Actinide

Actinide is a term used in chemistry for fifteen metallic elements of the periodic table from atomic number 89 to atomic number 103. The series derives its name from the first element in the series, actinium, having atomic number 89.

Their atomic names, numbers and symbols are:
Actin­ium - 89 -Ac, Thor­ium - 90 - Th, Protac­tinium - 91 - Pa, Ura­nium - 92 - U, Neptu­nium - 93 - Np,
Pluto­nium - 94 - Pu, Ameri­cium - 95 - Am, Curium - 96 - Cm, Berkel­ium - 97 - Bk, Califor­nium - 98 - Cf, Einstei­nium - 99 - Es, Fer­mium - 100 - Fm, Mende­levium - 101 - Md, Nobel­ium - 102 - No, and Lawren­cium - 103 - Lr.

These are all radioactive elements and extremely unstable. Uranium and thorium are found in nature in substantial quantities, and plutonium is also found in little quantities. The radioactive decay of uranium produces transient amounts of actinium and protactinium, and atoms of neptunium, americium, curium, berkelium and californium are occasionally produced from transmutation reactions in uranium ores. The other actinides are purely synthetic elements.