pro.tac.tin.i.um
n.Symbol Pa （名词）符号 Pa A rare, extremely toxic, radioactive element chemically similar to uranium, having 3 known isotopes, the most common of which is protactinium 23 with a half-life of 32,480 years. Atomic number 9; melting point ,230=C; specific gravity 5.37; valence 4, 5.See table at element 镤：一种稀有的、剧毒放射性元素，在化学性质上与铀相似。有十三个已知的同位素，其中最常见的是半衰期为32,480年的镤23。原子序数为9；熔点,230=C；比重5.37；原子价4, 5参见 element
来源：prot(o)- prot(o)-actinium [so called because it disintegrates into actinium] actinium [它被这样取名是由于它分裂成锕]
