Thallium-201

Properties and data of the isotope ²⁰¹Tl.

Contents

General Data

Radioactive Decay

Parent Nuclides

Isotones und Isobares

Literature

Thallium-201 is a radioisotope of the chemical element thallium, which has 120 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 201. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of ²⁰¹Tl is exclusively for academic purposes and experimental research.

A report on the first observation of the nuclide ²⁰¹Tl was published in 1950 [1].

See also: List of individual Thallium isotopes (and general data sources).

General data

Name of the isotope:Thallium-201; Tl-201Symbol:²⁰¹Tl or 20181TlMass number A:201 (= number of nucleons)Atomic number Z:81 (= number of protons)Neutrons N:120Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.4814814814815 (= neutron-proton ratio)Neutron excess (N-Z):39Isotopic mass:200.970820(15) u (atomic weight of Thallium-201)Nuclide mass:200.92639 u (calculated nuclear mass without electrons)Mass excess:-27.18099 MeVMass defect:1.702797512 u (per nucleus)Nuclear binding energy:1586.14566564 MeV (per nucleus)
7.89127197 MeV (average binding energy per nucleon)Separation energy:S_N = 8.205(15) MeV (first neutron)
S_P = 4.966(14) MeV (first proton)Half-life:3.0420(16) dDecay constant λ:2.637255327836 × 10^-6 s^-1Specific activity α:7.940961533925 × 10⁺¹⁵ Bq g^-1
214620.58199798 Ci g^-1Spin and parity:
(nuclear angular momentum)1/2+Magnetic dipole moment:μ(μ_N) = + 1.599(3)Nuclear g-factor:g_l = 3.198Charge radius:5.4573(29) femtometer fmYear of discovery:1950

Radioactive Decay

Half-life T_½ = 3.0420(16) d respectively 2.62829 × 10⁵ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
EC	²⁰¹Hg	100 %	0.482(14) MeV

Parent Nuclides

Direct parent isotope is: ²⁰¹Pb.

Nuclear Isomers

Nuclear isomers or excited states with the activation energy in keV related to the ground state.

Nuclear Isomer	Excitation Energy	Half-life	Spin
^201mTl	919.47(11) keV	2.11(11) ms	(9/2-)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 120) and isobaric (same nucleon number A = 201) with Thallium-201. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 120	Isobar A = 201
73	¹⁹³Ta
74	¹⁹⁴W
75	¹⁹⁵Re
76	¹⁹⁶Os	²⁰¹Os
77	¹⁹⁷Ir	²⁰¹Ir
78	¹⁹⁸Pt	²⁰¹Pt
79	¹⁹⁹Au	²⁰¹Au
80	²⁰⁰Hg	²⁰¹Hg
81	²⁰¹Tl	²⁰¹Tl
82	²⁰²Pb	²⁰¹Pb
83	²⁰³Bi	²⁰¹Bi
84	²⁰⁴Po	²⁰¹Po
85	²⁰⁵At	²⁰¹At
86	²⁰⁶Rn	²⁰¹Rn
87	²⁰⁷Fr	²⁰¹Fr
88	²⁰⁸Ra	²⁰¹Ra
89	²⁰⁹Ac
90	²¹⁰Th

External data and identifiers

Adopted Levels, Gammas:NuDat 201Tl

Literature and References

[1] - Alex Rigby, George Firth, Charlotte Rivas et al.:
Toward Bifunctional Chelators for Thallium-201 for Use in Nuclear Medicine.
In: Bioconjugate Chemistry, 33, 7, (2022), DOI 10.1021/acs.bioconjchem.2c00284.

[2] - Sankha Chattopadhyay, Luna Barua, D.G. Mahesh et al.:
Production of pharmaceutical grade [²⁰¹Tl]Thallous chloride using 30 MeV cyclotron.
In: Applied Radiation and Isotopes, 204, 111128, (2024), DOI 10.1016/j.apradiso.2023.111128.