[9] Radioactivity

Proton

Relative mass 1, relative charge +1

Neutron

Relative mass 1, relative charge 0

Electron

Relative mass 1/2000, relative charge -1

Ionised atom

An atom that has lost an electron

Alpha particle

2 protons and 2 neutrons (the nucleus of a helium atom)

Alpha decay effect on nucleus

Mass number decreases by 4 and charge decreases by 2

Beta particle

A high energy (fast moving) electron

Beta decay change

A neutron turns into a proton and emits an electron

Gamma radiation

High frequency electromagnetic radiation

Decay with no change to nucleus

Gamma radiation

Radiation blocked by 3 mm aluminium

Beta radiation (and alpha)

Most ionising radiation

Alpha radiation

Most penetrating radiation

Gamma radiation

Shielding needed for gamma

A few centimetres of lead

Detecting radioactivity

Photographic film

Detecting radioactivity

GM tube (Geiger-Muller counter)

Background radiation source

Cosmic rays

Background radiation source

Radon gas in the air

Half-life

The time taken for half of the radioisotopes to decay

Half-life

The time taken for the activity to halve

Radiation used to sterilise instruments

Gamma radiation because it kills germs

Radiation used to find pipe leaks

Beta radiation because alpha is blocked and gamma passes straight through

Radiation used as a medical tracer

Gamma radiation because it can be detected outside the body

Medical tracer half-life

About 6 hours – long enough for the procedure but short enough to limit exposure

Contamination

Radioactive material is inside or on an object, making it radioactive

Irradiation

Exposure to radiation from an external source without becoming radioactive

Contamination effect

Makes the target radioactive

Irradiation effect

Does not make the target radioactive

Undoing contamination

Can be undone by decontamination

Undoing irradiation

Cannot be undone

Cause of contamination

Transfer of radioactive particles

Cause of irradiation

Exposure to a radioactive source

Preventing contamination

Control of radioactive substances

Preventing irradiation

Shielding

Effects of radiation on cells

Ionisation damages cell membranes and DNA, causing cell death or mutations

Radiation safety measure

Minimise time of exposure

Radiation safety measure

Maximise distance from the source

Radiation safety measure

Use shielding such as lead clothing

Radioactive waste disposal

Buried in sealed drums deep underground and handled remotely after cooling

Smoke detector source

Long half-life alpha emitter

How smoke detectors work

Smoke absorbs alpha particles causing current to drop and trigger alarm

Thickness monitoring source

Long half-life beta emitter

Thickness monitoring method

Beta count changes if sheet thickness changes

Natural source of radiation

Cosmic rays from space

Cosmic ray exposure

Higher at high altitude and during flying

Natural source of radiation

Rocks and soil containing unstable isotopes

Natural source of radiation

Food and drink containing unstable isotopes

Natural source of radiation

Radon gas released from rocks into the air

Radon gas levels

Higher in some regions than others

Artificial source of radiation

Fuel for nuclear power stations

Artificial source of radiation

Fallout from nuclear weapons testing and nuclear disasters

Artificial source of radiation

Medical equipment

PET scan

Positron Emission Tomography

PET radioactive source

Beta plus (positron) emitter

Beta plus decay

A proton turns into a neutron and emits a positron

Positron annihilation

A positron meets an electron and they convert into energy

Result of positron annihilation

Two gamma rays emitted

PET detection method

Detection of two gamma rays

PET image formation

Gamma ray angle and timing differences allow 3D position to be found

Becquerel (Bq)

Unit of radioactivity

1 Bq

One nuclear decay per second

Henri Becquerel

Scientist who discovered radioactivity in uranium