Is that a Banana in Your Pocket or Are You Radioactive?

March 18, 2011

Ronald Wayne says:

Many people and the media (esp in the USA) need to calm down. Anyway, did you forget other elements to daily radioactive isotope soup such as C-14 the chemical backbone of organic life (yeah very small exposure though), and less trivial, radon in our basement, cosmic rays etc.  People need to come to a realization that instead of developing an irrational fear of man-made nuclear emissions (while forgetting other sources) and demanding the the suppression of nuclear developments would be a backward step for our civilization. We need to conquer it just as we conquered fire, electricity and other inherently "dangerous" things. Indeed it poses unique and more intractable challenges than we have overcome before (so don't go pointing out how electicity is not as bad as nuclear!) but such is nature of the learning curve on the road of technical advancement-the challenges not only recur but they become increasing difficult! Instead of scrapping nuclear energy developments we should probably put more money into researching the inorganic chemistry and nuclear physics of these radioactive isotopes to accelerate the development of practical and reliable separation and transmutation techniques to neutralize radioactive waste, then one day our decendends would probably walk around with nuclear powered devices (exploiting the high density of nuclear energy) including nuclear powered artificial hearts etc. Cheers!

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March 18, 2011

A guest says:

The OP and the first comment contain a mixture of good info and falsehoods. Yes, the planet is radioactive, as is the cosmos, our bodies, and our food. Yes, coal includes uranium and other radionuclides, and some of that radioactivity is emitted along with the (enormous) exhaust gases. And yes, many people are irrationally over-concerned about radiation, while others are irrationally blase about this hazard and others.

The two most important falsehoods are the ones that contradict the following two facts:

1) Coal burning actually DEcreases our exposure to radiation! and

2) Eating one or many bananas increases your radiation exposure by ZERO. The "banana equivalent dose" is completely wrong, based on accurately multiplying the WRONG numbers together. Garbage in, garbage out.

First the coal: Yes, there's radioactive stuff in the coal and the emissions (less from "cleaner coal" stations), and it increases our doses through inhalation and ingestion. BUT the biggest fraction of the emissions from a coal-burning station BY FAR is CO2. And because the coal is prehistorically ancient -- way older than 20 half-lives of Carbon-14, a very common radionuclide in nature, our built environment, and our BODIES, this CO2 contains only pure non-radioactive Carbon-12. It DEcreases our total radiation dose by diluting that C-14 in the air, and the entire environment, including our food and us. That decrease dwarfs the increase from the uranium (etc.) in the coal. Strange but true!

Now the bananas (and milk, and other potassium-rich foods): Basically, the guy at the US nuclear lab (my computer remembers his name and the lab's name -- me, not so much) who first calculated this dose, applied the dose coefficient for K-40 to the K-40 content of an average banana, as explained in the quote above. It sounds reasonable, but it's wrong. If you ingested that radioactive Potassium without the stable potassium that it's mixed with, you would actually receive that dose. But that's not what's in the banana. Our bodies contain the same mixture of radioactive and stable (non-rad) K (Potassium) as the banana does. Most of us also pretty well nourished, so we contain the amount of K our bodies require, but that's partly another point.

Eat a 400-gram banana, and your store of potassium -- radioactive and stable -- becomes a bit bigger. But you simultaneously become 400 grams bigger, too. The radioactive portion of your body's potassium -- it's called "terrestrial equilibrium" because it's the same throughout the earth's ecosystems -- is unchanged. And your dose -- measured in mSv or mRem, all of which measure dose per unit of body mass exposed -- doesn't change, either. In addition, our bodies maintain our total body burden of potassium (unless we're malnourished), so our total amount of K40 doesn't change with the banana-intensity of our diet, either.

Looking back and squinting, the two facts -- about carbon and potassium -- are quite similar: Our bodies contain a relatively fixed quantity of both of those elements, so what determines our radiation dose from them is the FRACTION of our internal C and K that is radioactive, not how much we eat. Consuming C that is unusually non-radioactive (less radioactive than the equilibrium in the surface ecosystem) decreases our dose. Consuming K that is IDENTICALLY radioactive as all the other K, has no impact.

BTW, the reason that radioactive pollution -- radioactive iodine, Cs-137, uranium -- increases our radiation dose by ingestion and inhalation is a combination of two factors:

1) As in the case of the Iodine, the emissions are more radioactive than the Iodine we're normally exposed to, and that we've incorporated into our bodies (thyroid glands). So that increases the radioactive FRACTION of our Iodine. Similarly, flooding our thyroids with stable Iodine (with KI pills), ensures that we won't take up any of the bad Iodine.

2) As in the case of the Cs-137 and the U (at terrestrial equilibrium in the coal), these elements are rare in our food and our bodies, but they "mimic" common elements that share their chemical behavior (valence). As I recall, Cesium is a Phosphorus mimic, so this radioactive Cs-137 will replace some much less radioactive Phosphorus in our tissues. I forget offhand what Uranium mimics, but the effect is the similar.

Putting ANY of this "into perspective" by comparing it to eating bananas is Just Plain Wrong.

BTW, I've posted this correction on a list-serv that included the original perpetrator of the confusion and a number of his colleagues. So at this point, even if the original error was an honest mistake, I think we're into the realm of intentionally spreading falsehoods that help win an argument (that should be lost, IMHO).

Of course, many normal people are shocked and disequilibrated just to find out that their bodies and their food includes radionuclides, and the new info may make them happier to live downwind from a reactor or six. And the lie is simpler than the truth, too. . .

Norm Rubin, Director of Nuclear Research, Energy Probe, Toronto (Canada)

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March 18, 2011

A guest says:

I know you are attempting to enlighten us and possibly calm us down, but I am not feeling the humor in your ending quip. I guess I am just too devastated over this development to see the funny.

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March 17, 2011

David Lewis says:

Radiation isn't just coming at you from bananas.  The Earth is radioactive.  Radiation also enters the planetary system from space.  Life evolved on an even more radioactive planet.  Earth's radioactivity is slowly declining.  But nevertheless, these days, measurements show that an average American's exposure is dramatically increasing.   

This non news comes from the National Council on Radiation Protection (the NCRP), an organization chartered by Congress in 1964 to collect and disseminate information and recommendations about radiation in the public interest.  

The average yearly dose for an American in the 1980s was 360 millirem/yr

The green part of the pie is "normal" background radiation, the radon emanating from your basement, the cosmic rays coming into the system from space, etc.  The yellow slice is what medical imaging amounted to back then.  The entire rest of what an average person gets from consumer products and occupational exposure is the dark purple.  The nuclear industry's total effect on your life could be cut out of this chart and it would not show up.  

By 2009 this picture has changed dramatically.  The entire pie is larger because the average dose level has increased 58% or by 260 mrem.  

Note also the relationship between slices.  Now Medical imaging contributes almost 300 mrem, which is getting close to the entire "normal" dose an average American received a few decades ago.  That 1980s "normal" is about what human beings have been receiving since apes first came out of the trees.  Medical imaging exposure is increasing so rapidly this 2009 chart is already obsolete:  the NCRP has announced since it published this that for the first time, medical imaging amounts to more than 50% of average total exposure.  

Another way to look at this:  early human beings in preindustrial civilization were exposed to a certain amount of radiation.  Now we've doubled it.  

The NCRP notes that some studies show that as much as 100 mrem of this medical imaging increase comes because of "defensive" medicine, i.e. because doctors are afraid of getting sued by their patients, which causes them to order unnecessary tests.  

We're glowing in the dark because our doctors are afraid of getting sued by our lawyers, but the big public issues on the radiation front for decades are connected with the nuclear power industry.  

Coal plants emit more radiation than nuclear plants but get a free pass on this.  Coal contains uranium and thorium which survive burning, become part of the ash, and are emitted right out the stack.  

The big new US gas discoveries are taking place in shales once classed as uranium ore.  They are so radioactive that the resulting in gas is much more radioactive than previous gas, which already exposed users of it to an order of magnitude greater radiation dose than living next door to a nuke plant, but again, it can't be pinned on the nuke industry, so it gets a free pass.  

On the other hand:  Public ignorance and uber-concern about radiation has led public officials to cater to radiation standards that are unevenly applied - the nuclear industry couldn't convince the public to accept a plan to bury nuke waste in a place very near where almost 1000 nuclear bombs had already been exploded, in part because of public concern that someone wandering around the surface of the proposed area thousands of years from now might get an increased exposure of 15 extra mrem 10,000 years from now.  We've added almost 100 mrem to our exposure because we are trigger happy when it comes to suing our doctors.  That's all of us who live here on average, not just the ones who would wander around at the surface near Yucca 10,000 years from now.  

Politics doesn't have to make sense - if the public demands, the politicians will serve it up.  But we don't have to pretend it makes sense.  Arguing that this radiation policy is ridiculous is deemed to be a sign that you are one of the pro nuclear special interest types always looking for a way to flog your favorite power source.  

Fear of radiation exposure is what is driving the hysteria in coverage of Fukushima today.  A year from now the zealots will be telling Japanese how many of them will be killed because their average exposure went up a few mrem.  This is insane, and it has been playing out for years.  The planet is being killed because we're pretending we don't have a low carbon power source.  

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