Terbium-175

Properties and data of the isotope ¹⁷⁵Tb.

Contents

Terbium-175 is a radioisotope of the chemical element terbium, which has 110 neutrons in its atomic nucleus in addition to the element-specific 65 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 175. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of ¹⁷⁵Tb is exclusively for academic purposes.

The discovery of the extremely neutron-rich isotope terbium-175 was reported for the first time in January 2026. It was produced via in-flight projectile fragmentation of a high-energy uranium-238 beam - with an energy of 345 MeV per nucleon - impinging on a beryllium target at the RIKEN RI Beam Factory, with subsequent detection achieved using the BigRIPS separator. Neither mass nor other physical parameters were measured in the experiment [1].

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

General data

Name of the isotope:Terbium-175; Tb-175Symbol:¹⁷⁵Tb or 17565TbMass number A:175 (= number of nucleons)Atomic number Z:65 (= number of protons)Neutrons N:110Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.6923076923077 (= neutron-proton ratio)Neutron excess (N-Z):45Isotopic mass:175 u (atomic weight of Terbium-175)Nuclide mass:174.9643453 u (calculated nuclear mass without electrons)Mass excess:0 MeVMass defect:1.46176784 u (per nucleus)Nuclear binding energy:1361.62797235 MeV (per nucleus)
7.78073127 MeV (average binding energy per nucleon)Half-life:Spin and parity:
(nuclear angular momentum)Year of discovery:2026

Radioactive Decay

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β^- ?

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 110) and isobaric (same nucleon number A = 175) with Terbium-175. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 110	Isobar A = 175
65	¹⁷⁵Tb	¹⁷⁵Tb
69	¹⁷⁹Tm	¹⁷⁵Tm
70	¹⁸⁰Yb	¹⁷⁵Yb
71	¹⁸¹Lu	¹⁷⁵Lu
72	¹⁸²Hf	¹⁷⁵Hf
73	¹⁸³Ta	¹⁷⁵Ta
74	¹⁸⁴W	¹⁷⁵W
75	¹⁸⁵Re	¹⁷⁵Re
76	¹⁸⁶Os	¹⁷⁵Os
77	¹⁸⁷Ir	¹⁷⁵Ir
78	¹⁸⁸Pt	¹⁷⁵Pt
79	¹⁸⁹Au	¹⁷⁵Au
80	¹⁹⁰Hg	¹⁷⁵Hg
81	¹⁹¹Tl
82	¹⁹²Pb
83	¹⁹³Bi
84	¹⁹⁴Po
85	¹⁹⁵At
86	¹⁹⁶Rn

Literature and References

[1] - Toshiyuki Sumikama, Naoki Fukuda, Toshiyuki Kubo et al.:
Toshiyuki Sumikama, Naoki Fukuda, Toshiyuki Kubo et al..
In: Journal of the Physical Society of Japan, 95, 2, (2026), DOI 10.7566/JPSJ.95.024202.