While doing some research on Thorium, I came across this interesting little fact that I wasn’t familiar with, so I thought I’d pass it along. Many people fear radiation, sometimes the fear is irrational, based on the erroneous concept that we live in a “radiation free lifestyle”. I’ll never forget one time when I showed my geiger counter to a neighbor who was shocked when it started clicking. She was horrified to learn that cosmic rays were in fact zipping right through her body right that very second. I didn’t have the heart to tell her about neutrinos.
But, along the same lines, this little factoid might drive some people “bananas” when they read it. But, it illustrates a fact of life: radiation is everywhere.
A banana equivalent dose is a concept occasionally used by nuclear power proponents[1][2] to place in scale the dangers of radiation by comparing exposures to the radiation generated by a common banana.
Many foods are naturally radioactive, and bananas are particularly so, due to the radioactive potassium-40 they contain. The banana equivalent dose is the radiation exposure received by eating a single banana. Radiation leaks from nuclear plants are often measured in extraordinarily small units (the picocurie, a millionth of a millionth of a curie, is typical). By comparing the exposure from these events to a banana equivalent dose, a more intuitive assessment of the actual risk can sometimes be obtained.
The average radiologic profile of bananas is 3520 picocuries per kg, or roughly 520 picocuries per 150g banana.[3] The equivalent dose for 365 bananas (one per day for a year) is 3.6 millirems (36 μSv).
Bananas are radioactive enough to regularly cause false alarms on radiation sensors used to detect possible illegal smuggling of nuclear material at US ports.[4]
Another way to consider the concept is by comparing the risk from radiation-induced cancer to that from cancer from other sources. For instance, a radiation exposure of 10 mrems (10,000,000,000 picorems) increases your risk of death by about one in one million—the same risk as eating 40 tablespoons of peanut butter, or of smoking 1.4 cigarettes.[5]
After the Three Mile Island nuclear accident, the NRC detected radioactive iodine in local milk at levels of 20 picocuries/liter,[6] a dose much less than one would receive from ingesting a single banana. Thus a 12 fl oz glass of the slightly radioactive milk would have about 1/75th BED (banana equivalent dose).
Nearly all foods are slightly radioactive. All food sources combined expose a person to around 40 millirems per year on average, or more than 10% of the total dose from all natural and man-made sources.[7]
Some other foods that have above-average levels are potatoes, kidney beans, nuts, and sunflower seeds.[8] Among the most naturally radioactive food known are brazil nuts, with activity levels that can exceed 12,000 picocuries per kg.[9][10]
It has been suggested[11] that since the body homeostatically regulates the amount of potassium it contains, bananas do not cause a higher dose. However, the body takes time to remove excess potassium, time during which a dose is accumulating. In fact, the biological half-life of potassium is longer than it is for tritium,[12][13] a radioactive material sometimes leaked or intentionally vented in small quantities by nuclear plants. Also, bananas cause radiation exposure even when not ingested; for instance, standing next to a crate of bananas causes a measurable dose. Finally, the banana equivalent dose concept is about the prevalence of radiation sources in our food and environment, not about bananas specifically. Some foods (brazil nuts for example) are radioactive because of radium or other isotopes that the body does not keep under homeostatic regulation.[14]
- ^ http://www.ehs.unr.edu/ehs/LinkClick.aspx?fileticket=EgZI00myQRM%3D&tabid=62&mid=615
- ^ Weston, Luke. (2007-07-25) banana dose « Physical Insights. Enochthered.wordpress.com. Retrieved on 2010-10-19.
- ^ CRC Handbook on Radiation Measurement and Protection, Vol 1 p. 620 Table A.3.7.12, CRC Press, 1978
- ^ Issue Brief: Radiological and Nuclear Detection Devices. Nti.org. Retrieved on 2010-10-19.
- ^ Radiation and Risk. Physics.isu.edu. Retrieved on 2010-10-19.
- ^ A Brief Review of the Accident at Three Mile Island
- ^ Radiation. Risks and Realities, US Environmental Protection Agency
- ^ [1][dead link]
- ^ Brazil Nuts. Orau.org. Retrieved on 2010-10-19.
- ^ Natural Radioactivity. Physics.isu.edu. Retrieved on 2010-10-19.
- ^ Bananas are radioactive—But they aren’t a good way to explain radiation exposure. Boing Boing. Retrieved on 2010-10-19.
- ^ Rahola, T; Suomela, M (1975). “On biological half-life of potassium in man”. Annals of clinical research 7 (2): 62–5. PMID 1181976.
- ^ Environmental Health-Risk Assessment for Tritium Releases at the NTLF at LBNL: Chapter 2. Lbl.gov. Retrieved on 2010-10-19.
- ^ Brazil Nuts. Orau.org. Retrieved on 2010-10-19.
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Another fun fact about bananas – they have five sides. Useless trivia, I know.
I do like to tell people about bananas and the “banana-equivalent dose” whenever they start to rant about how evil radiation is, etc., etc.
Better with a picture (ranges of radioactive doses):
http://lowdose.energy.gov/images/ig_pics/027_dose-ranges-sievert.jpg
(from http://lowdose.energy.gov/imagegallery.aspx)
Get your elbows off the table (granite countertop). One of the best kept secrets for many decades up to recently was the radioactivity of granite building stone – notably the red and pink varieties which are high in potassium feldspar and mica. Some contain uranium that would be economic ores at approximately $100/lb for U3O8 (Indian Red from India I seem to recall was one of the high level ones). Working in a granite quarry one gets a full measure of the radioactivity. The Canadian Precambrian Shield has alternating volacanic and granite belts, the latter making up perhaps 75% of the area – all radioactive to a measurable degree. Even a spoonful of soil has all 92 elements in it so lets keep our cool – we must be in equilibrium with all this stuff around us. The link is for Czech building materials but applies for the whole world.
http://bing.search.sympatico.ca/?q=radioactivity%20in%20building%20stone&mkt=en-ca&setLang=en-CA
“All building materials that originate from minerals always contain a certain amount of radionuclides. These are mainly potassium, uranium, thorium and the radionuclides that are created as their radioactive decay chains. Of these, the most significant is radium (Ra-226). The Ra-226 presence in building materials causes exposure to persons living in dwellings – either by inhalation of radon daughters that decay from radium and release from the building material to indoor air, or by hard gamma radiation that releases from the building material as a consequence of the radioactive decay of the natural radionuclides to be present.”
Many years back Blaine County in Idaho, home to Ketchum and Sun Valley and hundreds of idle rich declared itself a Nuclear Free Zone.
We wondered how that worked out at the hospital and other medical centers among several location for potential radiation sources.
Next time you are outside on a clear night look up…
Nuclear energy is the single most common naturally occurring phenomena in our universe
What amount of radiation does your body get from the potassium it contains and from others you live with? We ought to become hermits, but only after ensuring our cave is not carved out of potassium-rich granite, sandstone or shale.
As a nuclear power plant worker, it always amazes me just how little people understand the concepts and actual exposure levels resulting from the plants. The sailors working on the flight decks of Aircraft Carriers routinely receive significantly higher doses from cosmic radiation and shine from the jets than the folks working in the nuclear reactor plant below deck.
The human body is a system. It regulates itself. It has mechanisms to repair damage done by radiation. There is controversy about whether these mechanisms respond (increase in activity) when a person is exposed to radiation. It is possible that we live in a world with too little radiation. Sounds similar to CO2.
I particularly like the comparison between the ‘radioactive’ milk after TMI and bananas. Unless my arithmetic is off, you’d have to drink about seven gallons of the milk to get the same dose as you would from eating one average banana. …or if you made a banana shake with that milk, less than 1.5% of the total dose you’d get would come from the milk.
gcb says:
February 16, 2011 at 10:05 am
“Another fun fact about bananas – they have five sides. Useless trivia, I know.”
I believe you would enjoy doing the old trick with a banana where you stick a needle into one of the ridges of the banana and swing the needle back and forth to slice the banana before peeling – my grandkids think I’m majic.
Thanks Anthony for a well articulated note of radiation common sense.
For non-Americans some unit translation:
The average radiologic profile of bananas is 3520 picocuries per kg, or roughly 520 picocuries per 150g banana.[3] The equivalent dose for 365 bananas (one per day for a year) is 3.6 millirems (36 μSv).
1 curie = 3.7 E+10 becquerels (Bq). One Bq is one disintegration per second.
So 1 picoCurie (pCi) = 0.037 Bq. (One disintergration per 27 seconds.)
So a banana contains 520 pCi or 19 Bq.
Another way to consider the concept is by comparing the risk from radiation-induced cancer to that from cancer from other sources. For instance, a radiation exposure of 10 mrems (10,000,000,000 picorems) increases your risk of death by about one in one million—the same risk as eating 40 tablespoons of peanut butter, or of smoking 1.4 cigarettes.[5]
This is the orthodoxy, but the risk of cancer from 10 mrems (100 uSv) is zero. There is a threshold of in the 10-100 mSv (mSv, not uSv) below which radiation causes zero cancer risk and probably slight health benefit.
Some beta-emitting isotopes are more
dangerousto be considered than others, if eaten. Some calcium isotopes are strong beta emitters, accumulate in bone, and have long half lives, so they sit and emit. A by-product of some of these (called a decay product) is an alpha-emitter. This radiation be a good or a bad thing, as mentioned, depending on one’s immunity. Sulfur 35 is actually dangerous, since it accumulates in important tissues, especially gonads.Truth is, that looking at volcano belching chlorine and fluor-rich smoke is “amazing”, while the steam coming off the cooling tower is “dangerous pollution”. Or three molecules of CO2 per 10,000 other molecules from 1750 are natural, but the fourth is again a “dangerous pollution”.
Now understand how even almost harmless dirty bomb will make havoc in a modern society. Radiation, run!!
Elvis was fond of banana and peanut butter sandwiches. He was doomed, even without the drug abuse.
Nostalgia: So my old C-D radiation survey meter is not the only one left? From the days of fallout shelters and “What to do in case of Nuclear attack” movies? Mine doesn’t click, only has a meter. If it moves off zero, say goodbye.
Teller said something about getting more radiation from two women than from a nuclear power plant, so sleep with only one at a time.
I think Chernoble killed more folks than TK’s car, so the bad joke may be obsolete.
Run your counter down any pre-stressed concrete surface and listen to it hum. Used to do it when I was teaching first year geology to demonstrate the levels of radiation in the world around us. The teaching laboratory walls were alive with the sound of radiation. In fact most concretes will do it but pre-stressed is nice and high in potassium – as is the crust of our planet.
And when it comes to high natural levels of radiation that population of Niue have been living with it for hundreds of generations. The limestone of the island is replete with both uranium and thorium. There is not a mutant in sight among the animals or plants either on land or in the Pacific.
“There are about 1,200 beta particles per second produced by the decay of 14C. However, a 14C atom is in the genetic information of about half the cells, while potassium is not a component of DNA. The decay of a 14C atom inside DNA in one person happens about 50 times per second, changing a carbon atom to one of nitrogen.”
http://en.wikipedia.org/wiki/Background_radiation#Radiation_inside_the_human_body
Jeff says: “don’t tell Michelle Obama, she’ll ban bananas …”
Don’t tell Obama, either–He’ll want to regulate food by Federal fiat. Oh, wait…
Back in my commercial nuclear power days, we would periodically get whole body scans to determine if we had exposure. One woman came up very (VERY) high in K-40. There was quite a bit of excitement surrounding whole thing until it was recognized she ate two bananas with her lunch….daily.
Back in the ’80’s Psychology Today had a feature articla on common fears compared to the actual risk the feared phenominon represented. Everything from carcinogens in peanut butter (near the top risks) to Nuclear Power Plant emissions. Car travel vs. Air travel vs walking around a city block. The lowest risk, represented in the average days the risk shortened ones life-span, was living next door to a nuclear power plant.
Toronto, Ontario has a science museum with a few articles in a glass box. The items included a red glazed plate, a brick, a cement block, and a pound of dirt from the perimeter of the Three Mile Island Unit 2 containment building. There was a geiger counter, much like the one pictured above, for masuring relative radiactive emissions. Nothing from the dirt, but I have to admit, I’ve decided not to buy any red fiesta ware.
I never knew that bananas are beta emitters. I don’t know, but I’ve been told you can shield plutonium (an alpha emitter) with a sheet of notebook paper. On the other hand colbolt60 can shine gamma radiation right through your very soul. I live in the Rocky mountains at 7,000 ft above sea level. We’ve got lots of granite around. I don’t even think about my radiation exposure but I’m quite sure it’s higher than most of the US population. In fact, I was told when I first moved here that the road was paved with uranium mine tailings.
A lot of folks would be shocked by the natural radiation that is emitted by the planet’s oceans (not to mention the mercury!). Radiation is ubiquitous. Ironically about your only escape is to spend 6 months aboard a submerged nuclear powered submarine. These guys have extremely low radiation exposure.
bubbagyro – The only beta emitters for Ca are Ca-46 (0.004% abundance) and Ca-48 (0.187%). They are not a significant source of radiation. Perhaps you meant Sr-90, which is a byproduct of nuclear fission. Tons of were emitted in the Chernobyl accident and since Sr and Ca are in the same group, one will replace the other in bone structures. Sr-90 has a half-life of 28.8 years and is a principle cause for bone cancer to those exposed to it.
A pal of mine arrived in JFK from LHR a few years back and set all the alarms off. Even after a strip search they still couldn’t work it out. Finally they let him offer an explanation, which was that he had been to hospital a day or so previously to have a barium meal, related to an ongoing medical investigation.
All the more embarrassing as he was the skipper of the flight!
Makes you think!
I had never heard the banana explanation before – nice one Anthony.
I read a few years ago that people who live in slightly elevated radiation environments (natural background radiation) are healthier and less prone to ailments like cancer. One city mentioned was Aberdeen Scotland, where the homes are largely built grom local grey granite that has a low level of radioactivity. The article suggested that American concern with low levels of radon may be misplaced.
Denver has 3x the normal radiation exposure due to its proximity to the mountains. Yet cancer rates are lower there than on average. Who would have thought? Current theory alleges that the cellular DNA repair mechanisms are used more which allows for less errors to accumulate before repair, yielding more intact DNA.