Atomic and nuclear properties of materials:
Positronium (atom with e+ as nucleus)
QuantityValueUnitsValueUnits
Atomic number 1 n n n
Mass* +/- 1.097 526 752
+/- 0.000 000 005
10-3 u +/- 1.021 991 03
+/- 0.000 000 09
MeV
Mean lifetime
(annihilation)
Singlet: 125 ps Doublet: 140 ns
* Ground state binding energy = Ry/2.

Is it reasonable to consider Ps as a chemical element?