(7.10-7.13) Background radiation + half-life

What is background radiation?

Radiation that is around us all the time.

• Natural sources

• Man-made sources

List some natural sources of background radiation + their percentage.

Radon gas (50%)

Cosmic rays (10%)

Radioactive material in food and drink (11%)

List some man-made sources of background radiation + their percentage.

Medical sources (13%)

Nuclear waste/fallout/accidents make up the rest.

What is radon gas radiation?

Heavy radioactive elements occur in rocks in the ground.

Uranium decays into radon gas, which is an alpha emitter.

What is cosmic ray radiation?

The sun emits protons every second, some of which enter the Earth’s atmosphere at high speeds.

When they collide with air molecules, gamma radiation is produced.

(Also supernovae and cosmic events)

What is food and drink radiation?

Naturally occurring radioactive elements can get into food and water due to rocks and soil contact.

Not a cause for concern.

What is medical radiation?

Present in X-rays, CT scans, radioactive tracers, radiation theraphy

What is nuclear radiation?

Waste/Fallout/Accidents affect the areas and people nearest.

The fallout can be devastating.

Define the term decay.

The process by which an unstable atomic nucleus loses energy by radiation.

What is the activity of a radioactive source?

The rate at which the unstable nuclei from a source of radiation decays.

What is the unit of activity?

Becquerels (Bq)

1 Bq = I nucleus decaying/second

Why does activity decrease over time?

Each decay reduces the overall number of radioactive particles in the source. Less particles → slower rate of decay.

Define the term half-life.

The take taken for the number of nuclei of a sample of radioactive isotopes to decrease by half.

The time taken for the activity of a sample to fall to half the original level.

How does half-life differ depending on different radioactive isotopes?

Different isotopes have different half-lives. They can vary wildly- fractions of seconds to billions of years.

How can half-life be used to calculate the amount of material remaining?

Half life remains constant, so each half-life that passes causes the amount to decrease by half.

e.g. 2 half lives = ¼ of original material