Radiation or Radioactivity – Whats the Difference?

Mainstream news stories almost always confuse the very different terms Radiation (like x-rays) and Radioactive (physical materials; fallout), which are significantly distinct things.

Radiation Harm Chart

Radiation (which is emitted From radioactive materials)

      only affects things locally, very locally. While —

Radioactive material (“fallout” in form of dust, water and air)

    can spread through the air, rivers and oceans emitting ionizing radiation all the way around the world.

Here are examples of correct and incorrect usage of the two terms:


The current assumption of the Japanese authorities is that the increased level may have been due to a release of radioactive material from the Fukushima Daiichi nuclear power plant . . .”

    -The International Atomic Energy Agency


“There’s been extensive releases of radiation into the environment and there’s been extensive releases of radiation due to this contaminated water.”

    -PBS News Hour, April 11, 2011, physicist, James Acton, of Carnegie Endowment for International Peace

While perhaps technically arguable as good enough for the general public, this second example is misleading.

The public is seriously concerned about release and spread of radioactive material as dust, in our air and water and soils. It is my experience they are not as concerned about releases of radiation from radioactive materials which only have a local effect.

Radioactive contamination occurs when physical materials emit radioactive materials or gamma rays. Those emitted particles are Helium4 (Alpha), Electrons (Beta), or Neutrons. All can cause ionization in other materials. What is key is that a solid piece of radioactive material does not spread or transfer contamination. Its only when the radioactive piece is turned into dust that it contaminates air, water and soils.

That’s not entirely true because some radioactive materials can transfer radioactivity called Neutron activiation by emitting Neutrons. Practically though, because those materials are common only during fission (in a nuclear reactor while it is operating (or melting down) and at the moment an atomic bomb explodes) these dangerous materials are only extremely rarely released or spilled.

There are many radioactive materials. You really don’t want to breathe or ingest any of them; some you never even want to get close to.

Mrs. Marie Curie was awarded TWO Nobel prizes for her work discovering and developing fundamental understanding of radioactive materials.
Yet Marie Curie died due to ignorance of the harm of those radioactive materials.
This makes me seriously skeptical about people putting radioactive materials in our bodies with essentially no physics training, that means radiologic doctors and technicians.

While some materials like Plutonium and Cesium continue emitting radioactivity for tens of thousands of years, the radioactivity of other materials dissipates to trivial (background levels) in only a few weeks (e.g. most Iodines). Some materials’ radioactivity (some Plutonium isotopes) vanishes in less than a second.

This means it is critical 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 the long lasting Cesium is the dangerous material to keep your eyes on. 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)”


Ionizing radiation directly harms your DNA, enough of it will kill you. Lesser amounts can do serious damage.

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 section is only about Ionizing Radiation.)

The threshold is 318 nanometer wavelength – the energy where Cesium can ionize. (Visible light, Violet, begins with much less energetic photons at about 380 nanometers and extends to Red at about 740 nm.)

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