Phosphorus-31 is a stable, naturally occurring isotope of the chemical element phosphorus, which has 16 neutrons in its atomic nucleus in addition to the element-specific 15 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 31.
Phosphorus-31 was first identified as a distinct isotope in 1920 by measuring its mass spectrum [1].
See also: List of individual Phosphorus isotopes (and general data sources).
General data
Name of the isotope:Phosphorus-31; P-31Symbol:31P or 3115PMass number A:31 (= number of nucleons)Atomic number Z:15 (= number of protons)Neutrons N:16Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.0666666666667 (= neutron-proton ratio)Neutron excess (N-Z):1Isotopic mass:30.9737619977(8) u (atomic weight of Phosphorus-31)Nuclide mass:30.9655334 u (calculated nuclear mass without electrons)Mass excess:-24.44054 MeVMass defect:0.2822521383 u (per nucleus)Nuclear binding energy:262.91617331 MeV (per nucleus) 8.48116688 MeV (average binding energy per nucleon)Separation energy:SN = 12.31101(7) MeV (first neutron) SP = 7.296553(22) MeV (first proton)Half-life:stableSpin and parity: (nuclear angular momentum)1/2+Magnetic dipole moment:μ(μN) = + 1.130925(5)Charge radius:3.1889(19) femtometer fmMirror nucleus:Sulfur-31Year of discovery:1920
Isotope:31P-NMRQuantity:100 %Spin:1/2+Nuclearmagnetic moment μ/μN:+ 1.130925(5)Gyromagnetic ratio γ:10.841 · 107 rad T-1 s-1 17.25399 MHz T-1Nuclear g-factor:gl = 2.26185Resonance frequency:v0 = 17.2515 MHz at 1 TRelative Sensitivity:[related to 1H = 1.000]: 0.06652 (H0 = const.) 0.4052 (v0 = const.) 0.0665 (at natural abundance) relative receptivity as compared to 13C: 391 (at natural abundance)Reference compound: (conditions)85% phosphoric acid (H3PO4)Frequency ratio:Ξ(31P) = 40.480742 % [based on the reference substance]
The nuclide phosphorus-31 has an atomic nucleus of medium sensitivity and a large range of chemical shifts; 31P-NMR spectra show sharp lines.
Isotones and Isobars
The following table shows the atomic nuclei that are isotonic (same neutron number N = 16) and isobaric (same nucleon number A = 31) with Phosphorus-31. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.
