Criteria for the discovery of nuclides (or isotopes) were established within the Discovery of Nuclides Project at the Facility for Rare Isotope Beams at Michigan State University.
The discovery of isomers following the criteria listed below were published in 2026.
In most cases, the discovery is easy to determine. However, there are cases that are controversial for many different reasons.
Discovery of Isotopes
The following guidelines were used to determine the claim of discovery of an isotope of an element:
- Clean identification, Either by decay curves (half-lives) and relationships to other known isotopes, particle or γ-ray spectra, or unique mass and Z identification
- The discovery had to be reported in a refereed journal
- The submission date is adopted as the date of discovery
- In case two discovery articles were submitted on the same date, the article which was published first received the credit for the discovery
- If the half-life was used as identification it had to agree with the later established half-life within about a factor of two
Discovery of Isomers
The following guidelines were used to determine the claim of discovery of an isomer:
- Half-lives of more than 100 ns
- Clean identification, either by decay curves (half-lives) and relationships to other known isotopes, particle or γ-ray spectra, or unique mass and Z identification
- The metastability of the isomer had to be measured, which in most cases was the half-life
- The discovery had to be reported in a refereed journal
- The submission date is adopted as the date of discovery
- If only a lower half-life limit was reported, the decay energy had to be determined
- If the discovery of an isotope involved the observation of only one state which could have been the ground state or an isomer, the subsequent observation of a second state−either the ground state or an isomer−is counted as the discovery of isomerism