Thallium-205 is a stable isotope of the chemical element thallium, which has 124 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 205.
The first observation and identification of the nuclide 205Tl 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-205; Tl-205Symbol:205Tl or 20581TlMass number A:205 (= number of nucleons)Atomic number Z:81 (= number of protons)Neutrons N:124Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.5308641975309 (= neutron-proton ratio)Neutron excess (N-Z):43Isotopic mass:204.974428(9) u (atomic weight of Thallium-205)Nuclide mass:204.929998 u (calculated nuclear mass without electrons)Mass excess:-23.82016 MeVMass defect:1.733849176 u (per nucleus)Nuclear binding energy:1615.07010435 MeV (per nucleus) 7.87839075 MeV (average binding energy per nucleon)Separation energy:SN = 7.5461(5) MeV (first neutron) SP = 6.4196(13) MeV (first proton)Half-life:stableSpin and parity: (nuclear angular momentum)1/2+Magnetic dipole moment:μ(μN) = + 1.6382146Charge radius:5.4759(26) 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 Nuclide205Tl
Isotope:205Tl-NMRQuantity:70.48(1) % [70.41 - 70.56 %]Spin:1/2+Nuclearmagnetic moment μ/μN:+ 1.6382146Gyromagnetic ratio γ:15.6922 · 107 rad T-1 s-1 24.97491 MHz T-1Nuclear g-factor:gl = 3.2764292Resonance frequency:v0 = 24.9749 MHz at 1 TRelative Sensitivity:[related to 1H = 1.000]: 0.20182 (H0 = const.) 0.5866 (v0 = const.) 0.142 (at natural abundance) relative receptivity as compared to 13C: 836 (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(205Tl) = 57.68383 % [based on the reference substance]
205Tl is the more sensitive and less broad line-producing atomic nucleus of the two natural NMR-active isotopes thallium-203 and Thallium-205, which is why it is more frequently used for Tl-NMR spectroscopy.
Nuclear Isomers
Nuclear isomers or excited states with the activation energy in keV related to the ground state.
The following table shows the atomic nuclei that are isotonic (same neutron number N = 124) and isobaric (same nucleon number A = 205) with Thallium-205. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.
