Alpha particles have low penetration depth Created 2024-08-14 Updated 2025-07-16
They are stopped by:
  • by a few centimeters of air
  • a sheet of paper
  • the skin
Therefore, alpha emitters are not too dangerous unless ingested.
Gun-type fission weapons don't work with plutonium Created 2024-08-14 Updated 2025-07-16
Gun-type fission weapons don't work with Plutonium-239 because of the presence of Plutonium-240 as an impurity which leads to fizzle.
Gamma spectroscopy Created 2024-08-14 Updated 2025-07-16
Figure 1.
Gamma spectroscopy of a Uranium ore
. Source. Several points of the Uranium 238 decay chain are clearly visible.
Breeder reactor Created 2024-08-14 Updated 2025-07-16
A nuclear reactor made to produce specific isotopes rather than just consume fissile material to produce electrical power. The most notably application being to produce Plutonium-239 for nuclear weapons from Uranium-238 being irradiated from Uranium-235-created fission.
Weapon grade Plutonium is cheaper than weapon grade Uranium Created 2024-08-14 Updated 2025-07-16
Because you can generate plutonium-239 from uranium-238 in a breeder reactor, and then separate the plutonium-239 from the Uranium simply by using chemistry methods because you've created an element with different valence electrons.
Isn't it somewhat funny that it is easier to purify a synthetic element than a naturally occurring one?
Thorium-232 Created 2024-08-14 Updated 2025-07-16
GPHS-RTG Created 2024-08-14 Updated 2025-07-16
Figure 1.
GPHS-RTG diagram
. Source.
Figure 2.
Cassini probe's RTG before installation
. Source.
Polonium-209 Created 2024-08-14 Updated 2025-07-16
Polonium-208 Created 2024-08-14 Updated 2025-07-16
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.
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-238 Created 2024-08-14 Updated 2025-07-16
Strong alpha emitter. Can be used as an atomic battery.
Figure 1.
Plutonium-238-oxide pellet glowing under its own heat
. Source. Unlike for nuclear applications, we don't need the pure metal, so the oxide 238PuO2 is used instead as it is more chemically stable.
S-50 liquid thermal diffusion plant Created 2024-08-14 Updated 2025-07-16
K-25 Created 2024-08-14 Updated 2025-07-16
Y-12 electromagnetic separation plant Created 2024-08-14 Updated 2025-07-16
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.
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.

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