Protactinium

Protactinium (symbol Pa) is a chemical element, atomic number 91 on the periodic table.

Characteristics and history
Protactinium, in its most stable form, has an atomic mass of 231. Protactinium was discovered by Humans on Earth's European continent for the first time by scientists working in England and Germany in the year 1917. This element is part of the actinide series of heavy elements.