Mainstream news stories almost always confuse radiation and radioactive (materials), which are significantly different things.
- Radiation means visible light and its cousins: electromagnetic waves including X-rays, gamma rays and radio waves.
- Radioactive means those physical materials which emit ionizing radiation or emit particles that cause ionizing radiation.
- only affects things locally, very locally. While
- can spread in the air and water and emit ionizing radiation all the way around the world.
Here are two examples of correct and wrong usage:
- -The International Atomic Energy Agency
- -PBS News Hour, April 11, 2011, physicist, James Acton, of Carnegie Endowment for International Peace, April 11, 2011
While perhaps technically arguable, this is misleading.
The public is concerned about release and spread of radioactive material – not releases of radiation which only have a local effect.
Ionizing Radiation comes from X-rays, gamma rays and ultraviolet light. It is important because it changes the nature of atoms and molecules by knocking at least one electron out. This gives the atom an electrical charge, and results in a free electron flying around.
Ionizing Radiation does not comes from radio waves, microwaves or visible light because their photons are not strong enough. Their photons are called non-ionizing radiation. (While powerful radio waves can kill you too (think microwave oven), this article is about Ionizing Radiation.) The threshold is 318 nanometer wavelength – the energy where Cesium can ionize. (Visible light, Violet, begins at about 380 nanometers and extends to Red at about 740 nm.)
Radioactive contamination is when physical materials emit radioactive materials or gamma rays. Those emitted particles are electrons (Beta), neutrons, or Helium4 (Alpha). All can cause ionization in other materials.
Ionizing radiation directly harms your DNA, enough of it will kill you. Lesser amounts can do serious damage.
There are many radioactive materials. You really don’t want to breathe or ingest any of them. Some you never even want to get near. (I’m not wild about the idea of people with no physics training, doctors, using radioactive materials in our bodies.)
The radioactivity of some materials dissipates to unimportant in a few weeks (most Iodines), while other materials like Plutonium and Cesium continue emitting radioactivity for years to tens of thousands of years. Some materials’ (some Plutonium isotopes) radioactivity vanishes in less than a second.
It is important to know which specific radioactive materials you are dealing with. Fukoshima has leaked Iodine 131 (half life = 8 days) and Cesium 137 (half-life = 30 years).
Because the Iodine dissipates relatively quickly, the Cesium is the long lasting dangerous material. Cesium emits gamma rays – which damage, and even sort of melt, your DNA.
In Japan 2011, some 25,000 people are known dead from the 9.0 earthquake’s tsunami, but so far no one is yet known to have died from the nuclear plant’s radioactivity. (Curiously, I have not yet read a report of anyone dying directly from the earthquake.)
For more information please see “Understanding Radioactivity Harm Thresholds (in plain English)”