Discovery date : 1913
Discovered by: Kasimir Fajans and Otto Göhring
Origin of the name: The name is derived from the Greek 'protos',
meaning first, as a prefix to the element actinium,
which is produced through the radioactive decay of proactinium.
Allotropes :
~>PROTACTINIUM is a chemical element with symbol Pa and atomic number 91. It is a dense, silvery-gray metal which readily reacts with oxygen, water vapor and inorganic acids.
| FACT BOX | |||
| Group | Actinides | Melting point | 1572°C, 2862°F, 1845 K |
| Period | 7 | Boiling point | 4000°C, 7232°F, 4273 K |
| Block | f | Density (g cm−3) | 15.4 |
| Atomic number | 91 | Relative atomic mass | 231.036 |
| State at 20°C | Solid | Key isotopes | 231Pa |
| Electron configuration | [Rn] 5f26d17s2 | CAS number | 7440-13-3 |
| ChemSpider ID | 22387 | ChemSpider is a free chemical structure database | |
Mendeleev said there should be an element between thorium and uranium, but it evaded detection. Then, in 1900, William Crookes separated an intensely radioactive material from uranium, but did not identify it. In 1913, Kasimir Fajans and Otto Göhring showed that this new element decayed by beta-emission and it existed only fleetingly. We now know it is a member of the sequence of elements through which uranium decays. It was the isotope protactinium-234, which has a half-life of 6 hours 42 minutes.
A longer-lived isotope was separated from the uranium ore pitchblende (uranium oxide, U3O8) in 1918 by Lise Meitner at the Kaiser-Wilhelm Institute in Berlin. This was the longer-lived isotope protactinium-231, also coming from uranium, and its half-life is 32,500 years.
In 1934, Aristid von Grosse reduced protactinium oxide to protactinium metal by decomposing its iodide (PaF5) on a heated filament.