Thallium-203 is a radioisotope of the chemical element thallium, which has 122 neutrons in its atomic nucleus in addition to the element-specific 81 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 203.
The first observation and identification of the nuclide 203Tl using a Cavendish mass spectrometer was reported in 1931 [1].
See also: List of individual Thallium isotopes (and general data sources).
General data
Name of the isotope:Thallium-203; Tl-203Symbol:203Tl or 20381TlMass number A:203 (= number of nucleons)Atomic number Z:81 (= number of protons)Neutrons N:122Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.5061728395062 (= neutron-proton ratio)Neutron excess (N-Z):41Isotopic mass:202.972345(9) u (atomic weight of Thallium-203)Nuclide mass:202.927915 u (calculated nuclear mass without electrons)Mass excess:-25.76047 MeVMass defect:1.718602344 u (per nucleus)Nuclear binding energy:1600.86777182 MeV (per nucleus) 7.88604814 MeV (average binding energy per nucleon)Separation energy:SN = 7.8525(15) MeV (first neutron) SP = 5.7050(11) MeV (first proton)Half-life:stableSpin and parity: (nuclear angular momentum)1/2+Magnetic dipole moment:μ(μN) = + 1.62225787(12)Charge radius:5.4666(27) femtometer fmYear of discovery:1931
Comparison of the natural Thallium isotopes including isotopic abundance (mole fraction of the isotope mixture in percent):
Atomic Mass ma
Quantity
Half-life
Spin
Thallium Isotopic mixture
204.38 u
100 %
Isotope 203Tl
202.972345(9) u
29.52(1) % [29.44 - 29.59 %]
stable
1/2+
Isotope 205Tl
204.974428(9) u
70.48(1) % [70.41 - 70.56 %]
stable
1/2+
NMR data
Nuclear magnetic properties and parameters of the NMR active Nuclide203Tl
Isotope:203Tl-NMRQuantity:29.52(1) % [29.44 - 29.59 %]Spin:1/2+Nuclearmagnetic moment μ/μN:+ 1.62225787(12)Gyromagnetic ratio γ:15.5394 · 107 rad T-1 s-1 24.73172 MHz T-1Nuclear g-factor:gl = 3.24451574Resonance frequency:v0 = 24.7316 MHz at 1 TRelative Sensitivity:[related to 1H = 1.000]: 0.19598 (H0 = const.) 0.5809 (v0 = const.) 0.0579 (at natural abundance) relative receptivity as compared to 13C: 340 (at natural abundance)Reference compound: (conditions)A very dilute solution of thallium(I) nitrate in water (The highly hydrolysis-sensitive thallium(III) nitrate is incorrectly listed in some publications).Frequency ratio:Ξ(203Tl) = 57.123200 % [based on the reference substance]
Isotones and Isobars
The following table shows the atomic nuclei that are isotonic (same neutron number N = 122) and isobaric (same nucleon number A = 203) with Thallium-203. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.
