Alpha, Beta & Gamma Radiation (Oxford AQA IGCSE Combined Science Double Award)

Alpha, Beta & Gamma Radiation

• When an unstable nucleus decays, it emits radiation

• Substances that emit radiation are said to be radioactive

• There are different types of radiation that can be emitted:

  • Alpha (α) particles

  • Beta (β^-) particles

  • Gamma (γ) waves

  • Neutrons

• These changes are spontaneous and random in direction

  • There is an equal probability of any nucleus decaying

  • It cannot be known which particular nucleus will decay next

  • It cannot be known at what time a particular nucleus will decay

  • The rate of decay is unaffected by the surrounding conditions, or chemical and physical processes

  • It is only possible to estimate the probability of a nucleus decaying in a given time interval

Composition of Alpha, Beta & Gamma Radiation

Alpha particles

• The symbol for alpha particles is α

• An alpha particle is a helium nucleus

  • It is made of 2 protons and 2 neutrons

• Alpha particles have a charge of +2

  • This means they can be affected by an electric field

• During alpha decay, an alpha particle is emitted from an unstable nucleus

• A completely new element is formed in the process because the atomic number changes

 An unstable nuclei decaying by alpha radiation

Beta particles

• The symbol for beta is β

• A beta particle is a high-speed electron

• Beta particles have a charge of -1

  • This means they can be affected by an electric field

• During beta decay, a neutron changes into a proton and an electron

  • The electron is emitted and the proton remains in the nuclei

• A completely new element is formed because the atomic number changes

 An unstable nuclei decaying by beta radiation

Gamma radiation

• The symbol for gamma is γ

• Gamma radiation is electromagnetic radiation

  • They have the highest energy of the different types of electromagnetic radiation

• Gamma radiation has no mass or charge

• During gamma decay, gamma radiation is emitted from an unstable nucleus

• The process that makes the nucleus less energetic but does not change its structure

  • The atomic number and mass number remain the same

An unstable nuclei decaying by gamma radiation

Neutrons

• The symbol for a neutron is n

• Neutrons are one of the two particles found in the nucleus of atoms

• Neutrons are neutral, they have no charge

Summary of the composition of different types of radiation

Properties of Alpha, Beta & Gamma Radiation

Extension Tier only

• The properties of alpha, beta and gamma are given in this table, and then described in more detail below

Different Properties of Nuclear Radiation

• The trend down the table shows:

  • The range increases

  • Penetrating power increases

  • Ionisation decreases

Penetrating power

• Alpha, beta and gamma have different properties

• They penetrate materials in different ways

  • This means they can pass through certain materials and therefore can be stopped by certain materials

Penetrating power of alpha, beta & gamma

• Alpha is stopped by paper, whereas beta and gamma pass through it

• Beta is stopped by a few millimetres of aluminium

• Gamma can pass through aluminium

  • Gamma rays are only partially stopped by thick lead

Ionising power

• All nuclear radiation is capable of ionising atoms that it hits

• When an atom is ionised, the number of electrons it has changes

• This gives it a non-zero charge

Ionisation of an atom

• Alpha radiation is the most ionising form of nuclear radiation

  • This is because alpha particles have a charge of +2

• Gamma radiation is the least ionising form of nuclear radiation

Range in air

• The more ionising a form of radiation is, the sooner it will interact with the air it is moving through

• Strongly ionising radiation has the shortest range in air

  • Alpha only travels a few centimetres in air

  • Beta has a range of a few tens of centimetres

  • Gamma is not absorbed by air and so has an infinite range, although it does get less intense with distance