Magnetic Susceptibility of Neptunium Hexafluoride in Uranium Hexafluoride

The magnetic susceptibilities of solid solutions of NpF6 in UF6 have been measured by the Faraday method. Measurements have been made on solutions with mole fractions 0.0000, 0.0407, 0.0972, 0.1806, 0.340, 0.646, and 1.000 NpF6 and over the temperature range from the boiling point of liquid He to 336.9°K. The susceptibilities χ of Np+6 so determined have been fitted by equations of the form χ=χ0+gs2Nβ2/4kT=χ0+0.09380 gs2/Tat the lower concentrations of NpF6, and by χ=χ0+gs2Nβ2/4kT+A/T2at the higher concentrations of NpF6. The values of | gs | and χ0 extrapolated to infinite dilution are 0.605 and 165×10−6 cm3 mole−1, respectively, using unrationalized Maxwell equations. The standard deviations of these values are 0.004 and 20×10−6, respectively. There is no observable variation of χ0 with concentration of NpF6 in UF6. | gs | is observed to increase from the value 0.641 for pure NpF6 and to pass through a maximum value 0.694 for the 0.340 mole fraction sample as the concentration of NpF6 is decreased. The susceptibilities of solutions of 0.646 mole fraction NpF6 in UF6 above the melting point are lower by about 10 times the error of the determination than those given by (b) when (b) is fitted to only those measurements made below the melting point. They are lower by approximately 4%. The value of the susceptibility of pure UF6 is found to be (43.7±2.6)×10−6 cm3 mole−1 independent of temperature. The value of the susceptibility of fused silica is found to be (−0.412±0.005)×10−6 cm3 g−1 and is independent of temperature. The measurements for NpF6 are compared with the results of the studies of paramagnetic resonance of NpF6 and with theoretical discussions of the electronic states of this molecule.