Promethium, with the chemical symbol Pm and atomic number 61, is a radioactive element with no stable isotopes. Discovered in 1945 by scientists Jacob A. Marinsky, Lawrence E. Glendenin, and Charles D. Coryell, it was identified through the analysis of uranium residues and named after the Greek Titan Prometheus.

On Earth, promethium is extremely rare and does not occur naturally as all its isotopes are radioactive and decay over time. It is produced as an intermediate product in the nuclear fission of uranium and thorium but in minute quantities. Promethium found applications in instrument glow markers.

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