Astatine-188

Properties and data of the isotope ¹⁸⁸At.

Contents

Astatine-188 is a radioisotope of the chemical element astatine, which has 103 neutrons in its atomic nucleus in addition to the element-specific 85 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 188. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of ¹⁸⁸At is exclusively for academic purposes.

The proton-emitting nuclide was first reported in 2025 after it was produced by the fusion-evaporation reaction ¹⁰⁷Ag(⁸⁴Sr,3n)¹⁸⁸At and observed (2 events) with the focal plane spectrometer of the gas-filled recoil separator in the accelerator laboratory of the University of Jyväskylä in Finland [1].

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

General data

Name of the isotope:Astatine-188; At-188Symbol:¹⁸⁸At or 18885AtMass number A:188 (= number of nucleons)Atomic number Z:85 (= number of protons)Neutrons N:103Isotopic mass:188 u (atomic weight of Astatine-188)Nuclide mass:187.9533763 u (calculated nuclear mass without electrons)Mass excess:0 MeVMass defect:1.557614068 u (per nucleus)Nuclear binding energy:1450.90815866 MeV (per nucleus)
7.71759659 MeV (average binding energy per nucleon)Half-life:190 μsSpin and parity:
(nuclear angular momentum)Year of discovery:2025

Radioactive Decay

Half-life T_½ = 190 μs.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	¹⁸⁵Bi	ca. 50 &	7.9(2) MeV
p	¹⁸⁷Po	ca. 50 %	1.50(4) keV

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 103) and isobaric (same nucleon number A = 188) with Astatine-188. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 103	Isobar A = 188
60	¹⁶³Nd
62	¹⁶⁵Sm
63	¹⁶⁶Eu
64	¹⁶⁷Gd
65	¹⁶⁸Tb
66	¹⁶⁹Dy
67	¹⁷⁰Ho
68	¹⁷¹Er
69	¹⁷²Tm
70	¹⁷³Yb
71	¹⁷⁴Lu	¹⁸⁸Lu
72	¹⁷⁵Hf	¹⁸⁸Hf
73	¹⁷⁶Ta	¹⁸⁸Ta
74	¹⁷⁷W	¹⁸⁸W
75	¹⁷⁸Re	¹⁸⁸Re
76	¹⁷⁹Os	¹⁸⁸Os
77	¹⁸⁰Ir	¹⁸⁸Ir
78	¹⁸¹Pt	¹⁸⁸Pt
79	¹⁸²Au	¹⁸⁸Au
80	¹⁸³Hg	¹⁸⁸Hg
81	¹⁸⁴Tl	¹⁸⁸Tl
82	¹⁸⁵Pb	¹⁸⁸Pb
83	¹⁸⁶Bi	¹⁸⁸Bi
84	¹⁸⁷Po	¹⁸⁸Po
85	¹⁸⁸At	¹⁸⁸At

Literature and References

[1] - Henna Kokkonen, Kalle Auranen, Pooja Siwach et al.:
New proton emitter ¹⁸⁸At implies an interaction unprecedented in heavy nuclei.
In: Natur Communications, 16, 4985, (2025), DOI 10.1038/s41467-025-60259-6.