| Quantity | Value | Units | 
 
Value | Units | 
 
|  Atomic number | 
  
  86 | 
  | 
  |   | 
 
 
|  Atomic mass | 
  
[222.01758(2)] | 
g mole-1 | 
  |   | 
 
 
|  Specific gravity 
(20° C, 1 atm) | 
  
      9.066E-03 | 
g cm-3 | 
  |   | 
 
 
|  Mean excitation energy | 
  
 794.0 | 
eV | 
  |   | 
 
 
|  Minimum ionization | 
  
  1.116 | 
MeV g-1cm2 | 
  
      1.011E-02 | 
MeV cm-1 | 
 
 
| Nuclear collision length | 
  
  116.3 | 
g cm-2 | 
  
      1.283E+04
 | cm | 
 
 
| Nuclear interaction length | 
  
  204.3 | 
g cm-2 | 
  
      2.253E+04
 | cm | 
 
 
|  Pion collision length | 
  
  139.4 | 
g cm-2 | 
  
      1.537E+04
 | cm | 
 
 
|  Pion interaction length | 
  
  230.7 | 
g cm-2 | 
  
      2.544E+04
 | cm | 
 
 
| Radiation length | 
  
   6.28
 | g cm-2 | 
  
    693.2      
 | cm | 
 
 
| Critical energy | 
  
   7.71 | 
MeV (for e-) | 
  
   7.43
 | MeV (for e+) | 
 
 
| Molière radius | 
  
  17.30 | 
g cm-2 | 
  
    1908.      
 | cm | 
 
 
|  Plasma energy ℏωp | 
  
  1.71 | 
eV | 
  |   | 
 
 
| Muon critical energy | 
  
   160. | 
GeV | 
  |   | 
 
 
| Melting point | 
  
    202.1       | 
K | 
  
   -71.00      
 | C | 
 
 
| Boiling point @ 1 atm | 
  
    211.4      
 | K | 
  
   -61.70      
 | C | 
 
 
For muons,