Vapor Pressure of Neptunium

The vapor pressure of liquid neptunium metal in the temperature range 1700° to 1950°K, as determined by the Knudsen effusion technique, may be described by the equation logp(atm) = — (20 610±1280)/T+(5.10±0.70). The experimental heat and entropy of vaporization are ΔH°1800=94.3±5.9 kcal/mole, and ΔS°1800=23.3±3.2 cal/mole·deg, and the extrapolated normal boiling point of the metal is 4175°K. The neptunium specimen contained 0.56 wt. % plutonium-239, and the partial pressure of that species over the solution may be described by the equation logp(atm) = — (19 051±538)/T+(3.29±0.30).