Atomic and nuclear properties of positronium (Ps):
Positronium (Z = 1 atom with e+ as nucleus)
Quantity | Value | Units | Value | Units
| Atomic number
|
1
| n
| n
| n
| Mass*
|
1.097 526 752 (5)
| 10-3 u
|
1.021 991 03 (9)
| MeV
| Mean lifetime (annihilation) |
Singlet (p-Ps): 125
(Predominately Ps→2γ) |
ps |
Triplet (o-Ps): 142.05 ± 0.02
(Predominately Ps→3γ) | ns
|
* Ground state binding energy = Ry/2.
Is it reasonable to consider Ps as a chemical element?
-
It is bound electronically. If we consider atoms as having orbital
electrons,
then the positron plays the role of nucleus.
-
It has a rich chemistry, as Google searches on "positronium halides,"
"positronium compounds," and other strings show. There are international
conferences on positronium chemistry.
-
In other exotic atoms such as muonium, pionium, and kaonium, the bound
muon or meson plays the role of an orbital electron instead of being the
nucleus. Although e−π+ and other such
atoms might equally well be regarded as elements, as would atoms with
hypernuclei, these contain unstable particles.
An isolated positron is presumably as stable as an electron.
-
One serious objection is that the positronium "nucleus" has non-zero
lepton
number.
(e−π+ and atoms with hypernuclei have nuclei with lepton number
zero, as do "normal" nuclei.)
- We are physicists, not chemists.
|