So…I’m a radiation safety professional, which means that I have a bunch of radiation detectors at my home. And every now again I turn on my meters to see what they read – sometimes I’m teaching a class via Zoom, sometimes I’m checking to make sure the instruments are working properly, I might be checking my own radioactive materials that I use for teaching, or sometimes I’m just curious. The other day I was making some measurements and I noticed they were a little higher than I’m used to seeing and it made me think about all the ways that I encounter radiation on a regular basis. And, being a writer, it occurred to me that it might be worthwhile to share with you the sorts of things I run across.
We can start with natural background radiation – every minute of every day we are all exposed to radiation from nature. Potassium, for example, is vital to the proper operation of our bodies (including our hearts and other muscles)…and about one potassium atom in 10,000 is radioactive, exposing us to radiation from within our own bodies. Not only that, but we also have small amounts of radioactive carbon and hydrogen in our bodies – these are formed by cosmic ray interactions in the upper atmosphere and they filter on down to sea level where we breathe them, drink them, and eat them. Incidentally, a colleague of mine once calculated the radiation he received from potassium in his wife’s body due to, as he put it, “spending about 25% of his time at a distance of less than 1 meter from her” (when I asked him about installing lead shielding, he pointed out that the toxicity of lead would be more dangerous than that extra radiation exposure).
The potassium in bananas, salt substitutes, and other high-potassium foods gives us a little radiation as well – as do the traces of radium found in Brazil nuts. Add to that scant amounts of uranium, thorium, radium, and a few other natural heavy elements that lodge in our bones (mostly from breathing and ingesting dust) and we get about 40 mrem every year from radioactivity that’s a part of our bodies.
There’s also cosmic radiation – some from our Sun, but most that originate in exploding stars elsewhere in our galaxy. In fact, every time I fly I can see cosmic radiation exposure increase as we climb to cruising altitude – in 2019 I flew from NYC to Seoul South Korea on a flight that took us over the North Pole and I saw cosmic radiation levels climb even higher as we flew increasingly northward.
Then there’s still more radiation from the rocks and soils as well as from things made from rocks and soil (granite countertops, bricks, concrete, and so forth) – these each account for just under 30 mrem annually. And the radon emanating from the ground exposes us to another 200 mrem a year, although this is variable, depending on the amount of uranium in the soil and the underlying bedrock. All told, we get about 300 mrem (more or less) from natural sources and from things that are built or made of natural materials. And that’s just the start!
In my apartment I’ve got a lot of radiation sources – some of these are pretty common, some are not, but I don’t need to have a radioactive materials license for any of them. There’s the granite countertop that my landlord installed, for example (granite contains potassium as well as uranium and thorium), as well as the brick my building is made of (brick is made of clays that often contain potassium). I’ve got my collection of radioactive rocks and minerals as well – I picked up most of these at rock and mineral shows or shopping online – and I also have a bunch of consumer products, most of which I bought online. Thoriated welding electrodes, “Vaseline glass” and Fiestaware plates colored with uranium, a stainless-steel soap dispenser contaminated with radioactive cobalt, and a few other things.
There used to be even more than this – I recently got a “Revigator” that’s almost 75 years old. The Revigator is a ceramic crock that’s lined with what looks like concrete…except that the concrete is impregnated with radium-bearing rocks. The premise was that people would fill this with water and, overnight, the radium would “invigorate” the water with energy that, when drunk the next day, would improve one’s health. I only made a few measurements on my new acquisition, but it looks like the most radioactive thing in my collection. Having said that, it still gives off too little radiation to pose a risk to me – especially since it sits about six feet from my desk. Another “back in the day” source of radiation were the cathode ray-type television sets and computer monitors – they never gave off enough radiation to cause problems, but they did give off radiation.
Interestingly, a few months ago I turned on one of my radiation detectors and noticed that dose rates were higher than I’m used to seeing. At the time I was borrowing a gamma spectroscopy device from a colleague – I identified the nuclide as I-131, which is commonly used for treating thyroid cancer and other thyroid diseases. My guess is that one of my neighbors was having thyroid problems – I probably could have figured out which one by checking the walls, floor, and ceiling…but decided to leave my neighbors with a bit of privacy, especially since the dose rate wasn’t at all high enough to be a concern (for me or for them). Of course, nuclear medicine is hardly rare – when I was working for the police (as a civilian scientist) I made hundreds of radiation surveys, both on the ground and from the helicopter, and we picked up nuclear medicine patients on our instruments all the time.
This is a photo of my radiation detector display when we were flying circles over the Brooklyn Bridge and the East River. The high readings showed up when we were over the bridge.
Getting back to building materials, granite’s a big one – due to the geochemistry of uranium, thorium, and potassium (and due to the way that minerals crystallize in magma chambers – https://en.wikipedia.org/wiki/Bowen%27s_reaction_series) many light-colored igneous rocks, including the gray, pink, and red granites, have more radioactivity than many other types of rock. Enough, in fact, to sometimes set off radiation alarms for ground-based surveys and to show elevated dose rates from the air. Flying over the granite Brooklyn Bridge, we always saw higher readings than when we flew over the East River; flying over cemeteries gave us higher readings due to all of the granite headstones.
I’ve also been called on to respond to other sources of radiation – loads of ceramic tiles for example that were coated with glaze that included uranium for the bright colors (mostly yellow and orange) it could produce. And then there was a time we detected radiation from industrial radiography – using radioactivity to take images of pipes, welds, structural steel, and the like – anyplace with a lot of construction and a lot of welding is likely to have radiography taking place on a regular basis. Here, too, the radiation levels aren’t nearly high enough to cause problems, providing the radiographer is doing their job properly – in the US and Europe that’s likely to be the case, but there have been radiography accidents in a number of nations over the years.
I teach a lot of classes on radiation safety – many of my students work in industries that use radioactive sources to gauge the levels of tanks or to control various manufacturing processes. If you put anything between a radiation source and a detector, the radiation levels drop – the more material, the more the levels go down. So radiation levels from a source at the top of one side of, say, a tank filled with caustic chemicals will suddenly drop when the tank fills too high, letting operators (or automatic systems) know it’s time to stop filling the tank; a source at the bottom of the tank will keep the tank from emptying out and possibly ruining a pump. Similarly, I’ve seen radioactive sources used to check the levels of beer bottles on an assembly line, to control the thickness of paper or steel, to check the density of soil, even to detect clogged conveyor belts at a gold mine in Nevada. While none of these expose me on a daily basis, they’re examples of how radiation and radioactivity are used on a daily basis in the nooks and crannies of industry.
In fact, radiation is present in all sorts of society’s nooks and crannies, whether it’s the natural radiation we’re exposed to the mountains, in our basements, at high altitudes, or in the bunch of bananas we stash in our kitchens; in our workplaces and in the workplaces of others; or in the hospitals and clinics and contained within the patients who have visited them.
What’s interesting is that people are exposed to more or less radiation depending on where they live, where they work, what they buy, what they do for a living, and so forth…but these don’t seem to affect the rates of cancer. This suggests that the radiation we run into on a daily basis isn’t likely to hurt us.