protactinium -
A chemical element symbol Pa with atomic number 91.
Wikipedia
Protactinium is a chemical element with the symbol Pa and atomic number 91. Its longest-lived and most abundant naturally occurring isotope by far, Pa-231, is a decay product of uranium-235 (U-235), and it has a half-life of 32,760 years. Much smaller trace amounts of the short-lived metastable isotope Pa-234m occur as decay products of uranium-238 (U-238).
OmegaWiki Dictionary
Ω
protactinium Chemical element with symbol Pa and atomic number 91. It is a silvery actinide.
