Barium-155 is a radioisotope of the chemical element barium, which has 99 neutrons in its atomic nucleus in addition to the element-specific 56 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 155. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of ¹⁵⁵Ba is exclusively for academic purposes.

The discovery of the extremely neutron-rich isotope barium-155 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 Barium isotopes (and general data sources).

General data

Isotones and Isobars

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.

Last update: 2026-06-10

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