Atomic number: 91

Symbol: Pa

Category: actinide 

Density at 25°C: solid: density: 15.37 g·cm−3

This is a very rare and highly radioactive element and only found in trace amounts in uranium ore. It currently has no practical uses outside of pure scientific research. 

Use, natural applications or common combinations: 

  • by product of thorium reactors

Basic characteristics:

  • Standard atomic weight: 231.035 88(2)
  • Melting point: 1568 °C
  • Boiling point:  4027 °C (uncertain)
  • Radioactivity: all radioactive
    • 231Pa with a half-life of 32,760 years emitting alpha particles