WordNet
n. a highly fissionable isotope of plutonium that is used in atomic weapons and as a reactor fuel; produced by irradiating uranium 238 with slow electrons
Usage examples of "plutonium 239".
The central aiming point of the explosives and the metallic projectiles was a ten kilogram (22 pound) mass of radioactive plutonium 239.
The plutonium 239 mass also included a small but troublesome quantity of plutonium 240, which was even less stable and prone to pre-ignition.
One can assume that a mixture of Plutonium 239 (highly refined hence relatively low radioactivity emission on detonation), Lithium 6 Deuteride Tritide, Tritium, and possibly Beryllium and Uranium 238 (NOT 235) would be involved as a series of lenses in a Bi-Conical shape.
President: You asked that I review both the Portland, Oregon, FBI seizure of 265 grams of highly-enriched Plutonium 239 last month and the 1994 German seizures of similar materials alleged to have come from Russia.
That particular device consisted of one kilogram of Plutonium 239 encased in a one-inch-thick sphere or tamper of Uranium 238.