Average atomic weight: 138.90547(7) u
| Isotope | Fraction | Atomic weight/u |
| 138 | 0.0008881(71) | 137.9071149(37) |
| 139 | 0.9991119(71) | 138.9063563(24) |
Atomic weights and isotopic compositions were obtained from NIST Database 144
The Atomic Line List does not contain any data for this element
(Atomic Line List v3.00b5)
