Protactinium

1.

The radioactive chemical element, of atomic number 91; Atomic symbol Pa; at. wt. of longest-lived isotope, 231 (T½ = 32,500 yrs.) Also called brevium, Uranium X2 and UX2.

Noun

1.

protactinium - a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead Synonyms: atomic number 91, protoactinium, Pa

atomic number 91, metal, metallic element, Pa, protoactinium