31. Protactinium exhibits two valence states; the + 5 is stable, and the + 4 state easily oxidizes to protactinium ( V ).32. Protactinium exhibits two valence states; the + 5 is stable, and the + 4 state easily oxidizes to protactinium ( V ). 33. The thorium-233 beta decays to protactinium -233 and then to uranium-233, which in turn is used as fuel. 34. Protactinium metal can be prepared by reduction of its fluoride with calcium fluoride, lithium or barium at a temperature of 1300 1400 �C.35. In the thorium cycle, thorium-232 breeds by converting first to protactinium -233, which then decays to uranium-233. 36. The room temperature value for americium is lower than that of neptunium, plutonium and curium, but higher than for uranium, thorium and protactinium . 37. The new element was called brevium due to the short half-life of the isotope specific studied, Protactinium -234 ( 234 Pa ). 38. The complex chemical behavior of protactinium is a consequence of the start of the filling of the 5 " f " shell in this element. 39. Thorium's melting point of 1750 �C is above both that of actinium ( 1227 �C ) and that of protactinium ( approximately 1560 �C ). 40. Different isotopes of protactinium were identified in Germany in 1913 and in 1918, but the name " protactinium " was not given until 1948.
