the source due to age) and even if those fragments got into your eye, these fragments (dust) would continue to emit alpha particles in your eye. However, these alpha particles would not get deeper than the first tissue layer of the eye before being stopped. It is not the alpha particle that causes tissue damage leading to radiation damage, it is the ënergy carried by a moving alpha particle. A moving alpha particle may be thought of as a small moving bullet. However, the bullet very soon loses energy and stops moving. A bullet that is not moving cannot do any damage. Once the moving alpha particle has lost its energy, by colliding with the more dense tissue in the first layer of tissue of the eye, they lose their ability to cause any radiation damage to the eye or to any other part of the body. The "dead" alpha particles will then most likely be washed out of your eye by natural tears or be absorbed into your tissue harmlessly. So yes we are surrounded by natural radiation, and as a member of the public, you may be exposed to many different sources of radiation. For example, exposure to your smoke detector or a visit to the doctor resulting in an X-ray image being taken. According to international standards, as a member of the public, you are allowed a total radiation dose of 1 millie Sievert per year, from all sources, without it being considered harmful to you. As a Radiation Protection Specialist, I work with radioactivity almost daily. I wear a radiation monitor which records my daily dose. I am allowed a total of 20 milli Sieverts per year (20 x your dose) without it ever being considered harmful to me. In my 30 years of doing this job I have never ever gotten anywhere near to 20 millie Sieverts radiation dose in a single year.

I hope this is helpful and please feel free to ask more questions.

Paul

 

[Phinrich]

Speaking of having radioactive material inside your eye, in an earlier job I worked as a medical physicist at a large hospital with a radiotherapy Unit. There is a rare condition known as Retinoblastoma which leads to a cancer tumour inside the patient's eyeball. We would treat this condition (very successfully) by purposefully placing radioactive Iodine-125 sources inside the patient's eye socket to give radiation to the tumour. The geometric arrangement of the sources was very carefully calculated on a computer and we used more than 5 micro Sieverts of activity for each such procedure. After a calculated number of days, the sources were removed and the tumour was successfully treated and the patient's eyesight was saved.

Paul

 

[spark90]

Speaking of having radioactive material inside your eye, in an earlier job I worked as a medical physicist at a large hospital with a radiotherapy Unit. There is a rare condition known as Retinoblastoma which leads to a cancer tumour inside the patient's eyeball. We would treat this condition (very successfully) by purposefully placing radioactive Iodine-125 sources inside the patient's eye socket to give radiation to the tumour. The geometric arrangement of the sources was very carefully calculated on a computer and we used more than 5 micro Sieverts of activity for each such procedure. After a calculated number of days, the sources were removed and the tumour was successfully treated and the patient's eyesight was saved.

Paul

Thank you for your replies. Those are very detailed answers you gave me. I was only asking because I had read online of a 1970's smoke detector which had leaked a yellow dust which was covering the ionisation chamber and the physicist replied that it was due to the alpha recoil breaking down the seal over the americium that meant that the decay product of Np could escape and this was the yellow dust and hence I read it is very dangerous to inhale such things and I obviously would have inhaled falling dust!

 

[Phinrich]

Hope the answers were not too detailed. I was trying to put your mind at ease. I agree with the Physicist regarding where the yellow dust could have come from and also I agree that it is "dangerous" in the sense that, although the quantity of radioactivity is small, it's a good policy to keep away from it if you can.

 

[spark90]

Hope the answers were not too detailed. I was trying to put your mind at ease. I agree with the Physicist regarding where the yellow dust could have come from and also I agree that it is "dangerous" in the sense that, although the quantity of radioactivity is small, it's a good policy to keep away from it if you can.

So you think that the yellow dust on the inner cover of my smoke detector was emitted through the ionisation chamber by the decay of the americium?

 

[Phinrich]

I am afraid I have very little experience with Americium smoke detectors. Although I work for my countries nuclear regulator the regulation of smoke detectors is handled by another regulator. I have spoken to you about the principles and practice of radiation protection, in general. My point was that if your government allows these devices into your home then it is because they are known to be safe. Without knowing the composition of the dust I cannot say where it came from. I have no experience to confirm that the Americium source could break-up as it ages physically. I guess it could. And maybe it does lead to a powder on the outside of the detector. Having no experience I would not want to confirm it positively. I suggest you possibly talk to the supplier. Or perhaps someone with the right experience could join the conversation. If Americium sources can break-up and lead to powders which you could ingest, and if this ingestion was dangerous your government would not allow you to have them inside your house.

 

[spark90]

I am afraid I have very little experience with Americium smoke detectors. Although I work for my countries nuclear regulator the regulation of smoke detectors is handled by another regulator. I have spoken to you about the principles and practice of radiation protection, in general. My point was that if your government allows these devices into your home then it is because they are known to be safe. Without knowing the composition of the dust I cannot say where it came from. I have no experience to confirm that the Americium source could break-up as it ages physically. I guess it could. And maybe it does lead to a powder on the outside of the detector. Having no experience I would not want to confirm it positively. I suggest you possibly talk to the supplier. Or perhaps someone with the right experience could join the conversation. If Americium sources can break-up and lead to powders which you could ingest, and if this ingestion was dangerous your government would not allow you to have them inside your house.

Thank you, you have been really generous with your time. Very grateful!

 

[Phinrich]

It's a pleasure. It is 22:30 here and I am retiring for the night. If you ask more questions I will answer them tomorrow. Have a GREAT day.

 

[Phinrich]

The following link may be of interest to you;

https://valueguardinspections.com/h...etectors are an,and likely should be replaced.

It states that old smoke detectors often turn yellow because smoke detector manufacturers often inject a fire retardant bromine into the plastic of residential smoke detectors. Bromine serves a dual purpose. It helps protect the unit in the event of a fire and also serves as a visual signal the detector is older and likely should be replaced.

 

[cmb]

On the matter of 'have I increased my risk of cancer', I seem to recall seeing other threads along similar lines recently.

The answer to 'that' side of the question is that a little exposure to ionising radiation appears to be good for humans. They have evolved to live and thrive on a planet showered with high energy cosmic radiation, and apparently there is some response from the cell genetics to 'a little' radiation that is not simply unharmful but positively beneficial.

The assumption that 'any' radiation is bad for you is a cautionary one as it is better to assume that 'nothing' of something bad is optimum if one has no idea of the detail, which was the case in the early days.

It's pretty clear now that exposure to radiation is bimodal and does not follow a straight line path of cancer-causality for small dose cases (as would be the case here) in the order of background levels.

Rates of cancer in the world are generally inversely related to the natural background radiation.

Radiation is a hidden bogey-may/invisible monster and therefore invokes fear. This is understandable. But trust the science and engineering. A smoke detector is designed to package away harmful radioactive materials from commonly prying hands.

 

[Phinrich]

Thank you for your comment. You are ABSOLUTELY correct. We are exposed to little bits of radiation every day and the species has been exposed for millennia and it is certainly possible that a little radiation is good for us and may in fact help with the evolution of the species. I didn't want to get into all of that yesterday but I do agree with you. Thank you for adding that.

 

[Keith_McClary]

a little radiation is good for us and may in fact help with the evolution of the species

The same has been said of extinction events.

 

[Phinrich]

TRUE! That's a GOOD one. I'd rather take my chances with a little radiation than with a little extinction THANK YOU! At least until Mr. Musk gets us colonizing Mars.

 

[nickelcadmiumbattery]

Off the top of my head, I would answer as follows.

Firstly, I am not encouraging you to eat the Americium 241 source, but when I say that the exemption of the source (based on a level of 5 mico-curies activity), is based upon assessing all possible ways for you to be exposed to it, that would include you eating the source. That's shocking to say and I am by no means suggesting that anyone should do this. Still, someone has done a calculation to determine what radiation dose would be received by such a foolish act and they have determined it to be negligible. In such a scenario the source would most likely be expelled from the body along the digestive tract and pass harmlessly out.

Speaking about the "disintegration of the source", if we ignore any "break-up" of the source (recoil and all that), what it means to say that the source is radioactive means that every second it shoots out, in this case, alpha particles (helium nuclei) and thereby leaves behind less radioactivity. A 5 micro-Curie source will emit 200 000 alpha particles every second (to begin with). Do not be frightened by this large number as most of these alpha particles will get stopped by air molecules immediately around the source without exiting the chamber of the detector (assuming no holes in the chamber outer wall). Even if there is a hole or two in the chamber walls alpha particles do not carry a lot of energy and again will collide with millions of air molecules as they travel and will very soon lose all their energy. Americium-241 has a half-life of 432 years. What this means is, if we could count the number of alpha particles emitted per second, today, and get 200 000, then 432 years later, if we measured, we would get 100 000 alphas per second (half of the original amount). After another 432 years, we would get 50 000 and so on. I agree that there may be mechanisms for the casing of the detector to break-down. The question of the possibility of alpha-recoil I see as a pure physics question which I will leave to the physicists to answer. The point is, should there be breaks in the outer casing of the detector which allow the escape of source material (speaking here about small fragments of the source rather than emitted alpha particles as we have said that alpha particles do not travel very far in the air). If small fragments of the source material do escape (by breaking off the source due to age) and even if those fragments got into your eye, these fragments (dust) would continue to emit alpha particles in your eye. However, these alpha particles would not get deeper than the first tissue layer of the eye before being stopped. It is not the alpha particle that causes tissue damage leading to radiation damage, it is the ënergy carried by a moving alpha particle. A moving alpha particle may be thought of as a small moving bullet. However, the bullet very soon loses energy and stops moving. A bullet that is not moving cannot do any damage. Once the moving alpha particle has lost its energy, by colliding with the more dense tissue in the first layer of tissue of the eye, they lose their ability to cause any radiation damage to the eye or to any other part of the body. The "dead" alpha particles will then most likely be washed out of your eye by natural tears or be absorbed into your tissue harmlessly. So yes we are surrounded by natural radiation, and as a member of the public, you may be exposed to many different sources of radiation. For example, exposure to your smoke detector or a visit to the doctor resulting in an X-ray image being taken. According to international standards, as a member of the public, you are allowed a total radiation dose of 1 millie Sievert per year, from all sources, without it being considered harmful to you. As a Radiation Protection Specialist, I work with radioactivity almost daily. I wear a radiation monitor which records my daily dose. I am allowed a total of 20 milli Sieverts per year (20 x your dose) without it ever being considered harmful to me. In my 30 years of doing this job I have never ever gotten anywhere near to 20 millie Sieverts radiation dose in a single year.

I hope this is helpful and please feel free to ask more questions.

Paul

You are the absolute god of explanations. Your narrative was like ASMR for the intellect.