Positronium

{
  "id": "MLC-T-CHM-009299",
  "term": "Positronium",
  "field": "Chemistry",
  "definition": "An exotic atom consisting of an electron and its antiparticle, the positron, bound together into an atomic system. This system is chemically analogous to a hydrogen atom, where the proton is replaced by a positron, and it is highly unstable due to particle-antiparticle annihilation. It exists in two ground states: parapositronium, with a lifetime of about 125 picoseconds, and orthopositronium, with a much longer lifetime of about 142 nanoseconds in a vacuum.",
  "subject": "Physical and Biophysical Chemistry",
  "see_also": [
    "anti",
    "positron"
  ],
  "references": [
    "Green Book, 2nd ed., p. 93 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf)"
  ],
  "url": "https://mlchart.com/terminology/chemistry/positronium/"
}