Thermodynamics of dilute solutions of neptunium in liquid magnesium

The activity coefficient of neptunium in liquid magnesium, at 650° and 700°C, was obtained from measurements of the distribution of neptunium between a 50 mole pct MgCl2-30 mole pct NaCl-20 mole pet KC1 molten-salt solution and liquid Cd-Mg alloys. For dilute solutions of neptunium in liquid magnesium (0.04 at. pct Np) the activity coefficient of neptunium was 23.3 at 650°C and 16.0 at 700°C. The solubility of neptunium in liquid magnesium is estimated to be 4.4 at. pct (31 wt pct) at 650°C. These data are used to estimate the activity coefficient of neptunium in liquid zinc and copper.