You may have read about everyday objects setting off radiation alarms at border crossings between the US and Canada and Mexico. Newsweek has an article describing how medical radiation treatments (e.g., bone scans) may lead to traveling delays when they trigger radiation sensors. When the sensors are tripped, border officials conduct more intensive inspections to make sure you aren't carrying nuclear weapons. There are other ways to set off the alarms. Do you carry kitty litter in your car to help provide traction in icy weather or to absorb oil? It's slightly radioactive. Do you have tile or granite in your vehicle for a home improvement project? It has a relatively high radiation signature. Do you have a lot of bananas? They are also slightly radioactive.It's pretty easy to understand why tile, granite, and kitty litter are radioactive. They contain low levels of minerals that naturally decay. Bananas are radioactive for a similar reason. The fruit contains high levels of potassium. Radioactive K-40 has an isotopic abundance of 0.01% and a half-life of 1.25 billion years. The average banana contains around 450 mg of potassium and will experience about 14 decays each second. It's no big deal. You already have potassium in your body, 0.01% as K-40. You are fine. Your body can handle low levels of radioactivity. The element is essential for proper nutrition. If you have a banana in your car for your lunch you aren't going to set off a Geiger counter. If you carry a produce truck full of them, you might encounter some problems. Ditto for a truck of potatoes or potassium fertilizer.
I guess my point is that radiation is all around you. After I read the Newsweek article I clicked off-site for more information and I found concern (panic?) over bananas being radioactive. Are they radioactive? Kinda. If you set a banana on a detector you won't hear mad clicking. It won't glow in the dark when you turn out the lights. There is a perception that radiation is bad, bad, bad. It's just a part of life. Bricks are radioactive. Anything containing carbon (you) is slightly radioactive. Bananas are radioactive and it's no big thing. Well... except maybe to Homeland Security.
Comments
Oh, dear. One more thing I have to worry about…radioactive travel snacks!
Novel points about banana. But harmless doses
of radioactivity.
Thank You,
Rosario
so what do monkey have in them that there main food itself is banana’s and that they can have soo much of it and not increase there potassium value and get sick…and if they have any special thing, wouldnt it be wise to extract it from monkeys and use it as a medicine for people working in neuclear power plants or decay plants.
If bananas are radioactive then they should heat up the body very soon but even excessive eating doesn’t produce such condition.
It means they are harmless.
Actually, it is a misconception to think that monkeys or primates only eat bananas. They eat a variety of fruits and vegetables just like humans. So they would be no more radioactive than us in that regard.
I love Ur banana article of radioactive isotopes and also Ur reflection on radioactivity as part of almost all mineral containing substances.
Iam a 1/2 vegetarian and consume 3 bananas a day. What do U think???
Thanks a lot Mrs Helmenstine
Best Regards // George
Standard sillyness from the “YOUR GOING TO DIE” croud. The dose is the poison. If you don’t drink any water, you die. If you drink the a lake, you drown and die. If you get no radas from the sun, vitaima D deficency, if you are are in the sun all the time, Skin Cancer. Just don’t worry about it, death is just the perod of life.
so the half life is 1.25 billion years and decays 14 times a second?
are you sure you know what your talking about?
ah, ignorance at it’s very best…if you yourself do not know what you are talking about, do not leave a comment.
half-life is the time it takes for the radioactivity of a specified isotope to fall to half its original value. A decay happens many times from each radioactive particle in a banana (there’s not just ONE radioactive molecule in a banana)
if you’re confused, http://en.wikipedia.org/wiki/Radioactive_decay
Means that 14 potassium atoms decay every second in one banana. 1.25b years is how long it takes for half of any given quantity of potassium to decay.
i like this banana thing and think that you are right and wrong. just because bananas have like 0.01% radioactivity doesn’t mean that they are radioactive
OVER AND OUT
BANANAS RULE THE WORLD
@joe: There are many, many, many, many, many molecules of potassium in 450 mg of potassium.
ever heard of Avogadro constant
— molecules in a mole of any material,,
6.02214179(30)×10 to 23 power mol−1
14 decays per second is not much…
http://encyclopedia.thefreedictionary.com/Avogadro%27s+constant
worry about the economy and drunk drivers… those are critical…….
Yes — but so is just about ANY fruit or vegetable. They all contain Potassium, and a tiny fraction of all Potassium is radioactive. The amount of radioactivity is so small it is almost impossible to measure.
I love the way the media is now making excuses for the radioactivity of our food supply. Never mind….everything was “always radioactive,” geiger counters were just created as a novelty, not to detect radioactivity that’s harmful and unnatrual. They’re trying to ban geiger counters in New York–for the people, of course. It’s in the people’s best interest NOT to know when a nuclear attack has happened. You know, nuclear attacks that pulverize concrete and metal by breaking them down molecularly. I wonder in those nano particals at Ground Zero that was places into trucks of soil made it into the soil of our food supply. Is our food radioactive as well? Oh wait…
Do the math to put things into perspective. If the half life of P-40 is 1300 million years, it’s been there long before man set foot on the planet.
You can argue about WWII bombs which killed 240,000. Say what you will about that; it was war and it was intentional. The widest estimate from an unintentional exposure was Chernobyl is 4000 deaths, and that includes cancer related deaths not directly attributable.
Considering that our life on this planet depends upon a criticality at the center of our solar system, why do so many disclaim the value of naturally occurring activity in our food supply? Well, you can blame the media for that brand of histeria.
It’s important that we respect the power of nuclear physics, and use it to our wise advantage. However, wouldn’t we fare better, if the general public got serious, and did something about alcohol abuse, texting while driving, or smoking. All of these (and dozens of other voluntary activities) take far more lives every day, than radioactivity has EVER taken. Do the research and see for yourself.
Oh, and BTW, cigarettes are radioactive too, moreso than bananas- in addition to the P-40 they contain Polonium 210.
P-40 has a very long half life. It was in the food chain long before mankind got involved. And then, there’s this huge reactor at the center of our solar system, bombarding us with cosmic beams 24/7. So let’s lighten up about what the media does and doesn’t do. After all, they’re the ones most responsible for the mass hysteria regarding radioactivity.
You want something to get serious about? On top of all the other ills associated with smoking, tobacco is radioactive too. You don’t hear much about that. Smokers enthusiastically suck that crud right into their lungs, where particulate radioactivity is deposited to do the most damage.
DUI, use of cell phones and texting while driving, are voluntary activities that take more lives every year, than involuntary radiation exposure has taken in the last fifty. If you want to get excited about something, start at home.
I’m not suggesting that radiation safety isn’t important. Of course, it is, and we owe a debt to those who’ve rightly enacted legislation to preserve our safety.
However, let’s not add to the hysteria playing the blame game. People need to get informed and make wise decisions. At the very least, let’s be intellectually honest about our activism, and focus on pressing problems.
Rad’s well understood and under control, so let’s move on to what’s fixable.
Can anyone tell me how a nuclear medicine technician can actually compare radioactive dye with the radioactivity of a banana?…. Is it me or are our doctors wasting all that time in school, cuz they sure seem to be F-CKING idiots to me!!
you are a goddess Lucy, Carol, and Rosie. Thanks for a chuckle. (I like to suck the sugar off.)
@joe, the math looks a bit off, but not in the way you’re thinking, so let me break it down.
half life of K-40 = 1.248e9 years
natural abundance of K-40 = .012 %
molar mass of K-40 = 39.96399848 g/mol
450 mg * .012% = 5.4 mg
5.4 mg = .0054 g
.0054 g / 39.96399848 g/mol = 1.3512e-4 mol
1.3512e-4 mol * 6.022e23 particles/mol= 8.137e19 atoms K-40
4.0685e19 decay in the first 1.248e9 years
average of 3.26e10 per year
average of 1033 per second
Now I may have made an error in my math, and feel free to point it out if you find one, mind you this was quick and dirty done with the calculator built into windows. So to the layman, a banana is actually considerably radioactive, but you have to consider that K-40 decays into a weak beta particle, so the level of ionization is minimal.
@Chris
Close, but its .012% which is really 0.00012 which works out to about 0.054 mg.
I can’t believe I made such a simple mistake, I blame it on doing that at around midnight. I’m half tempted to re-do the math to correct for that.
Well since it was such a simple mistake, all my numbers are only off by two decimal places, so it’s actually an average of 10.33 decays per second, not far off from the 14 given in the article.
Good work Chris and Mark. However your estimate for number of decays per second will be off because you didn’t figure them using logs. Radioactivity is an exponential decay function. So the number of decays per time unit starts higher and then slowly gets lower over time. So one second now will have almost twice as many decays as one second 1.248e9 years from now. Of course we are interested in the rate of decays for seconds now not 1 billion years in the future. This is what pushed the number to 14 per second.
Almost everything is radioactive. It’s no big deal. It’s actually pointless to display things that are slightly radioactive, since that’s almost everything. Very nice article though. (by 14 times per second I think he means molecules, not each half-life)
Good to see some of us can still do the math – high school was a long time ago for me and I have forgotten a lot of the math (especially logarithms haha)
But man, sure are a lot of ignorant people around too – and they still feel qualified to criticize an article written by someone with a Ph.D lol
And they vote too! 8-|
Avocados??? First bananas, now constant avocados…..life is going to kill us all!!
Last one in please shut the bunker door.
The current Japanese event is a very sad thing. I’ve worked in the US nuclear industry for 25 years. My novel “Rad Decision” culminates in an event very similar to the Japanese tragedy. (Same reactor type, same initial problem – a station blackout with scram.) The book is an excellent source of perspective for the lay person — as I’ve been hearing from readers. It is available free online at the moment at http://RadDecision.blogspot.com . (No adverts, nobody makes money off this site.) Reader reviews are in the homepage comments.
I believe there isn’t a perfect energy solution – just options – each with their good and bad points. And we’ll make better choices about our future if we first understand our energy present.
Hi Chris, Mark: you laid the ground work. Thanks. I will complete the calculation and show you this is exactly rounded to 14 decays per second (if you change your fraction of radioactive K-40 to 0.01 as in the article rather than 0.012 etc I think it will give the exact answer)
Here is the answer:
I take the calculation you two have done correctly, i.e. the 450 gram banana contains 8.137×10^17 nuclei of K-40 (not 10^19 as corrected by Mark)
Now the decay constant or transition probability as one may call it which gives the probability at any time of a single nucleus to decay at any time is w = 0.693/T_half_life. This is obtained by using Heisenberg Uncertainty principle for the nuclear decay. Here decay width which is given as a width of energy and mean life time which is given as a width or uncertainity in time must multiply to h-cross (time – energy uncertainty) Now Mean life is related to half life by the factor 0.693 (69.3% of nucleus would decay in the mean life where as 50% would decay in a half life)
SO the decay probability = w gives the probability or likelihood that any single nucleus will decay or not. SO we know this probability because we know the half life to be 1.25 billion years that is 1.25X365X24X3600X10^9 seconds = 1.25X3.15X10^16 seconds.
Since the banana has 450 grams of Potassium it has as many radioactive K-40 as we just counted, 8.137X10^17 nuclei, at the time of eating. SO the probability of decay is w and you know how many nuclei you got. Multiply them to get the exact number of radioactivity of your banana. Needless to say this product is 14.3.
(8.137X0.693)/(1.25X3.15)X10^(17-16) = 1.43X10 = 14.3
The calculations are correct as you can check, its 450 mg banana not 450 gram…just a typo
I live in Japan. Our bananas are very radioactive.
so what does this mean to the fruitarian, whos staple diet consists mainly of bananas?
is it a concern?
my MIL said humans should eat a lil bit of everything so that if a food is bad youre not eating large amounts.
nice work !!!!!!
My husband got stopped by TSA for carrying a banana in his backpack. Now it makes sense! (not really)
If bananas are radioactive with long half life, if you eat at least one in a day, all your life, how much radioactivity would you accumulate in 80 years of your life?
…and thats how primates evolved into hyper intelligent beings called humans.. radioactive mutation from excessive exposure and consumption of bananas
to Ryan,
wtf – go drown yourself as soon as possible.
Decay plants… goddamnit.
Bananas are not even the fruit with the highest level of potassium…so does that mean mean that young coconuts and dates which have a higher level of potassium have more radioactivity?