n.
Radioactive (see radioactivity ) metallic chemical element , chemical symbol Pu, atomic number 94.
A member of the actinide series of transition element s, it is the most important transuranium element because of its use in certain types of nuclear reactors (see nuclear power ) and in nuclear weapon s. It is found in nature only in traces produced by natural neutron irradiation in uranium ores. It is produced artificially by neutron irradiation of uranium-238. Plutonium is a silvery metal that tarnishes in air; it is warm because of energy released in alpha decay . Its isotope s, all radioactive, are highly toxic radiological poisons (see radiation injury ) because they give off alpha particles and are specifically absorbed by bone marrow.