Baryon Updated 2025-07-16
The most important examples by far are the proton and the neutron.
Baryon vs meson vs lepton Updated 2025-07-16
"Barys" means "heavy" in Greek, because protons and neutrons was what made most of the mass of known ordinary matter, as opposed notably to electrons.
Baryons can be contrasted with:
Chicago Pile-1 Updated 2025-07-16
Video 1.
Getting funding for the Chicago Pile Edward Teller interview by Web of Stories (1996)
Source.
Video 2.
German graphite from The Genius Behind the Bomb (1992)
Source. Graphite was expensive because it had to be boron-free, since boron absorbs neutrons. But a boron process was the main way to make graphite. This type of pure graphite is known as nuclear graphite.
Direct energy conversion Created 2024-08-02 Updated 2025-07-16
Neutron cross section Created 2024-08-14 Updated 2025-07-16
Figure 1.
Uranium-235 neutron cross section as a function of neutron energy
. Source.
Figure 2.
Neutron cross section for various uranium isotopes
. Source.
Figure 3.
Neutron cross section of two isotopes of Boron as a function of neutron speed
. Source.
Neutron temperature Updated 2025-07-16
The speed of neutrons greatly influences how well they are absorbed by different isotopes.
Nuclear force Updated 2025-07-16
Side effect of the strong force that in addition to binding individual protons and neutrons as units, also binds different protons and neutrons to one another.
Plutonium-239 Created 2024-08-14 Updated 2025-07-16
This is the isotope that is produced for nuclear weapons by irradiating Uranium-238 with a neutron.
Plutonium-240 is a contaminant.
Plutonium-240 Created 2024-08-14 Updated 2025-07-16
This isotope shows up as an inevitable contaminant in Plutonium-239 for nuclear weapons, because it emits neutrons too fast and makes it harder to assemble the critical mass without fizzle.
Wikipedia explains that Pu-240 is formed by Pu-239 Neutron capture:
About 62% to 73% of the time when 239Pu captures a neutron, it undergoes fission; the remainder of the time, it forms 240Pu.
so its presence is inevitable.
Thermal neutron Created 2024-08-14 Updated 2025-07-16
These are neutrons that have reached the thermal equilibrium according to the Maxwell-Boltzmann distribution after having bounced around many times without undergoing neutron capture.
Good fissile material is material that is able to absorb thermal neutrons and continue the reaction, because that's the type of neutron you end up getting the most of.
Weak interaction Updated 2025-07-16
Explains beta decay. TODO why/how.
Maybe a good view of why this force was needed given beta decay experiments is: in beta decay, a neutron is getting split up into an electron and a proton. Therefore, those charges must be contained inside the neutron somehow to start with. But then what could possibly make a positive and a negative particle separate?
www.thestargarden.co.uk/Weak-nuclear-force.html gives a quick and dirty:
Beta decay could not be explained by the strong nuclear force, the force that's responsible for holding the atomic nucleus together, because this force doesn't affect electrons. It couldn't be explained by the electromagnetic force, because this does not affect neutrons, and the force of gravity is far too weak to be responsible. Since this new atomic force was not as strong as the strong nuclear force, it was dubbed the weak nuclear force.
Also interesting:
While the photon 'carries' charge, and therefore mediates the electromagnetic force, the Z and W bosons are said to carry a property known as 'weak isospin'. W bosons mediate the weak force when particles with charge are involved, and Z bosons mediate the weak force when neutral particles are involved.
Video 1.
Weak Nuclear Force and Standard Model of particle physics by Physics Videos by Eugene Khutoryansky (2018)
Source. Some decent visualizations of the field lines.