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19 March 2011 @ 02:53 pm
Bananas  
Bananas are the most radioactive of all fruits, mainly due to trace amounts of potassium-40 found in naturally occurring sources. This is so well known that there is a concept known as a Banana Equivalent Dose, or BED.

So, to give some context to the whole Fukushima Daiichi disaster, I thought I'd give some banana equivalents of the various numbers I've seen from various sources. Hopefully I've got the numbers right:

12 bananas per hour (300 bananas per day) -- this is the highest level I've seen reported from the Tokyo area (specifically Saitama). This is a completely insignificant amount, and was transient in any case (when the winds were least favorable). If anything measurable ever reaches the United States, it's unlikely to even reach this (very low) rate.

1700 bananas per hour (40,000 bananas per day) -- this is the highest level measured in Fukushima outside of the plant. While this is a lot of bananas, it's still not enough to show any immediate or long-term health effects for short periods of exposure (say, a day or two). However, if this dosage were extended (say, for weeks or months), things are a bit murkier and concern would be warranted. Fortunately, these areas have already been evacuated.

30,000 bananas per year -- average natural background exposure per year for the average American.

90,000 bananas per year -- cumulative exposure for a flight crew flying the New York to Tokyo route. (I made a mistake here before, I thought this was one flight.)

90,000 bananas -- typical chest X-ray

60,000 - 180,000 bananas -- chest CT scan

1,000,000 bananas -- that's a lot of bananas. This is also the highest level any of the emergency workers at the plant has so far been reported to be exposed to. This is a worrisome level; while this is the highest level generally allowed by some (not all) nuclear regulatory agencies in emergency situations, this is still five times the yearly limit generally allowed for nuclear workers, and is about the lowest level that has been clearly linked to additional risk of cancer (I'm not sure what the additional risk might be, but presumably still low, I'd hope). This is generally below the level where any immediate adverse effects are felt.

[Incidentally, the only reported fatality so far was due to a crane accident during the actual earthquake itself; most reported injuries to date have been due to injuries from that or directly from the hydrogen explosions, the other contamination cases were with much lower dosages than this.]

10,000,000 bananas -- this level is clearly in the range of radiation sickness. Recovery is probable, but not assured, with an additional long-term risk of cancer. 10,000,000 bananas per hour is also the highest level that was (briefly) recorded inside the plant (outside of the reactors), but this level quickly receded, and no one was directly exposed to it that long. It was, however, enough to order a temporary evacuation.

100,000,000 bananas -- death from radiation sickness all but certain.

3,000,000,000 bananas per hour -- highest levels of radiation at Chernobyl plant during that disaster. That's a bloody awful lot of bananas.

2,650 bananas per hour -- current level of radiation near the plant as of 18 March (and dropping).

Of course, the types of radiation (say, alpha vs. beta vs. gamma) matter a lot, as do the specific isotopes carrying the radiation. The most dangerous contaminant is iodine-131, due to the fact that it's concentrated in the thyroid gland. However, it also has a very fast half-life of 8 days, so the danger from it disappears more quickly than many other contaminants; it's the main thing that food is being tested for in Fukushima.

Things seem to be more or less under control now, fortunately.

ETA: apparently the BED page on Wikipedia has been the victim of edit wars and who knows what else since it started getting more attention after the accident, so I have no idea what it might say by the time anybody reads it.
 
 
 
Elpergamond on March 19th, 2011 07:30 pm (UTC)
Brilliant! Finally a unit we can relate to ^.~
Tully: dangertully01 on March 19th, 2011 09:14 pm (UTC)
Yeah, context is important. Especially when people are running in circles babbling hysterically.

Dustybigmog on March 19th, 2011 10:23 pm (UTC)
Even with a nice unit of bananas, it's still hard to visualize large numbers of them. It's not something humans are particular good at which is why large numbers are often thrown around to astound people. I picture 1700 bananas; would they fit into a van? Honestly I'm not sure.

Douglas Triggs: moondoubt72 on March 19th, 2011 10:48 pm (UTC)
Well, one reason I did this is because it's fairly easy to compare 10,000,000 bananas to 1,000,000 bananas... That's a factor of ten, the math isn't hard. Because, well, one of the things that was annoying me about the coverage (even the good coverage) is that it was constantly mixing scales... Sometimes Sieverts (Sv), sometimes mSv, sometimes μSv, sometimes even nSv when they're trying to make it sound really bad. And sometime other unit scales altogether, like REMs (which is like .01 Sv or something I can't remember). It's hard to keep things straight.

The other point, well, yeah, bananas.