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rfisher
03-14-2011, 03:32 PM
There's been a lot of concern about the events taking place in Japan with the nuclear reactors. The media is really mixed in it's reporting, but much of it is designed to be sensational rather than educational or factual. I am a medical imaging program director with all sort of initials behind my name that don't mean a lot to any of you. I teach radiobiology and radiation physics. I'm responsible for ensuring 50 students a year understand radiation safety for themselves, their patients and the general public. All that is to provide professional background. Most people are afraid of radiation, yet most really don't have any understanding of what it means. Just this week one of my students had a patient get very upset when she left her glasses in the room after a chest x-ray. She was convinced they were now radioactive. So, I'm going to post some basic information about radiation dose and what that means from a biologic perspective. Feel free to post questions and I'll try and answer. I will leave answers regarding the physical aspects of the nuclear plant to a couple of poster who actually work at such facilities, but feel free to post those questions as well.

1. All ionizing radiation has the potential to cause biological harm. That includes UV and infrared light, x-ray, particulate radiation and gamma rays (what's coming from the reactors). Potential is the key. The probability of any harm actually occurring is dependent on how much radiation (dose) is received, to what body part (whole body vs. selected organs), and the quality of the radiation. I could take a piece of Polonium-218 and put it on my desk, cover it with a piece of paper, and receive no radiation. However, if I swallowed that piece of Polonium, I'd probably die because of the severe damage to my GI tract. This is what killed the Russian spy several years ago. That's because the radiation produced by Polonium has a very high rate of transferring it's energy to tissue, but it does it within a couple of millimeters. Gamma radiation, OTOH, has a relatively low rate of energy transfer, but it has a significant range (distance) in which to do so.
2. How far can it travel? It depends. The gamma ray will interact with the air in which it is traveling. It ionizes or causes an electron to be removed from atoms it encounters. The greater the distance it travels, the less energy it has when it encounters something else. It's the transfer of energy along with the removal of an electron that can cause biological harm. So, the farther away you are, the less exposure you will receive. In fact, we call the Cardinal Principles of Radiation Safety : Time, Distance, and Shielding. Minimize the time of exposure, maximize the distance and shielding. Shielding is putting something between you and the radiation.
3. What does it mean when they say levels are 8 x normal? I think everybody knows what 8 x means, so the real question is, is that bad? What's normal?
The other basic principal of radiation safety is called ALARA which stands for As Low As Reasonably Achievable. This is the underlying principal for medical radiography as well as industrial radiation production. We want to keep any dose level as low as possible. Minimum dose levels are set by the International Commission on Radiation Protection (http://www.icrp.org/) and the National Commission on Radiation Protection (US). They base these lower than what research has taught us, sadly much from the Hiroshima and Nagasaki data along with other populations, are the dose thresholds for different biological effects.
4. These minimum levels take into consideration radiation from multiple sources: cosmic, cosmogenic (within the Earth's atmosphere), terrestrial (radon is a prime example), naturally occurring radioisotopes etc. I'll give some sample amounts below. The real key here is that the dose limits are set well below levels of known biological effects. It is undeniable that even a very low dose, one photon, could cause a biological effect, but the statistical odds are really small. My students are always a little annoyed after I've presented all the things that could happen when they do a single chest x-ray when I conclude with the greater probability that they won't. It's always a weighing of risk vs. benefit.
5. Some example radiation doses: if you live in France, you receive approximately 0.00071 Sieverts annually, but if you live in Austria you only get 0.00037. If you smoke you get about 0.08 Sievert to your lungs. Dose limits vary but the goal is to keep public exposure below 1milliSv/year for a total body exposure (individual organs and the lens of the eye are somewhat higher). That's less then what your lungs are getting all ye smokers. This would be based on medical x-ray exposure or anything above the natural background exposures. The exposure coming out of the plant was approximately 70 microSv on the last report I saw. Meaning somebody exposed would be well below the accepted minimum annual limit. We would not expect them to have any biological ramifications.

I don't use Wikipedia for references, but I'll be happy to supply a list of technical journal or book references if anybody so desires. I know how some want their links. :)

MichaelK
03-14-2011, 03:50 PM
I agree with your assessment that somewhat higher than 'normal' dosages of radioactivity in a not too long time frame are unlikely to be harmful. However, in Japan it is not clear how much radioactive material escaped from the reactor and reports are conflicting in that regard. It is hard to imagine after what happened that the radioactivity in the reactor was fully contained. Fortunately the wind is blowing the stuff off to the sea for now. But I can also understand worries that the situation is more serious as is admitted by officials and a larger amount of radioactivity got released.

rfisher
03-14-2011, 04:02 PM
The dose of the radiation released is very small. What would be a problem is if there was a significant quantity or someone remained in that quantity a long time which would increase their total exposure. The dose picked up by the US pilots was much less than the the normal background radiation exposure. That someone receives everyday. Now, it's prudent to remove people from receiving additional exposure (anything above background levels), but it's unlikely that anybody has received a significant dose that will cause either immediate or long term health issues. When we do a CT scan on a patient they are getting a significant increase in exposure above their background levels, yet we perform this exam everyday without doing harm. That could change if there was a massive release of radiation, but everything in the media indicates that is not the situation. Some radioactivity was present in the two explosions, yes. However, the dose would be very small.

One thing very different in all nuclear reactors now (after Chernobyl) is that the radioactive material is contained within a separate steel container apart from the concrete containment tower that exploded due to the build up of hydrogen gas. It is a matter of keeping sufficient cooling on the rods until they cool on their own.

MarieM
03-14-2011, 04:08 PM
Just to add one thing about the ICRP (I prefer the french CIPR bah) is that you can find tons of useful information on their site. Like the annual dose received in your area and so on.

Actually, all the recommandations of the ICRP are taken into account at the European level, like with EURATOM 96-29 and so forth. I know for sure it's the same in Japan.

rfisher : the lastest news coming from the french safety agency is that the amount released during the explosion of number 1 reactor was approximatively 1 mSv/h for 3 hours, then it decreased and is now less than 50 ÁSv/h next to the reactor facility. They are running calculations (MONTE CARLO based) to assess the amount probably rejected in the environnement.
They are not sure however their data is accurate. They think a large amount, more than reported, has been released in the atmosphere, but wasn't on the scale of what is reported in certain press agencies. They tend to believe thanks to weather broadcast that it all went to the pacific side and not too much inland. They also state that measures are taking place at the moment in the 20 kms evacuated to evaluate the impact of the blasts.

Just one other fact, safety agencies have got a tendency to report facts in a very negative and conservative point of view : they were created to be like that and that's very very good in those circumstances.

dbny
03-14-2011, 04:21 PM
Thanks for posting some clarifications re radiation.


When we do a CT scan on a patient they are getting a significant increase in exposure above their background levels, yet we perform this exam everyday without doing harm.

We actually do not know for a fact that no harm is done. There must be a certain number of people (be it ever so small) for whom just one CT scan happens to cause damage that results in cancer. The benefits of CT scans, in general, outweigh the risks, but fewer are better, and none is the best. Ironically, cancer patients are often given multiple CT scans over relatively short periods of time. Choose your poison.

rfisher
03-14-2011, 04:40 PM
Thanks for posting some clarifications re radiation.



We actually do not know for a fact that no harm is done. There must be a certain number of people (be it ever so small) for whom just one CT scan happens to cause damage that results in cancer. The benefits of CT scans, in general, outweigh the risks, but fewer are better, and none is the best. Ironically, cancer patients are often given multiple CT scans over relatively short periods of time. Choose your poison.

As I said, and as I teach my students, you do damage with every exposure. You do damage every time you expose your skin to the sun. UV radiation can cause skin cancer. However, there are a number of factors that determine if radiation damage is significant. What cell is hit, where it's hit, how often it's hit, whether a critical target structure is hit and so on. Most of the time a water molecule is hit and the molecule immediately reforms leaving no damage. DNA has a remarkable repair mechanism. We teach that there is no minimum dose but acknowledge the reality most all cancers have a threshold that must be crossed. That threshold dose varies considerably.

made_in_canada
03-14-2011, 04:55 PM
Thanks for sharing your expertise, rfisher.

agalisgv
03-14-2011, 06:28 PM
the goal is to keep public exposure below 1milliSv/year for a total body exposure (individual organs and the lens of the eye are somewhat higher).
the lastest news coming from the french safety agency is that the amount released during the explosion of number 1 reactor was approximatively 1 mSv/h for 3 hours Since I don't know this area at all, I just wanted to ask a clarifying question--does MarieM's post mean that for three hours, people in the vicinity of the nuclear reactor were exposed to a year's worth of radiation exposure?

If that's true, what would be the potential biological ramifications of that?

Thanks for taking the time to respond :)

rfisher
03-14-2011, 06:43 PM
It really depends. One would have to be standing in the reactor to receive that rate. Distance of even a meter reduces the dose by 1000. It's inversely proportional to the square of the distance. Meaning the further away you are, the less dose by a factor of 4. That minimum annual dose is exceeded by many people. Airline pilots, for example, or even people who live at high altitudes. It's an average recommended level. Biological consequences vary but the risk for developing leukemia, for example, is .1% after an exposure of .1 SV which would take almost 1000 hours of exposure at that rate, and then the risk is less than 1%. They have evacuated people living close to the facility. Even if it were to have a catastrophic radiation leak, the people who would be most impacted are the workers at the plant.

Sylvia
03-14-2011, 07:17 PM
Does this Reuters article contain accurate information? Japan nuclear disaster risk seen receding fast (http://www.reuters.com/article/2011/03/14/us-japan-nuclear-radiation-risk-idUSTRE72D6UC20110314)

What about this BBC News video report? What is happening in quake-stricken Japan nuclear plant? (http://www.bbc.co.uk/news/world-asia-pacific-12739184)

ETA: BBC News' Q&A re. Japan's nuclear alert at Fukushima (http://www.bbc.co.uk/news/world-asia-pacific-12732015)

rfisher
03-14-2011, 07:39 PM
Does this Reuters article contain accurate information? Japan nuclear disaster risk seen receding fast (http://www.reuters.com/article/2011/03/14/us-japan-nuclear-radiation-risk-idUSTRE72D6UC20110314)

What about this BBC News video report? ]What is happening in quake-stricken Japan nuclear plant? (http://www.bbc.co.uk/news/world-asia-pacific-12739184)

It would seem so. They will have a significant issue with clean up. It won't pose a health issue to the general population, but it's going to be extremely expensive and they will have a problem disposing of the material. The cost is going to be in the billions both in loss of generating capacity and in clean up. I have to assume the Japanese environmental protection people will do whatever it takes to minimize the environmental impact. I just hope they don't opt for the dump it at sea option.

Disposal of radioactive waste is my biggest issue with nuclear power. The US has had an ongoing battle with disposing of tons of material at the Yucca Mountain facility for years. It's been blocked in the courts several times :cheer2: but is up for discussion again. :(

jsh5
03-14-2011, 07:48 PM
I'm a chemist by training as well, so this has me curious about areas I don't know much about. I know that one treatment for exposure is flooding the thyroid with iodine - is the body particularly sensitive to iodine or is it just that it persists in certain organs and causes damage longer?

Wiery
03-14-2011, 08:02 PM
Thank you very much-very helpful and thoughtful post, rfisher!

MarieM
03-14-2011, 08:11 PM
Does this Reuters article contain accurate information? Japan nuclear disaster risk seen receding fast (http://www.reuters.com/article/2011/03/14/us-japan-nuclear-radiation-risk-idUSTRE72D6UC20110314)

What about this BBC News video report? What is happening in quake-stricken Japan nuclear plant? (http://www.bbc.co.uk/news/world-asia-pacific-12739184)

ETA: BBC News' Q&A re. Japan's nuclear alert at Fukushima (http://www.bbc.co.uk/news/world-asia-pacific-12732015)

Great articles, well documented with facts and accurate data ! There is hope after all ! :)

MichaelK
03-14-2011, 08:13 PM
I'm a chemist by training as well, so this has me curious about areas I don't know much about. I know that one treatment for exposure is flooding the thyroid with iodine - is the body particularly sensitive to iodine or is it just that it persists in certain organs and causes damage longer?

The thyroid needs iodine for producing thyroid hormones, therefore iodine is preferably stored in the thyroid. This means that radioactive iodine will be stored as well in the thyroid where it may lead to cancer. In fact thyroid cancer is known to be much more prevalent in the Chernobyl area after the disaster - so it is a real danger.

If people take iodine pills the thyroid is saturated with iodine and no more potentially radioactive iodine will be stored and the risk of cancer will be greatly reduced by taking the pills.