Posted in Science & Nature

Banana Equivalent Dose

No form of energy has been more feared or creatively explored in science fiction (e.g. Godzilla) as radiation, yet the layman tends to know little about the actual properties and effects of radiation. The word “radiation” is commonly associated with things like Chernobyl, mutation and cancer. However, most people only know that radiation is “bad” while not knowing exactly how and why it is dangerous. Radiation is essentially high-frequency light which can deliver a large dose of energy (just like how microwaves cook food and sunlight can burn paper when focussed through a magnifying glass). When this high-dose of energy passes through living organisms, it damages the DNA in cells, potentially causing irreparable damage. This can lead to mutation and disruption of cell division (which can lead to cancer) or cell death (which is why radiation is ironically used to kill cancer cells).

The more technical question is “how much” radiation is harmful. For example, how much more dangerous was the Chernobyl incident compared to an x-ray? Like many other things in science, radiation is measured using an internationally universal unit called the Sievert (Sv). The radiation received from standing next to the Chernobyl reactor core after meltdown was 50Sv, while a chest x-ray is 20μSv (1000μSv = 1mSv, 1000mSv = 1Sv). Therefore, the Chernobyl incident could be considered to be as strong as 2.5 million chest x-rays. Although there is great variation, it is considered that a dose of 400mSv can cause symptoms of radiation poisoning, while 4~8Sv of radiation will lead to certain death.

Fascinatingly, radiation is not an uncommon thing. Radiation is all around us, with an average person receiving about 10μSv of background radiation per day just by living on Earth. Ergo, two days of walking around gives you the same amount of radiation as a single chest x-ray. A CT scan gives out a significantly greater dose of radiation at about 7mSv (approximately 350 x-rays or a year’s worth of background radiation).

However, the Sievert is a unit that is difficult to understand. Thus, some scientists devised a clever, humorous equivalent unit called the banana equivalent dose (BED). Bananas contain a certain amount of radioactive isotopes (radioactive potassium), making them technically radioactive. A banana contains 0.1μSv of radiation. Ergo, a chest x-ray is the equivalent to eating 200 bananas, a CT scan is 70000 bananas, while the Chernobyl incident gave people nearby a dose of roughly 500 million bananas.

The banana equivalent dose is a rather useful (and hilarious) way of comparing the danger of radiation from different sources. The next time you go to hospital for an x-ray, just picture 200 bananas being shot through your chest.

Posted in Psychology & Medicine


In 1967, a group of scientists designed an experiment where five monkeys were put in one cage with a ladder in the middle and a banana suspended over it. When a monkey tried to climb the ladder to reach the banana, it was hosed down with ice cold water to discourage it. However, at the same time the four other monkeys were sprayed as well. This was repeated until the monkeys were conditioned not to climb the ladder as it meant being blasted by cold water. Interestingly, even when the reward was tempting enough for a monkey to brace the cold water and climb the ladder, the monkey was swiftly taken down by the other monkeys – fearing the cold water – and was punished by a beating. This further discouraged the monkeys from climbing the ladder even when the researchers stopped spraying the monkeys with water.

The researchers then substituted one of the original monkeys with a new monkey who had not been in the cage before. This new monkey immediately noticed the banana and started to climb the ladder. The other monkeys saw this and responded with rage, enforcing their unspoken “rule” of never climbing the ladder. The new monkey quickly learned that climbing the ladder was a bad thing.
The researchers substituted another original monkey for a new monkey and the same thing happened. They repeated this until all monkeys were replaced.

When they substituted the last monkey in (number 10), the cage was already filled with “new” monkeys who had never been hosed before, but nonetheless knew not to climb the ladder. When the monkey was punished for climbing the ladder, it gave an expression that seemed to question why he was being punished. The other monkeys did not know why; none of them had been punished with cold water and only knew that the other monkeys would beat him up. Even though none of them knew why the punishment was required, they dished it out regardless. The rule had been engrained into the mob, with each monkey following it without any logical reason.