E4 Fission

Fission (a-> b+c)

E4.1 Fission

Splitting of large unstable nucleus into 2 smaller nuclei + neutrons and gamma rays after neutron collides with it.

Eg. n + ²³⁵U → ²³⁶U → 2 daughter elements + gamma + neutrons

The products move away very quickly as energy is transferred from nuclear potential energy → kinetic energy → heat.

E4.2 Spontaneous fission vs induced

rare, doesnt happen often without energy input…

induced; absorb neutron so stable-ish uranium235 → uranium236 (unstable and splits easily)

E4.3 Energy released in fission

Daughters have higher binding energy per nucleon. Energy released.

Nuclear fission is fuel source with higest energy density of any fuels..

density = ^{E density}/_{specific E} . nr of atoms: ^{mass(g) x N_a}/_{molar mass}

E4.4 Neutrons in fission

neutrons in induced fission: thermal neutrons: low E and speed; too much E would rebound form the Uranium nucleus. Each produced/ new neutron can start a new fission reaction, creating further excess neutrons: chain reaction.

E4.5 Critical mass

Nuclear reactions are self-sustaining yet controlled; using precise amount of uranium fuel; critical mass (maintain steady chain react)

use less: would stop: subcritical, use more: explosion, supercritical

E4.6 Nuclear reactor

Use chain reaction to keep reactor running. Nr & E of free neutrons controlled to have required rate of energy production.