You Might Want to Know: What is ionizing radiation? Can it hurt us? How? What does it have to do with nuclear weapons? (Part One)
What is ionizing radiation? Can it hurt us? How? What does it have to do with nuclear weapons?
This story is a little complicated, a little technical. It will take three entries to tell it. But ionizing radiation is part of our lives, inescapably. It’s worth getting a handle on it.
Part I
The “yield” that we are usually given for nuclear weapons refers only to the explosive yield. It is almost always expressed in terms of how many tons of TNT (never less than tons) would be required to produce an equivalent explosion.
But nuclear weapons also yield something ordinary bombs don’t, something it is harder to put a number to or to know the effect of--ionizing radiation.
When the weapons explode, a blast of ionizing radiation is emitted (“prompt radiation”). More arrives later in the radioactive fission products that may arrive in the wind (“fallout”).
When I was a junior-high school student in the 50’s, we heard about this new “radioactivity” that was produced by nuclear bombs. It could be dangerous, we were told. But we were also told that you can’t see it, can’t feel it, can’t taste it or smell it. C’mon, I thought to my twelve-year-old self, how bad could it be?
We should begin by considering what “radiation” is. Radiation has been defined by the Nobel Prize winning physicist Niels Bohr as “transmission of energy between material bodies at a distance.” [Niels Bohr, “Light and Life,” 4]
The energy is transmitted in electromagnetic waves. We don’t have to know here exactly what electromagnetic waves are, only that they are something that can transmit different levels of energy between bodies at a distance.
Much radiation isn’t ionizing. Only radiation that transmits the highest levels of energy is ionizing.
One form of electromagnetic radiation is “thermal” radiation, experienced by us as “heat.” We can feel it on our skin at a distance from the source of it. Because of our experiences with fire, we may think of this infra-red form of radiation as the most energetic, but it actually carries less energy than does the ionizing radiation that we can’t feel. (Radio waves and microwaves carry even less energy and are also not ionizing though microwaves can generate heat, a boon for those of us who like leftovers.)
Nuclear weapons emit a blast of thermal radiation. A stupefying amount of it. The heat generated at the center of a nuclear explosion is, at the start, greater than the heat at the center of the sun. As the heat spreads out from the point of detonation it diminishes but some of the largest thermonuclear weapons can cause third-degree burns twenty miles from the point of detonation. Third degree burns are the deep kind. They don’t hurt because the nerves have been fried.
The “thermal pulse” of some nuclear weapons would reach a good distance beyond where the blast yield would cause damage. But thermal radiation isn’t ionizing.
Another familiar form of electromagnetic radiation that isn’t ionizing is light. We can see light at a distance from its source because it has an effect on the retinas in our eyes.
The light produced by a nuclear explosion is many times brighter than the sun’s light. If we are looking at the point of detonation, this light can blind us, but the light itself is not ionizing.
Ionizing radiation is electromagnetic radiation that carries more energy than light, enough to strip the electrons off of atoms. Atoms that have had electrons stripped off are called “ions.” Ions are “charged particles.”
The rays of light that have the highest energy, ultra-violet light rays, though usually not ionizing, can damage cells. The “healthy” tans of white people are a sign of that damage.
The electromagnetic radiation that clearly does transmit enough energy to ionize atoms starts at the top end of light energies, beyond the ultra-violet. Radiation with more energy than the ultra-violet becomes x-rays. If it is carrying even more energy, like a a hundred thousand times the energy of light, it becomes gamma rays.
We can’t see or feel or taste or smell x-rays and gamma rays. Ionizing radiation is beyond the reach of our senses. This can make it seem particularly ominous. When I was in junior high this made me think it couldn’t be harmful.
If we get hit by a big enough dose of x-rays or gamma rays, we will, in fact, be killed by it right away or in a few days.
Below that dosage, uncertainties kick in. The ionizing radiation is still likely to harm us but it is harder to say how much, or what kind of harm, or when we will know. The bigger the dose, the worse the odds for us. But odds are just odds. You and I might beat them.