Terbium-161

Properties and data of the isotope ¹⁶¹Tb.

Contents

General Data

Radioactive Decay

Parent Nuclides

Formation

Isotones und Isobares

Literature

Terbium-161 is the radioisotope of the chemical element terbium, which has 96 neutrons in its atomic nucleus in addition to the element-specific 65 protons, resulting in a mass number of 161. The radionuclide does not occur naturally on earth; the required quantities must be produced artificially (see below).

The radioactive nuclide is currently being intensively investigated with regard to its suitability and possible applications for radionuclide therapy in medicine.

General data

Name of the isotope:Terbium-161; Tb-161Symbol:¹⁶¹Tb or 16165TbMass number A:161 (= number of nucleons)Atomic number Z:65 (= number of protons)Neutrons N:96Isotopic mass:160.9275768(13) u (atomic weight of Terbium-161)Nuclide mass:160.8919221 u (calculated nuclear mass without electrons)Mass excess:-67.46178 MeVMass defect:1.412882216 u (per nucleus)Nuclear binding energy:1316.09130691 MeV (per nucleus)
8.17448017 MeV (average binding energy per nucleon)Separation energy:S_N = 7.6966(5) MeV (first neutron)
S_P = 6.8087(10) MeV (first proton)Half-life:6.934(14) dDecay constant λ:1.156985406985 × 10^-6 s^-1Specific activity α:4.354705683598 × 10⁺¹⁵ Bq g^-1
117694.74820535 Ci g^-1Spin and parity:
(nuclear angular momentum)3/2+Magnetic dipole moment:μ(μ_N) = 2.2(1)Quadrupole moment Q:+1.20(6) barn (100 fm²)Nuclear g-factor:g_l = 1.4666666666667Year of discovery:1949

Radioactive Decay

The half-life of terbium-161 has been re-determined several times in recent years - with different but close values. A recommendation for a new mean value was published in 2024 [4] and adopted here.

The official value is t_1/2 = 6.89(2) days.

Half-life T_½ = 6.934(14) d respectively 5.990976 × 10⁵ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β^-	¹⁶¹Dy	100 %	0.5937(12) MeV

Parent Nuclides

Direct parent isotope is: ¹⁶¹Gd.

Formation

Terbium-161 is produced artificially in nuclear reactors from the stable isotope Gadolinium-160 by neutron irradiation of highly enriched Gd targets and according to the following reaction:

¹⁶⁰Gd(n,γ) ¹⁶¹Gd(β^-) ¹⁶¹Tb.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 96) and isobaric (same nucleon number A = 161) with Terbium-161. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 96	Isobar A = 161
55	¹⁵¹Cs
56	¹⁵²Ba
57	¹⁵³La
58	¹⁵⁴Ce
59	¹⁵⁵Pr
60	¹⁵⁶Nd	¹⁶¹Nd
61	¹⁵⁷Pm	¹⁶¹Pm
62	¹⁵⁸Sm	¹⁶¹Sm
63	¹⁵⁹Eu	¹⁶¹Eu
64	¹⁶⁰Gd	¹⁶¹Gd
65	¹⁶¹Tb	¹⁶¹Tb
66	¹⁶²Dy	¹⁶¹Dy
67	¹⁶³Ho	¹⁶¹Ho
68	¹⁶⁴Er	¹⁶¹Er
69	¹⁶⁵Tm	¹⁶¹Tm
70	¹⁶⁶Yb	¹⁶¹Yb
71	¹⁶⁷Lu	¹⁶¹Lu
72	¹⁶⁸Hf	¹⁶¹Hf
73	¹⁶⁹Ta	¹⁶¹Ta
74	¹⁷⁰W	¹⁶¹W
75	¹⁷¹Re	¹⁶¹Re
76	¹⁷²Os	¹⁶¹Os
77	¹⁷³Ir
78	¹⁷⁴Pt
79	¹⁷⁵Au
80	¹⁷⁶Hg
81	¹⁷⁷Tl
82	¹⁷⁸Pb

External data and identifiers

CAS:14391-19-6InChI Key:GZCRRIHWUXGPOV-NJFSPNSNSA-NSMILES:[161Tb]PubChem:ID 177426Adopted Levels, Gammas:NuDat 161Tb

Literature and References

[0] - Research articles in scientific journals via PubMed: Terbium-161.

[1] - Richard P. Baum, Aviral Singh, Harshad R. Kulkarni et al.:
First-in-Humans Application of ¹⁶¹Tb: A Feasibility Study Using ¹⁶¹Tb-DOTATOC.
In: Journal of Nuclear Medicine, 62 (10), 1391-1397, (2021), DOI 10.2967/jnumed.120.258376.

[2] - Frédéric Juget, Zeynep Talip, Thierry Buchillier et al.:
Determination of the gamma and X-ray emission intensities of terbium-161.
In: Applied Radiation and Isotopes, (2021), DOI 10.1016/j.apradiso.2021.109770.

[3] - S. M. Collins,C. Gilligan, B. Pierson et al.:
Determination of the ¹⁶¹Tb half-life.
In: Applied Radiation and Isotopes, (2022), DOI 10.1016/j.apradiso.2022.110140.

[4] - Jiangpeng Dong et al.:
Determination of the half-life of ¹⁶¹Tb.
In: Applied Radiation and Isotopes, 193. 110647, (2023), DOI 10.1016/j.apradiso.2022.110647.

[5] - Grace Kong, James P. Buteau, Michael S. Hofman:
Is ¹⁶¹Tb Really Happening?.
In: Journal of Nuclear Medicine, (2024), DOI 10.2967/jnumed.124.267611.