Fission of U-235 (spec 7.17 - 7.19)
Neutron in β split β energy + neutrons out.
Three nuclear processes release energy:
- Fission β a large nucleus splits.
- Fusion β small nuclei join.
- Radioactive decay β Ξ±, Ξ², Ξ³ emission from unstable nuclei (covered in the Radioactivity subtopic).
U-235 fission step-by-step (spec 7.18, 7.19).
- A SLOW (thermal) neutron strikes a U-235 nucleus.
- The neutron is absorbed β temporary U-236 nucleus, which is highly unstable.
- The unstable nucleus SPLITS into TWO daughter nuclei (commonly Ba-141 + Kr-92, or Sr-90 + Xe-143).
- A small number (typically 2 or 3) of fast neutrons are released.
- Most of the energy released appears as KINETIC ENERGY of the daughter nuclei and neutrons. This kinetic energy is rapidly transferred to thermal energy of the reactor fuel and coolant.
The daughter nuclei are themselves RADIOACTIVE (spec 7.19) β they continue to emit radiation for years, which is why spent nuclear fuel is dangerous and must be carefully stored.
Balancing the equation. Nucleon AND proton numbers are conserved.
Example:
- Nucleons: . β
- Protons: . β
- Slow neutron β U-235 β 2 daughters + 2-3 neutrons + energy.
- Daughters are RADIOACTIVE.
- Most energy = kinetic energy of products β heat.