Beta Decay (AQA GCSE Physics: Combined Science)

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Beta Decay

  • 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

Beta decay, downloadable IGCSE & GCSE Physics revision notes

Beta decay often happens in unstable nuclei that have too many neutrons. The mass number stays the same, but the atomic number increases by one

  • A beta particle is a high-speed electron
  • It has a mass number of 0
    • This is because the electron has a negligible mass, compared to neutrons and protons

  • Therefore, the mass number of the decaying nuclei remains the same
  • Electrons have an atomic number of -1
    • This means that the new nuclei will increase its atomic number by 1 in order to maintain the overall atomic number before and after the decay

  • The following equation shows carbon-14 undergoing beta decay
    • It forms nitrogen-14 and a beta particle
    • Beta particles are written as an electron in this equation

Beta decay equation, downloadable IGCSE & GCSE Physics revision notes

The carbon nucleus emits a beta particle, causing its charge to increase. This means it changes into a new element

Worked example

A nucleus with 11 protons and 13 neutrons undergoes beta decay. It forms magnesium, which has the element symbol Mg.Worked example beta decay, downloadable IGCSE & GCSE Physics revision notesWhich is the correct isotope of magnesium formed during the decay?

ANSWER:  D

Step 1: Calculate the mass number of the original nucleus

    • The mass number is equal to the number of protons plus the number of neutrons
    • The original nucleus has 11 protons and 13 neutrons

11 + 13 = 24

    • The mass number of the original nucleus is 24

Step 2: Calculate the new atomic number

    • During beta decay a neutron changes into a proton and an electron
    • The electron is emitted as a beta particle
    • The neutron has an atomic number of 0 and the proton has an atomic number of 1
    • So the atomic number increases by 1

11 + 1 = 12

    • The new nucleus has an atomic number of 12

Step 3: Calculate the new mass number

    • Protons and neutrons both have a mass number of 1
    • Changing a neutron to a proton will not affect the mass number
    • The new nucleus has a mass number of 24 (the same as before)

Examiner Tip

There is a second form of beta decay during which a proton changes into a neutron. This is called beta-plus decay - you might come across it while revising, but you don't need to know about it for your exam. Only use the information here for your GCSE.

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Ashika

Author: Ashika

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Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.