As a nuclear physicist with extensive experience in the field, I can provide an in-depth analysis of the types of uranium used in nuclear weapons. Uranium, a naturally occurring element, has several isotopes, but only a few are relevant to nuclear weapons technology. The primary fissile isotopes used in nuclear weapons are Uranium-235 and Plutonium-239.

Uranium-235, or U-235, is one of the naturally occurring isotopes of uranium, constituting about 0.72% of natural uranium. It is capable of sustaining a chain reaction and is therefore suitable for use in nuclear weapons. The process of enriching natural uranium to increase the concentration of U-235 is a critical step in weapon development. The enrichment is necessary because the natural concentration of U-235 is not sufficient to sustain a chain reaction on its own.

Plutonium-239, on the other hand, is not found naturally in significant quantities. It is a byproduct of nuclear reactors, where it is produced from the neutron capture in U-238. Like U-235, Pu-239 is also fissile and can be used to create a nuclear weapon. The Nagasaki bomb, as you mentioned, was a plutonium-based weapon, demonstrating the effectiveness of this isotope in nuclear warfare.

The production of Pu-239 can be achieved in a breeder reactor, which is designed to generate more fissile material than it consumes. This process is significant because it allows for the creation of a substantial stockpile of plutonium for use in nuclear weapons.

Both U-235 and Pu-239 are considered weapons-grade material due to their ability to undergo fission with the release of a large amount of energy. The choice between using U-235 or Pu-239 in a weapon design can depend on various factors, including the availability of the material, the desired yield of the weapon, and the specific technical requirements of the weapon system.

In summary, while both U-235 and Pu-239 are used in nuclear weapons, the specific isotope chosen depends on the weapon's design and the strategic goals of the state or entity possessing the weapon. The enrichment of natural uranium to extract U-235 and the production of Pu-239 in breeder reactors are both critical processes in the development of nuclear weapons technology.

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Plutonium-239 is a fissionable isotope and can be used to make a nuclear fission bomb similar to that produced with uranium-235. The bomb which was dropped at Nagasaki was a plutonium bomb. Not enough Pu-239 exists in nature to make a major weapons supply, but it is easily produced in breeder reactors.read more >>