See also: List of individual Polonium isotopes (and general data sources).
General data
Name of the isotope:Polonium-199m; Po-199mSymbol:199mPo or 199m84PoMass number A:199 (= number of nucleons)Atomic number Z:84 (= number of protons)Neutrons N:115Nucleon pairing (Z - N):even - oddNuclear ratio (N/Z ratio):1.3690476190476 (= neutron-proton ratio)Neutron excess (N-Z):31Excitation energy:310(2) keVIsotopic mass:198.983640(6) u (atomic weight of Polonium-199m)Nuclide mass:198.9375647 u (calculated nuclear mass without electrons)Mass excess:-15.23924 MeVMass defect:1.670128028 u (per nucleus)Nuclear binding energy:1555.71423731 MeV (per nucleus) 7.81765948 MeV (average binding energy per nucleon)Half-life:4.17(5) minDecay constant λ:0.0027703724243003 s-1Specific activity α:8.384394162635 × 10+18 Bq g-1 226605247.63879 Ci g-1Spin and parity: (nuclear angular momentum)(13/2+)Magnetic dipole moment:μ(μN) = -1.005(70)Quadrupole moment Q:+1.40(35) barn (100 fm2)Nuclear g-factor:gl = -0.15461538461538
Radioactive Decay
Half-life T½ = 4.17(5) min (minutes) respectively 2.502 × 102 seconds s.
Decay mode
Daughter
Probability
Decay energy
γ energy (intensity)
α
195Pb
24(1) %
EC/β+
199Bi
73.5(10) %
Iso
199Po
2.5(10) %
Nuclear Isomers
Nuclear isomers or excited states with the activation energy in keV related to the ground state.
The following table shows the atomic nuclei that are isotonic (same neutron number N = 115) and isobaric (same nucleon number A = 199) with Polonium-199m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.
