Radiation

Radiation is energy moving through space or matter.

Radiation can be:

• electromagnetic waves like infrared, light, X-rays, and so on
• mechanical waves like sound waves and seismic waves, or
• particles like alpha particles and beta particles (more on those later)

Radiation is emitted from a source, transmitted to a destination, where it can be absorbed.

Here the Sun is the source
and the Earth is the destination

Radiation can also be scattered when hitting particles along the way, as well as reflected, refracted and diffracted (read up on those topics to learn more).

Here we see light (a type of radiation) being scattered by the atmosphere.

Intensity

We can measure radiation intensity at any location as power per area: usually Watts per square meter (W/m²).

As it spreads out on its journey, the intensity gets less.

Inverse Square

When the source is from a point (and not focused, blocked, or absorbed) then the intensity changes as the inverse square of the distance.

Inverse square: when one value decreases as the square of the other value.

Absorbing!

As radiation gets absorbed it loses intensity.

Materials vary in how much they absorb different types of radiation.

When energy is absorbed the material may:

• heat up
• produce electric currents (such as in aerials/antennas)
• help with chemical reactions (like photosynthesis)
• ionize atoms

Ionizing Radiation

High-energy radiation is ionizing, meaning it has enough energy to knock electrons out of atoms.

Losing an electron makes the atom charged and more likely to form new chemical reactions which can be harmful to our cells.

If a cell's DNA is damaged, it can die or change so it grows out of control and forms cancer.

But medicine can use ionizing radiation to help us, such as with X-rays, or as a way to kill cancer cells.

And we live with a small amount of ionizing radiation from the world around us every day.

Ionizing radiation can come from

• Electromagnetic Radiation
• Radioactive atoms

Electromagnetic Radiation

Gamma rays and X-rays and some ultraviolet waves have enough energy to be ionizing.

We also get ionizing radiation from cosmic rays and radioactive materials in the Earth (for example radon gas).

Radioactive Materials

Some atoms have too much energy.

They will randomly decay to a more stable state by sending out radiation.

We say those atoms are radioactive (they can actively emit radiation!)

The radiation emitted has high energy, is ionizing, and can be of 3 types called α, β and γ:

Alpha Particles (α)

Alpha particles have two protons and two neutrons, essentially a helium nucleus.

They are heavy and carry a +2 charge, moving relatively slowly. They are easily stopped by a sheet of paper or a few centimeters of air.

Beta Particles (β)

Beta particles are high-energy electrons (β⁻) or positrons (β⁺).

They have a lot more penetrating power than alpha particles, able to pass through paper but can be stopped by a few millimeters of aluminum or about 1 cm of water.

Gamma rays (γ)

Gamma rays are high frequency electromagnetic waves.

They need thick lead or lots of water to stop them.

Most will go straight through our bodies. But when they hit atoms in our body they can harm us.

Neutron Radiation

There's also neutron radiation, which occurs in nuclear reactions such as thermonuclear explosions or inside nuclear reactors.

Sources

Typical sources of radiation are

• the Sun (many types of radiation, some of which are ionizing)
• X-ray machines
• radioactive materials like uranium and thorium (which are in tiny amounts in the ground, in bricks, stones, soil and concrete, and even in bananas!)
• microwave ovens (non-ionizing)
• and more

Irradiation and Contamination

Irradiation may happen for only a short time, but contamination is inside our body and keeps us irradiated for a long time.

Radiation Doses

We get small amounts of radiation all the time from the world around us. And sometimes a little extra when we have an X-ray.

The health effect of ionizing radiation is measured in Sieverts (Sv).

1 Sv is a very large and dangerous dose, so we tend to talk about:

• microSieverts (µSv), which are one-millionth of a Sv, or
• milliSieverts (mSv) which are one thousand of a Sv

Some typical values:

X-ray of a hand on a computer mouse

Stay safe!