[gippgig]

A recent paper (Physical Review C 76 021303(R)) reports evidence for trace amounts of thorium isotopes with masses 211, 213, 217, & 218. The authors ascribe this to unusual long-lived isomers, the existence of which is not generally accepted. (The IUPAC/IUPAP Joint Working Party on discovery of new elements dismissed a related claim by this group to have made element 112, saying, "The JWP is unconvinced.") This is probably some sort of artifact, but the experiment should be repeated independently. The obvious next step is to further purify the thorium & see whether the signals are still associated with thorium or appear in an impurity fraction (if they still occur at all).

One long-lived nuclear isomer is known, Ta-180m, which has a lifetime so long its decay has never been observed. This nuclide is easy to identify because its mass differs from ordinary Ta-181 - but what if a long-lived isomer existed of a stable nuclide (for example, suppose Os-187 is 99% ground state & 1% isomer)? Could this have escaped notice? (I suspect - but am not sure - that study or prediction of nuclear energy levels would reveal that something funny was going on.) Has anyone looked for this? Also, if such an isomer did exist, would there be any way to enrich it?

[gippgig]

This experiment has now been repeated independently (Physical Review C 78 064313) using the more sensitive technique of accelerator mass spectrometry. No evidence was found for any of these nuclides, which also discredits similar claims for an assortment of other exotic nuclides including element 122 (see the entry "A report of Z=122 in nature"). This is not at all surprising but it's really nice that someone bothered to do the work to disprove the claim since once in a while one of these far-fetched claims turns out to be correct (see amorphous semiconductors).