Nuclear Fission Diagrams

Nuclear Fission Process

Nuclear fission is the splitting of a large, unstable atomic nucleus into two smaller nuclei, called fission products. This process releases a significant amount of energy.

The fission process begins when a neutron is absorbed by a large nucleus, such as uranium-235 or plutonium-239. This absorption makes the nucleus unstable, causing it to split.

When the nucleus splits, it produces:

• Two smaller nuclei (fission products), which are usually radioactive
• Several free neutrons (usually 2 or 3)
• A large amount of energy released mainly as kinetic energy of the fragments

The released neutrons can then be absorbed by other nearby nuclei, potentially causing further fission events.

For instance, when a uranium-235 nucleus absorbs a neutron, it becomes unstable uranium-236, which then splits into two smaller nuclei (like barium-141 and krypton-92), releases 3 neutrons and energy. Uranium-236 is a highly unstable intermediate nucleus that exists only briefly before splitting.

This energy is harnessed in nuclear power stations to generate electricity.

Example: Typically, 2 or 3 neutrons are released per fission event. If 3 neutrons are released, and 2 cause further fission, the remaining neutron may be absorbed or lost, helping control the reaction.

Fission Chain Reaction Diagram

A fission chain reaction occurs when the neutrons released by one fission event cause further fission in other nuclei, sustaining the process.

In a nuclear reactor, this chain reaction is carefully controlled to maintain a steady release of energy:

• Neutrons released from fission collide with other uranium or plutonium nuclei, causing more fission.
• Control rods, made from materials like boron or cadmium, absorb excess neutrons to prevent the reaction from accelerating uncontrollably.
• The diagram of a chain reaction shows neutron paths as arrows, nuclei as circles or spheres, and control rods inserted to absorb some neutrons.

This controlled chain reaction allows nuclear power stations to produce a steady amount of energy safely.

Diagram Components

A typical nuclear fission diagram includes the following key components:

• Uranium or Plutonium nucleus: Usually represented as a large circle or oval labelled with the element symbol and mass number (e.g., U-235).
• Incoming neutron: Shown as a small dot or arrow pointing towards the nucleus, indicating the neutron that triggers fission.
• Fission fragments: Two smaller nuclei produced after the split, often labelled with their element symbols and mass numbers (e.g., Ba-141 and Kr-92).
• Released neutrons: Usually 2 or 3 small dots or arrows moving away from the fission fragments, representing neutrons emitted during fission.
• Neutron paths: Arrows showing the directions of neutrons, especially those that may cause further fission events.
• Control rods (if shown): Bars inserted into the reactor core to absorb excess neutrons and control the chain reaction.

These diagrams help visualise how a neutron initiates fission, how the nucleus splits, and how neutrons propagate the chain reaction.

For example, a diagram might show a neutron hitting a uranium-235 nucleus, which then splits into two smaller nuclei and releases three neutrons travelling in different directions, with some neutrons absorbed by control rods.

Understanding these diagrams is essential for grasping how nuclear reactors operate and how fission energy is controlled.

Example: In a diagram, if a neutron hits a uranium-235 nucleus and causes it to split into barium-141 and krypton-92, releasing 3 neutrons, these neutrons can then be shown moving towards other uranium nuclei to continue the reaction.