Noun: protoactinium ,prow-tow,ak'ti-nee-um
Usage: rare (=protactinium)
Usage: rare (=protactinium)
- A radioactive metallic element formed from uranium and disintegrating into actinium and then into lead
"Protoactinium, atomic number 91, is one of the rarest naturally occurring elements";
- protactinium, Pa, atomic number 91
Type of: metal, metallic element
Encyclopedia: Protoactinium