See also: List of individual Rubidium isotopes (and general data sources).
General data
Name of the isotope:Rubidium-81; Rb-81Symbol:81Rb or 8137RbMass number A:81 (= number of nucleons)Atomic number Z:37 (= number of protons)Neutrons N:44Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.1891891891892 (= neutron-proton ratio)Neutron excess (N-Z):7Isotopic mass:80.918994(5) u (atomic weight of Rubidium-81)Nuclide mass:80.8986973 u (calculated nuclear mass without electrons)Mass excess:-75.4566 MeVMass defect:0.751788488 u (per nucleus)Nuclear binding energy:700.28646584 MeV (per nucleus) 8.64551192 MeV (average binding energy per nucleon)Separation energy:SN = 11.353(5) MeV (first neutron) SP = 4.852(5) MeV (first proton)Half-life:4.572(4) hDecay constant λ:4.211305413142 × 10-5 s-1Specific activity α:3.13413115112 × 10+17 Bq g-1 8470624.7327649 Ci g-1Spin and parity: (nuclear angular momentum)3/2-Magnetic dipole moment:μ(μN) = + 2.0591(14)Quadrupole moment Q:+0.398(23) barn (100 fm2)Nuclear g-factor:gl = 1.3727333333333Charge radius:4.2213(51) femtometer fmYear of discovery:1949
Radioactive Decay
Half-life T½ = 4.572(4) h (hours) respectively 1.64592 × 104 seconds s.
The following table shows the atomic nuclei that are isotonic (same neutron number N = 44) and isobaric (same nucleon number A = 81) with Rubidium-81. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.
