IGCSEPhysicsOxford AQARevision NotesNuclear PhysicsNuclear FissionNuclear Fission

Nuclear Fission (Oxford AQA IGCSE Physics)

Revision Note

Caroline Carroll

Expertise

Physics Subject Lead

What is Nuclear Fission?

  • There is a lot of energy stored within the nucleus of an atom

    • This energy is in the nuclear energy store

    • This energy can be released in a nuclear reaction such as fission or fusion

  • Nuclear fission is defined as:

The splitting of a large, unstable nucleus into two smaller nuclei

Nuclear Fission Reactions

  • During fission, when a neutron collides with an unstable nucleus, the nucleus splits into two smaller nuclei (called daughter nuclei) as well as two or three neutrons

    • Gamma rays are also emitted

    • Energy is released

  • The products of fission move away very quickly

    • Energy transferred is from the nuclear energy store to the kinetic energy store of the fission products

    • Energy is also transferred to the surroundings by radiation (gamma rays)

  • The energy released in a nuclear fission reaction far exceeds that released in a chemical reaction in which a similar mass of material reacts

Nuclear fission of Uranium-235

A neutron is absorbed by a uranium-235 atom which splits into two daughter nuclei and 2 neutrons, IGCSE & GCSE Physics revision notes
Large nuclei can decay by fission to produce smaller nuclei and neutrons with a lot of kinetic energy

Exam Tip

You need to remember that uranium and plutonium are possible elements for fission, but you do not need to know the specific daughter nuclei that are formed.

Use your knowledge of balancing nuclear equations to work these out.

Worked Example

During a particular spontaneous fission reaction, plutonium-239 splits as shown in the equation below:

Pu presubscript 94 presuperscript 239 space rightwards arrow space Pd presubscript 46 presuperscript 112 space plus space Cd presubscript 48 presuperscript 124 space plus space...

Which answer shows the section missing from this equation?

A

straight n presubscript 0 presuperscript 3

B

straight gamma presubscript 0 presuperscript 0

C

He presubscript 2 presuperscript 4

D

3 space straight n presubscript 0 presuperscript 1

Answer:  D

Step 1: Identify the different mass and atomic numbers

  • Pu (Plutonium) has mass number 239 and atomic number 94

  • Pd (Palladium) has mass number 112 and atomic number 46

  • Cd (Cadmium) has mass number 124 and atomic number 48

Step 2: Calculate the mass and atomic number of the missing section

  • Mass number is equal to the difference between the mass numbers of the reactants and the products

239 – (112 + 124) = 3

  • Atomic number is equal to the difference between the atomic numbers of the reactants and the products

94 – (46 + 48) = 0

  • The answer is therefore not B or C

Step 3: Determine the correct notation

  • Neutrons have a mass number of 1

  • The answer is therefore not A

  • Therefore, this must be three neutrons, which corresponds to D

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    Caroline Carroll

    Author: Caroline Carroll

    Caroline graduated from the University of Nottingham with a degree in Chemistry and Molecular Physics. She spent several years working as an Industrial Chemist in the automotive industry before retraining to teach. Caroline has over 12 years of experience teaching GCSE and A-level chemistry and physics. She is passionate about creating high-quality resources to help students achieve their full potential.