Radiation vs Radioactivity: What is the Difference?

Back in 2011, a tsunami with a magnitude of nine crashed against the north-east coast of Japan, causing severe damage to the Fukushima-Daiichi nuclear power station and releasing large amounts of radiation into the atmosphere. Over two years later, concerns about how to best go about detecting the levels of radiation still present in the air were still raging on - see the article, Mapping Radiation Data in Japan, for confirmation of these concerns. And though the terms radiation and radioactivity are two separate entities, they are often used interchangeably to describe the situation in Japan, by news sources and, to a lesser extent, by scientific articles. So what exactly is the difference?

What is Radiation?

Radiation generally makes you think of harmful rays coming from nuclear power plants or toxic waste. While these rays are indeed radiation, they do not offer a full definition of the term. This kind of radiation, which has the ability to affect the number of electrons, neutrons and protons in an atom, is called ionising radiation. These have the ability to “charge” atoms, turning them into ions, and are used in power plants, nuclear weapon technology and even in medicine to treat forms of cancer, for example.

However, there are plenty of other kinds of radiation. The waves emitted by your mobile phone are radiation, as is what occurs inside a microwave, what radar signals detect and even what the sun sends down to in the form of sunlight. So although there are harmful kinds of radiation, not all of them are.

What is Radioactivity?

Radioactivity is the nature of a material being compositionally unstable, by having an unstable nucleus. This normally occurs when the number of protons and neutrons in a nucleus do not correspond to each other. When this happens, the substance will become charged as it seeks to naturally address the imbalance by releasing protons or neutrons, thus creating ionised radiation. This radiation, a product of a radioactive substance, has the ability to enter, change and harm all sorts of media, including plants, animals, and, indeed, humans.

Here is a short list of some of the more harmful variants of radiation:

• cesium
• iodine
• strontium-90
• plutonium
• tranuranium elements

These elements have varyingly levels of danger and harm attached to them. All of them can potentially be incredibly damaging, but some have shorter half-lives than others.

What is Radioactive Half-Life?

A half-life is the time it takes for a radioactive substance to lose half of its radioactivity. In iodine, for example, this half-life is relatively short, at only 8 days. After 10 half-lives, a radioactive substance is generally said to be harmless. This means that after 80 days, iodine will cease to be a radioactive threat.

Contrastingly, the half-life of cesium-137 is around 30 years, meaning it will be present in the atmosphere for a much, much longer time and can cause much more serious and long-lasting effect.

In resume, a radioactive substance will always give off radiation … but not all radiation is radioactive.