Polonium-204m
Properties and data of the isotope 204mPo.
See also: List of individual Polonium isotopes (and general data sources).
General data
Name of the isotope:Polonium-204m; Po-204mSymbol:204mPo or 204m84PoMass number A:204 (= number of nucleons)Atomic number Z:84 (= number of protons)Neutrons N:120Nucleon pairing (Z - N):even - evenNuclear ratio (N/Z ratio):1.4285714285714 (= neutron-proton ratio)Neutron excess (N-Z):36Excitation energy:1639.03(6) keVIsotopic mass:203.980310(11) u (atomic weight of Polonium-204m)Nuclide mass:203.9342347 u (calculated nuclear mass without electrons)Mass excess:-18.34112 MeVMass defect:1.716782608 u (per nucleus)Nuclear binding energy:1599.17269866 MeV (per nucleus)
7.83908186 MeV (average binding energy per nucleon)Half-life:158.6(18) nsDecay constant λ:4370410.9745268 s-1Specific activity α:1.296513817951 × 10+28 Bq g-1
3.504091399868 × 10+17 Ci g-1Spin and parity:
(nuclear angular momentum)8+Magnetic dipole moment:μ(μN) = +7.38(10)Quadrupole moment Q:1.14(5) barn (100 fm2)Nuclear g-factor:gl = 0.9225Year of discovery:1970
Radioactive Decay
Half-life T½ = 158.6(18) ns respectively 1.586 × 10-7 seconds s.
Decay
mode | Daughter | Probability | Decay energy | γ energy
(intensity) |
|---|
| Iso | 204Po | 100 % | | |
Nuclear Isomers
Nuclear isomers or excited states with the activation energy in keV related to the ground state.
| Nuclear Isomer | Excitation Energy | Half-life | Spin |
|---|
| 204Po | | 3.519(12) h | 0+ |
Isotones and Isobars
The following table shows the atomic nuclei that are isotonic (same neutron number N = 120) and isobaric (same nucleon number A = 204) with Polonium-204m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.
| Z | Isotone N = 120 | Isobar A = 204 |
|---|
| 73 | 193Ta | |
| 74 | 194W | |
| 75 | 195Re | |
| 76 | 196Os | |
| 77 | 197Ir | 204Ir |
| 78 | 198Pt | 204Pt |
| 79 | 199Au | 204Au |
| 80 | 200Hg | 204Hg |
| 81 | 201Tl | 204Tl |
| 82 | 202Pb | 204Pb |
| 83 | 203Bi | 204Bi |
| 84 | 204Po | 204Po |
| 85 | 205At | 204At |
| 86 | 206Rn | 204Rn |
| 87 | 207Fr | 204Fr |
| 88 | 208Ra | 204Ra |
| 89 | 209Ac | 204Ac |
| 90 | 210Th | |
Last update: 2025-12-09
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