Large nucleus can split into two nuclei {fission, physics}| {nuclear fission}. Fission releases million times more energy per mass than burning. In nuclear reactions, neutrons collide with uranium or plutonium nuclei to cause fission.
Neutron can decay into proton, electron, and anti-neutrino {beta decay}| {beta radiation}. Beta decay causes nucleus to lose neutron and gain proton.
Nuclear reactors {breeder reactor} can use neutrons from fission to form plutonium from uranium.
Electron and positron collision {electron-positron collision} makes two real photons, positive pion and negative pion, proton and anti-proton, or virtual photon that becomes rho vector meson that makes two pions. Process must make two particles to conserve energy and momentum.
High-energy photon and atomic nucleus can collide to make electron and positron {pair production}. Protons and neutrons absorb photons 200 times less than hyperons.
Particle decays {decay, particle} {particle decay}| always make two particles, to conserve energy and momentum.
Proton and proton collisions {proton-proton collision} at high energies make larger subatomic particles. Scattering happens if both protons have same spin, but not if protons have opposite spins.
Particles can collide and rebound {scattering, collision}|.
path
In gas, particles go average distance, through mean free path, before they hit another particle.
elastic
Both particles can collide, bounce off, and remain intact, with no new particles {elastic scattering}.
inelastic
Both particles can collide to make new particles {inelastic scattering}. Created particles go off in pairs in jets perpendicular to colliding-particle paths. Increased amplitude at collision resonance energy indicates particle creation at that mass.
Small particles scatter through wider angles than larger particles, because cross-sectional area is less. Cross-sectional area increases with energy.
particle size
Particles have minimum diameter at 70 to 300 MeV. Particles grow rapidly in diameter up to at least 1500 MeV. At collision energy 2 GeV, particles reach maximum diameter.
Crystals exposed to radioactivity trap electrons in crystal faults. By heating material, luminescence {thermo-luminescence} measures number trapped. Thermo-luminescence can date from recent times to hundreds of thousands of years ago. Electron-spin resonance also measures number trapped.
Two small nuclei can merge into one nucleus {fusion, physics} {nuclear fusion}|. Fusion releases million times more energy per mass than burning.
products
Nuclear fusion makes all atoms up to and including iron.
efficiency
Nuclear hydrogen fusion to helium makes 0.007 of mass into energy, so efficiency is 0.007. Other fusions make 0.017 of mass into energy. If efficiency is less, universe has no or less helium and heavy atoms. If efficiency is more, universe has more helium and heavy atoms, but no hydrogen. Carbon production also depends on ratio, because it involves resonance energy.
Main fusion reaction {proton-proton cycle} unites two protons. In stars, hydrogen fusion to helium requires 10^6 K. Two protons change to deuterium and proton. These two nuclei combine to make helium 3. Two helium 3 make helium 4 and two protons.
The second-most-important fusion reaction {carbon-nitrogen cycle} makes helium starting from protons and carbon. Carbon acts like catalyst to make lithium, beryllium, and boron, which combine or decay to helium. Carbon-nitrogen cycle is not chain reaction.
Reactions {chain reaction, fusion}| that have proton reactants and make protons can be self-sustaining. Chain reaction continues until limiting reactant amount becomes zero or system disrupts physically.
Minimum mass {critical mass} starts chain reactions. Below minimum mass, too many proton initiators do not collide and escape to outside.
Absorbing protons {damping} slows fusion reactions. In nuclear reactors, metal rods absorb proton initiators to slow reaction.
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Date Modified: 2022.0225