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Other theorists have predicted that hydrides such as calcium hydride or actinium hydride should superconduct at close to room temperature—and at a pressure considerably less than that needed for CSH.

But other heavy elements could, like actinium, which is a bit lighter with 89 protons and 89 electrons.

The substance in question, actinium-227, emits alpha and beta radiation, both of which are charged particles.

NRC investigators determined that the powder was actinium-227, a radioactive isotope, according to a Jan. 31 letter summarizing the incident.

Traditionalists maintain that these comprise scandium, yttrium, lanthanum and actinium; a growing number thinks that lutetium and lawrencium should replace the last two on the basis of electronic structures.