Explain how Nuclear Fission can lead to a chain reaction - 3 marks

When uranium-235 absorbs a neutron, it becomes unstable and splits into two daughter nuclei, barium and krypton, releasing three free neutrons. These free neutrons can then induce further fission in other uranium-235 nuclei, perpetuating a chain reaction.

Initial Fission Event: When a uranium-235 nucleus absorbs a neutron, it becomes unstable and splits into two smaller nuclei (e.g., barium and krypton), releasing energy and additional neutrons.

Release of Neutrons: The initial fission event typically releases 2-3 free neutrons. These neutrons can collide with other uranium-235 nuclei.

Sustaining the Reaction: Each of these newly collided uranium-235 nuclei can undergo fission, releasing more neutrons. If at least one of these neutrons causes another fission event, the process continues, creating a self-sustaining chain reaction.

This chain reaction can release a significant amount of energy, which is harnessed in nuclear reactors or leads to explosive yields in nuclear weapons.