Boron-11

Properties and data of the isotope ¹¹B.

Contents

General Data

Parent Nuclides

NMR Data

Isotones und Isobares

Literature

Boron-11 - which together with boron-10 in a ratio of about 4:1 forms the naturally occurring terrestrial element boron, is a stable isotope whose atomic nucleus consists of 6 neutrons and the element-specific 5 protons; the sum of these nucleons results in the mass number 11.

The simultaneous discovery of both isotopes was reported in 1920; the identification was carried out based on the evaluation of mass spectra of natural boron samples [1].

General data

Name of the isotope:Boron-11; B-11Symbol:¹¹B or 115BMass number A:11 (= number of nucleons)Atomic number Z:5 (= number of protons)Neutrons N:6Isotopic mass:11.009305(3) u (atomic weight of Boron-11)Nuclide mass:11.0065621 u (calculated nuclear mass without electrons)Mass excess:8.66755 MeVMass defect:0.081809656000001 u (per nucleus)Nuclear binding energy:76.20520371 MeV (per nucleus)
6.92774579 MeV (average binding energy per nucleon)Separation energy:S_N = 11.454221(19) MeV (first neutron)
S_P = 11.22875(8) MeV (first proton)Half-life:stableSpin and parity:
(nuclear angular momentum)3/2-Isobaric spin: 1/2Magnetic dipole moment:μ(μ_N) = 2.688378(1)Charge radius:2.4060(294) femtometer fmMirror nucleus:Carbon-11Year of discovery:1920

Parent Nuclides

Direct parent isotopes are: ¹¹Be, ¹¹C.

Occurrence

Comparison of the natural Boron isotopes including isotopic abundance (mole fraction of the isotope mixture in percent):

	Atomic Mass m_a	Quantity	Half-life	Spin
Boron Isotopic mixture	10.81 u	100 %
Isotope ¹⁰B	10.012937(3) u	19.65 % [18.9 - 20.4 %]	stable	3+
Isotope ¹¹B	11.009305(3) u	80.35 % [79.6 - 81.1 %]	stable	3/2-

NMR data

Nuclear magnetic properties of the NMR active Nuclide ¹¹B

Isotope:¹¹B-NMRQuantity:80.35 % [79.6 - 81.1 %]Spin:3/2-Nuclearmagnetic moment
μ/μ_N:2.688378(1)Gyromagnetic ratio γ:8.584 · 10⁷ rad T^-1 s^-1Nuclear g-factor:g_l = 1.792252Quadrupole moment Q:0.04059(10) barn (100 fm²)Line width parameter (factor):l = 21.97 fm⁴Resonance frequency:v₀ = 13.6630 at 1 TFrequency ratio:Ξ(¹¹B) = 32.083974 %Relative Sensitivity:0.16522 (H₀ = const.)
1.6045 (v₀ = const.)
[related to ¹H = 1.000]Reference compound:
(conditions)Boron trifluoride etherate BF₃ × OEt₂ in chloroform-d as solvent.

The atomic nuclei of both natural boron isotopes are quadrupolar and are suitable for NMR spectroscopic measurements. ¹¹B with a spin of 3/2 and a lower quadrupole moment is, however, more sensitive and shows sharper signals in the spectrum.

In practice, it should be noted that glass for NMR measurements may contain boron (borosilicate glass), which can distort the measurement and lead to broader NMR signals. If necessary, the sample tubes should be replaced with quartz glass.

¹¹B NMR spectroscopy is used to determine the structure of boron-containing compounds. A special application is quantitative boron 11 NMR spectroscopy (¹¹B qNMR) for measuring, for example, the boric acid content of a sample [2].

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 6) and isobaric (same nucleon number A = 11) with Boron-11. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.