Symbol Pa Atomic radius: pm 161 Fusion: kJ/Mole 12.34
Name Protactinium Ionic radius: pm (+5)78 Boiling point: °C -
Atomic number 91 Electron affinity - Melting point: °C 1572
Atomic weight 231.0 1st  ion potential 5.89 Specific Heat Cap: J/(g K) -
Classification Trans metal Natural form Solid Thermal Cond: W/(cm K) -
Configuration [Rn]5f26d17s2 Crystal structure Tetra Electrical Cond 0.0529
Oxidation states 4,5 Density 14.4 Abundance: mg/kg-crust <0.001
Electronegativity 1.5 Vaporization: kJ/Mole 481.0    
The first isotope, protactinium-234, was discovered in 1913 by Kasimir Fajans and O.H. Göhring.  The long-lived isotope, protactinium-231, was discovered in 1917 independently by Otto Hahn and Lise Meitner. Uses - non known uses