Radiation vs. Radioactivity

NASA image of Chernobyl in August 2009

As we’ve been reading the news stories since March 11, when the accident at the Fukushima Daiichi nuclear power plant began, we have paid attention to the language used to describe what is unfolding. The multiplicity of measuring systems is particularly off putting to the lay reader, even those of us who remember the news out of Chernobyl in 1986 and Three Mile Island in 1979 (see Monday’s post on the TMI anniversary). We want to start, though, with something more troublesome to us: the lack of distinction in the use of the terms radiation and radioactivity, for those two words really do mean different things.

While there exists no media conspiracy to confuse readers, there does seem to be a malaise about using correct terminology. A straightforward example of this can be found in an article on CNN that details the strenuous and dangerous working conditions that the employees at Fukushima Daiichi are facing. The first paragraph ends with the following sentence: “They have one blanket, no pillows and a leaded mat intended to keep radiation at bay.” The third paragraph, likewise, ends with a focus on the risk: “They’ve been hailed as heroes risking their lives by braving high levels of radiation as they work to avert a nuclear meltdown.” But the risk is from radioactivity, not just any old radiation. It’s not until the fifth paragraph that “radioactive water” is mentioned. Radiation is mentioned again and again as the article goes on (radioactivity is not), as if it is interchangeable with radioactivity, as if the two words mean the same thing.

Another recent example is that of Ann Coulter’s appearance on The O’Reilly Factor. The combative Coulter said, “Radiation is good for you.” She cites selective surveys of cancer rates and a theory about hormesis, or beneficial effects of radiation. Coulter and O’Reilly banter back and forth, making overarching statements without recognizing fine distinctions or defining what they mean by the term radiation. The studies by Bernard Cohen that Coulter finds compelling address only low-dose exposure, for instance. The conversation fails to recognize that the body’s response to exposure to radioactivity varies from person to person and that when we talk about risk, it’s statistical risk.

But the real problem is that Coulter means radioactivity when she says radiation. Pundits who pick up her sound bite can make fun of her both because radiation is indeed a good thing in many instances and also because radioactivity is indeed a bad thing in many instances. By muddling up the terminology, she gives folks lots to argue about without allowing anyone to argue about exactly the same thing.

EM Spectrum

For this post, we want to focus on the most basic slipping of the media’s tongues. Coulter wants to instigate argument, but news reporters want to convey information. So what exactly is radiation?  Radiation covers an enormous range of physical processes. Most of us have heard of the electromagnetic (EM) spectrum, probably in seventh-grade science. When you turn on your radio, low frequencies on that EM spectrum carry the tune. Radio waves are energy that we can use to transmit information, including sound. Most of us are familiar with a wide range of radiation through the tools and devices that are part of our everyday life.

Turn on any of the 100-watt light bulbs in your household. By looking at the light bulb and placing a hand near it, you can physically sense that it is producing two types of radiation: visible light and heat. In fact, most of what is given off by incandescent household lighting is heat. Typically less than 10% is given off as visible light. That’s one reason why the United States is shifting from incandescent to compact fluorescent light bulbs; too much energy is being used to produce heat, when all we really want from our light bulbs is that slice of visible light in the spectrum of radiation.


And within the EM spectrum of visible light, we have different colors. Didn’t we all learn ROYGBIV as a way to remember the visible light spectrum from red to violet? And why that order? Because each color has a different frequency in the spectrum, from the long wavelength (and lower frequency) of red to the shorter wavelengths (and higher frequencies) of blue, indigo, and violet.

Microwaves, cell phones, and lots of other devices we use every day also produce and manipulate radiation. Radiation means what it sounds like: energy that radiates out from a source through space or matter, no matter what kind of energy that might be. But this isn’t the radiation being discussed in the media covering Japan. What the media should be discussing when they talk about the exposure of nuclear power plant workers or about the levels in water leaking into the underground tunnels is radioactivity.

Gamma Decay

Radioactivitymeans something very particular, if you’ll excuse our pun. That’s the emission of particles or certain electromagnetic rays during nuclear decay. (Don’t worry if you don’t understand exactly what we mean by nuclear decay, because we have enough to say about that for a post next week.) Radiation, at the higher frequency end of the spectrum, can break chemical bonds, strip off electrons, and even break up the nuclei in atoms. When nuclear decay or nuclear fission processes occur, an ion—a positively charged particle—and an electron result. This is the process that is occurring when we speak of ionizing radiation. The highest energy radiation on the EM spectrum—shortest wavelengths, highest frequency—is x-ray and gamma radiation. This is also radioactivity.

The danger at Fukushima Daiichi is from radioactivity, a particular kind of radiation. When the news reports iodine-131 in the Tokyo tap water, cesium-137 is the sea water, and traces of plutonium outside the boundaries of the nuclear power plant, they are reporting measurements of radioactivity. Monitoring systems are measuring the level of radioactivity emitted by these elements and isotopes. But radiation and radioactivity refer to distinct things and are measured in distinct ways.


3 thoughts on “Radiation vs. Radioactivity

  1. Still reading the post, but I wanted to comment on the light bulb comments. Really a great and easy explanation of why we should switch bulbs. It’s not the amount of energy wasted, but why it’s unnecessary to waste energy on a byproduct of the generation of light. Thanks!

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