Bromine-81
Properties and data of the isotope 81Br.
Bromine-81 is a stable isotope of the chemical element bromine, which has 46 neutrons in its atomic nucleus in addition to the element-specific 35 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 81. Br-81 accounts for 49,45% of natural terrestrial bromine deposits.
The first mass spectrometric detection and thus the discovery of bromine-81 was reported in 1920 [1].
See also: List of individual Bromine isotopes (and general data sources).
General data
Name of the isotope:Bromine-81; Br-81Symbol:81Br or 8135BrMass number A:81 (= number of nucleons)Atomic number Z:35 (= number of protons)Neutrons N:46Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.3142857142857 (= neutron-proton ratio)Neutron excess (N-Z):11Isotopic mass:80.9162882(10) u (atomic weight of Bromine-81)Nuclide mass:80.8970886 u (calculated nuclear mass without electrons)Mass excess:-77.40715 MeVMass defect:0.755562256 u (per nucleus)Nuclear binding energy:703.80170809 MeV (per nucleus)
8.68890998 MeV (average binding energy per nucleon)Separation energy:SN = 10.1593(14) MeV (first neutron)
SP = 7.5065(14) MeV (first proton)Half-life:stableSpin and parity:
(nuclear angular momentum)3/2-Magnetic dipole moment:μ(μN) = +2.2686(6)Charge radius:4.1599(21) femtometer fmYear of discovery:1920
Parent Nuclides
Direct parent isotopes are: 81Kr, 81Se.
Occurrence
Comparison of the natural Bromine isotopes including isotopic abundance (mole fraction of the isotope mixture in percent):
| | Atomic Mass ma | Quantity | Half-life | Spin |
|---|
Bromine
Isotopic mixture | 79.904 u | 100 % | | |
| Isotope 81Br | 80.9162882(10) u | 49.35 %
[49.2 - 49.5 %] | stable | 3/2- |
| Isotope 79Br | 78.9183376(11) u | 50.65 %
[50.5 - 50.8 %] | stable | 3/2- |
NMR data
Nuclear magnetic properties and parameters of the NMR active Nuclide 81Br
Isotope:81Br-NMRQuantity:49.35 % [49.2 - 49.5 %]Spin:3/2-Nuclearmagnetic moment
μ/μN:+2.2686(6)Gyromagnetic ratio γ:7.249776 · 107 rad T-1 s-1
11.53838 MHz T-1Nuclear g-factor:gl = 1.5124Quadrupole moment Q:+0.2579(2) barn (100 fm2)Line width parameter (factor):l = 886.83 fm4Resonance frequency:v0 = 11.5384 MHz at 1 TRelative Sensitivity:[related to 1H = 1.000]:
0.09951 (H0 = const.)
1.3550 (v0 = const.)
0.0491 (at natural abundance)
relative receptivity as compared to 13C:
288 (at natural abundance)
584 (enriched)Reference compound:
(conditions)IUPAC Recommendation: 0.01 M sodium bromide solution NaBr in deuterium oxide D2O.Frequency ratio:Ξ(81Br) = 27.006518 % [based on the reference substance]Chemical shift range:ca. 600 ppm [-500 to +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 |
|---|
| 81mBr | 536.20(9) keV | 34.6(28) μs | 9/2+ |
Isotones and Isobars
The following table shows the atomic nuclei that are isotonic (same neutron number N = 46) and isobaric (same nucleon number A = 81) with Bromine-81. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.
| Z | Isotone N = 46 | Isobar A = 81 |
|---|
| 25 | 71Mn | |
| 26 | 72Fe | |
| 27 | 73Co | |
| 28 | 74Ni | |
| 29 | 75Cu | 81Cu |
| 30 | 76Zn | 81Zn |
| 31 | 77Ga | 81Ga |
| 32 | 78Ge | 81Ge |
| 33 | 79As | 81As |
| 34 | 80Se | 81Se |
| 35 | 81Br | 81Br |
| 36 | 82Kr | 81Kr |
| 37 | 83Rb | 81Rb |
| 38 | 84Sr | 81Sr |
| 39 | 85Y | 81Y |
| 40 | 86Zr | 81Zr |
| 41 | 87Nb | 81Nb |
| 42 | 88Mo | 81Mo |
| 43 | 89Tc | |
| 44 | 90Ru | |
| 45 | 91Rh | |
| 46 | 92Pd | |
| 47 | 93Ag | |
| 48 | 94Cd | |
External data and identifiers
Literature and References
[1] - F. W. Aston:
The Constitution of the Elements.
In: Nature, 105, 547, (1920), DOI 10.1038/105547a0.
Last update: 2026-01-23
Perma link: https://www.chemlin.org/isotope/bromine-81
© 1996 - 2026 ChemLin
