Small Amounts of Gamma Rays Come from Everyday Objects
October 13, 2016
Gamma rays are the most powerful and potentially destructive type of electromagnetic radiation. This particularly nasty product of atomic bombs and the sun’s energy-making process can shred DNA, pick molecules apart piece-by-piece, make plants wither and die and even cause cancer.
Like most forms of radiation, however, the dose is as important as the energy of the waves. New research from NC State University has shown that we are exposed to gamma radiation every day in low doses, and that some very familiar objects emit safe levels of gamma radiation.
Robert Hayes, nuclear engineering professor at NC State and senior author of the study, said in a press release that understanding the radiation that we experience every day could reduce some of the fear and stigma toward radiation.
“We did this study because understanding how much radiation comes off of common household items helps place radiation readings in context," Hayes said. "It puts things in perspective."
When atoms change shape, they absorb and release energy. Atoms release gamma rays when the protons and neutrons in their nuclei shift from an unstable form to something more stable. This happens during nuclear fusion, the process of combining small nuclei that power the sun, and nuclear fission, the process of breaking large nuclei into pieces that power nuclear plants.
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!
Daniel Lane covers science, medicine, engineering and the environment in North Carolina.