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banana equivalent dose (abbreviated BED) is a unit of radiation exposure, defined as the additional dose a person will absorb from eating one banana.
The concept is based on the fact that bananas, like most organic materials, naturally contain a certain amount of radioactive isotopes—even in the absence of any contamination due to human nuclear endeavors. The banana equivalent dose was meant to express the severity of exposure to radiation, such as resulting from nuclear power, nuclear weapons or medical procedures, in terms that would make sense to most people.

The concept probably originated on the RadSafe nuclear safety mailing list in 1995,[original research?] where a value of 9.82×10−8 sieverts or about 0.1 μSv was suggested for a 150 gram banana.

Watt's up with that - The average radiologic profile of bananas is 3520 picocuries per kg, or roughly 520 picocuries per 150g banana. The equivalent dose for 365 bananas (one per day for a year) is 3.6 millirems (36 μSv).

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.
A banana contains naturally occurring radioactive potassium.


Japanese radiation readings:

Monitoring of radiation levels on the spot is ongoing. At point MP4, where a reading of 1,015μSv was detected yesterday, a radiation level of 44.6μSv was recorded at 00:30 this morning, and a level of 36.7μSv at 6:00am. After the start of venting around 9:20, a reading of 76.9μSv was recorded at 9:20 and of 70.3μSv at 9:30.

The radiation spiked up to 30 bananas a day (2 days ago) and then fell back down to 1 to 2 bananas per day.

UPDATE: Unit 2 has had serious damage and radiation levels on the edge of the plant compound briefly spiked at 8217 microsieverts per hour but later fell to about a third that. Normal annual doses for a year will occur in one day.



After the Three Mile Island nuclear accident, the NRC detected radioactive iodine in local milk at levels of 20 picocuries/liter, 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).

Further Reading

Radiation and Risks - Various amounts of normal radiation

1400 millirem for a gastrointestinal examination series (14,000 microSv)
200 millirem for one year in an average house from Radon (2,000 microSv)
360 millirem average annual dose for someone in the USA (3600 microSv)
660 millirem per year for your whole career might have a life expectancy loss of 15 days
1360 millirem per year for your entire working career might have an expected loss of 51 days
A manufacturing career reduces life expectancy by 40 days
100 rem definitely causes damage (10000000 microSv, 1 Sv)

Note: This is not a "nuclear accident". It is damage from an earthquake and tsunami. The reported sweeping away of four entire trains, including a bullet train which apparently disappeared without a trace, was not labeled “the third worst train accident ever".

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