Lanthanum-158

Properties and data of the isotope ¹⁵⁸La.

Contents

Lanthanum-158 is a radioisotope of the chemical element lanthanum, which has 101 neutrons in its atomic nucleus in addition to the element-specific 57 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 158. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of ¹⁵⁸La is exclusively for academic purposes.

The discovery of the extremely neutron-rich isotope lanthanum-158 was first reported 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.

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

General data

Name of the isotope:Lanthanum-158; La-158Symbol:¹⁵⁸La or 15857LaMass number A:158 (= number of nucleons)Atomic number Z:57 (= number of protons)Neutrons N:101Nucleon pairing (Z - N):odd - oddNuclear ratio (N/Z ratio):1.7719298245614 (= neutron-proton ratio)Neutron excess (N-Z):44Isotopic mass:158 u (atomic weight of Lanthanum-158)Nuclide mass:157.9687331 u (calculated nuclear mass without electrons)Mass excess:0 MeVMass defect:1.32118334 u (per nucleus)Nuclear binding energy:1230.67435411 MeV (per nucleus)
7.78907819 MeV (average binding energy per nucleon)Half-life:Spin and parity:
(nuclear angular momentum)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 101) and isobaric (same nucleon number A = 158) with Lanthanum-158. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 101	Isobar A = 158
57	¹⁵⁸La	¹⁵⁸La
58	¹⁵⁹Ce	¹⁵⁸Ce
59	¹⁶⁰Pr	¹⁵⁸Pr
60	¹⁶¹Nd	¹⁵⁸Nd
61	¹⁶²Pm	¹⁵⁸Pm
62	¹⁶³Sm	¹⁵⁸Sm
63	¹⁶⁴Eu	¹⁵⁸Eu
64	¹⁶⁵Gd	¹⁵⁸Gd
65	¹⁶⁶Tb	¹⁵⁸Tb
66	¹⁶⁷Dy	¹⁵⁸Dy
67	¹⁶⁸Ho	¹⁵⁸Ho
68	¹⁶⁹Er	¹⁵⁸Er
69	¹⁷⁰Tm	¹⁵⁸Tm
70	¹⁷¹Yb	¹⁵⁸Yb
71	¹⁷²Lu	¹⁵⁸Lu
72	¹⁷³Hf	¹⁵⁸Hf
73	¹⁷⁴Ta	¹⁵⁸Ta
74	¹⁷⁵W	¹⁵⁸W
75	¹⁷⁶Re
76	¹⁷⁷Os
77	¹⁷⁸Ir
78	¹⁷⁹Pt
79	¹⁸⁰Au
80	¹⁸¹Hg
81	¹⁸²Tl
82	¹⁸³Pb
83	¹⁸⁴Bi

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.