Banana equivalent dose
A banana equivalent dose (BED) is a concept[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. 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 radioactivity is 130 Bq/kg (3 520 pCi/kg), or roughly 19,2 Bq (520 pCi) per 150 g banana.[3] The equivalent dose for 365 bananas (one per day for a year) is 36 μSv (3.6 mrems).[citation needed]
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 0.1 mSv (10 mrem) 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]
Comparison to Three Mile Island
After the Three Mile Island nuclear accident, the NRC detected radioactive iodine in local milk at levels of 0,74 Bq/l (20 pCi/l),[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.
Other foods
Nearly all foods are slightly radioactive. All food sources combined expose a person to around 0.4 mSv (40 mrem) 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 444 Bq/kg (12 000 pCi/kg).[9][10]
The homeostatic objection
 | This section possibly contains synthesis of material which does not verifiably mention or relate to the main topic. (September 2010) |
It has been suggested 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,[11][12] 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.[13]
See also
- Equivalent dose
- Röntgen equivalent man
- Ionizing radiation units
- Roentgen
- Rad (unit)
- Gray (unit)
- Curie
- Becquerel
- Sievert
References
- ^ www.ehs.unr.edu/Documents/RadSafety.pdf
- ^ 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.
- ^ 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.