 Plutonium-239

This is the isotope that is produced for nuclear weapons by irradiating Uranium-238 with a neutron.

Plutonium-240 is a contaminant.

Plutonium-239 (Pu-239) is a man-made isotope of plutonium, which is a radioactive element. It is notable for its use in nuclear reactors and nuclear weapons. Here are some key points about Pu-239: 1. **Isotope**: Plutonium has several isotopes, and Pu-239 is one of the most significant due to its properties.