Thallium-203
Properties and data of the isotope 203Tl.
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
Parent Nuclides
Direct parent isotopes are: 203Pb, 203Hg.
Occurrence
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 205Tl | 204.974428(9) u | 70.48(1) %
[70.41 - 70.56 %] | stable | 1/2+ |
| Isotope 203Tl | 202.972345(9) u | 29.52(1) %
[29.44 - 29.59 %] | stable | 1/2+ |
NMR data
Nuclear magnetic properties and parameters of the NMR active Nuclide 203Tl
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.
| Z | Isotone N = 122 | Isobar A = 203 |
|---|
| 74 | 196W | |
| 75 | 197Re | |
| 76 | 198Os | 203Os |
| 77 | 199Ir | 203Ir |
| 78 | 200Pt | 203Pt |
| 79 | 201Au | 203Au |
| 80 | 202Hg | 203Hg |
| 81 | 203Tl | 203Tl |
| 82 | 204Pb | 203Pb |
| 83 | 205Bi | 203Bi |
| 84 | 206Po | 203Po |
| 85 | 207At | 203At |
| 86 | 208Rn | 203Rn |
| 87 | 209Fr | 203Fr |
| 88 | 210Ra | 203Ra |
| 89 | 211Ac | 203Ac |
| 90 | 212Th | |
| 91 | 213Pa | |
| 92 | 214U | |
External data and identifiers
Literature and References
[1] - F. W. Aston:
Constitution of Thallium and Uranium.
In: Nature, 128, 725, (1931), DOI 10.1038/128725a0.
[2] - Roy E. Hoffman:
Thallium chemical shift referencing.
In: Journal of Magnetic Resonance, 326, 106944, (2021), DOI 10.1016/j.jmr.2021.106944.
Last update: 2025-12-17
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