But there are other, less energetic processes that can create smaller amounts of gamma rays. Sometimes, atomic nuclei just get bent out of shape, and when they do, they can shift themselves back into shape and release some gamma rays through a process called radioactive decay.
Radioactive decay is something humans are very familiar with. Radon gas is dangerous because it can cast off radioactive particles inside the lungs, and carbon-14's radioactive decay patterns can be used to determine how old something is.
Potassium, on the other hand, naturally releases gamma rays and potassium is a very common element. Hayes says common elemental sources like this, as well as radiation bouncing in from space, expose us to gamma radiation every day.
He found that bananas, for example, emit gamma rays at 0.17 micrograys—a unit of radioactive energy an object releases, divided by the mass of the object—per hour. Bricks clocked in at 0.15 micrograys per hour, while avocados and the radioactive components of smoke detectors each let out 0.16 per hour.
Without the proper context, you could see those figures as anything from underwhelming to alarming. Hayes measured uranium ore, the unrefined fuel for nuclear reactors, and found that it emits 1.57 micrograys per hour—that's one hundred times as much as an average banana.
Put another way, the United States Nuclear Regulatory Commission (NRC) recommends that even people who work with radioactive material should not be exposed to more than 50,000 micrograys every year. This is the minimum dose that the NRC considers to be dangerous over several years. That would involve absorbing the radiation from 36 avocados, 24 hours-a-day, every day for a year. Or, assuming it takes about 48 hours for food to pass through the human body, you would need to eat 18 avocados a day, or 6,570 avocados over the course of a year to hit that level.
On the other hand, the NRC considers five grays (5 million micrograys) all at once to be a lethal dose of radiation. To put this amount in perspective, receiving this dosage would require the consumption of more than 29.4 million bananas in an hour.
Small sources of gamma rays are all around us, but like the bricks, bananas and avocados, the dose they give us is far from dangerous and barely noticeable. Bad news if you want to banana your way into becoming the Incredible Hulk or use avocados to turn your pet iguana into a pet Godzilla; good news for health and science!