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abbreviation of "public address" (system), attested from 1936.
The symbol for the element protactinium.
PA or P.A.
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.
The country code for Panama.