[proh-toh-ak-tin-ee-uh
m] 
[proh-tak-tin-ee-uhm] | a radioactive, metallic element. Symbol: Pa; atomic number: 91. |
protactinium pro·tac·tin·i·um (prō'tāk-tĭn'ē-əm)
n.
Symbol Pa
A rare, extremely toxic radioactive element having 13 known isotopes, the most stable of which is Pa 231 with a half-life of 32,700 years. Atomic number 91; melting point 1,572°C; specific gravity 15.37; valence 4, 5.
| protactinium (prō'tāk-tĭn'ē-əm) Pronunciation Key
Symbol Pa A rare, extremely toxic, radioactive metallic element of the actinide series that occurs in uranium ores. It has 13 known isotopes, the most stable of which is protactinium 231 with a half-life of 32,760 years. Atomic number 91; approximate melting point 1,550°C; specific gravity 15.37; valence 4, 5. See Periodic Table. |