(n)a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead, Syn.protoactinium, atomic number 91, Pa
The Collaborative International Dictionary of English (GCIDE) v.0.53Collaborative International Dictionary (GCIDE)
. The radioactive chemical element, of atomic number 91; Atomic symbol Pa; at. wt. of longest-lived isotope, 231 (T1/2 = 32, 500 yrs.) Also called brevium, Uranium X2 and UX2. [ PJC ]