How a large nucleus splits, how a chain reaction is controlled in a reactor and runs away in a bomb, and how light nuclei join in the stars.
What you will learn
- Describe induced fission and a chain reaction
- Explain how control rods and the moderator work
- Balance a fission equation
- Describe fusion and compare it with fission
Fission
In fission a large, unstable nucleus such as uranium-235 or plutonium-239 splits into two smaller nuclei.
It is rare for this to happen by itself (spontaneous fission); usually the nucleus first absorbs a neutron.
The split gives two smaller nuclei, two or three neutrons, gamma rays and a lot of energy. The fission products all move off fast: the energy starts as kinetic energy.
23592U + 10n → 14156Ba + 9236Kr + 3 10n
- top: 235 + 1 = 236 and 141 + 92 + 3 = 236
- bottom: 92 + 0 = 92 and 56 + 36 + 0 = 92
The rest of this lesson and its 8 practice questions are locked.
In this lesson
- Fission
- Chain reactions
- Fusion
- Try it: Balance a fission equation
8 practice questions, marked as you go; about 20 minutes in all.
Key terms
Fission, Absorbs a neutron, Two or three neutrons, Chain reaction, Nuclear reactor, Control rods, Concrete shield, Moderator, Nuclear weapon, Fusion
In this unit: Atomic structure and radioactivity
The nuclear atom and how its model developed, isotopes, alpha, beta and gamma radiation, nuclear equations, half-life, the hazards and uses of radiation, and fission and fusion.