Radioactivity

What is a radioactive substance?

A substance containing an unstable nuclei that becomes stable by emitting radiation

How is radioactivity measured?

In bequerels (Bq)

↳ 1Bq = 1 decay per second

How can radioactivity be described?

Random- you don't know:

↳ Which atom will decay next

↳ When any particular atom will decay

Define half-life

The time it takes for half the nuclei in a sample to decay

How can an unstable nucleus decay?

By emitting :

• Alpha particles

• Beta particles

• A gamma ray

• A single neutron

What happens when an atom emits an alpha particle?

• Mass number decreases by 4

• Atomic number decreases by 2

↳ can be written as a helium atom

What happens when an atom emits a beta particle?

A neutron will turn into a proton an emit an electron

↳ Atomic number increases by 1

↳ Mass number stays the same

What happens when an atom emits a gamma ray?

After an atom emits an alpha or beta particle, the nucleus will be too ‘hot'

↳ It cools by emitting infrared radiation which is an electromagnetic wave so the atomic and mass number both stays the same

What happens if an atom emits a neutron?

• Mass number decreases by 1

• Atomic number stays the same

What are the properties of alpha radiation?

• Penetration power

  ↳ Stopped by paper

• Range in air

  ↳ Few cm of air

• Ionising power

  ↳ High

What are the properties of beta radiatiion?

• Penetrating power

  ↳ stopped by a few mm of aluminium

• Ionising power

  ↳ Low

• Range in air

  ↳ 1 metre

What are the properties of gamma radiation?

• Penetrating power

  ↳ Thick lead/concrete

• Ionising power

  ↳ Very low

• Range in air

  ↳ Not stopped by air

Define ionising power

The ability to carge an uncharged particle

↳ Higher the penetrating power → lower the ionising power

How can radioactive decay be detected?

By using a geiger-muller tube

↳ Radiation ionises the gas inside resulting in charged particles to move across the chamber and get counted as charges

What is contamination

When a radioactive material is in contact with a person so they are constantly being irradiated

What is irradiation?

When a person is being exposed to a radioactive material

How can you prevent irradiation?

• Keep radioactive sources in a lead lined box

• Wear face masks/protective clothing

• handle materials with tongs

How are radioactive sources used in medicine?

• Treating tumours

  ↳ Gamma radiation in a narrow beam is fired at cancerous tumours in all directions to destroy them

• To diagnose patients

  ↳ Used in radioactive tracers which can trace the flow of substances through an organ → detecting a blocked kidney

Define nuclear fission. What happens?

The splitting of a large and unstable nucleus

↳ The nucleus is split in 2 smaller nuclei and emits 2 or 3 neutrons and gamma rays. Energy is also released

What is a chain reaction in terms of nuclear fission

When the neutrons emitted from nuclear fission go on to collide with other uranium nuclei to cause further fission reactions

What is nuclear fusion?

The joining of 2 light nuclei to form a heavier nucleus

↳ Some of the mass may be converted into the energy of radiation

Why are we constantly exposed to background radiation?

Background radiation comes from:

• Rocks and cosmic rays

• Fallout from nuclear weapons testing and accident

Your dose of background radiation depends on your occupation and location