Some astronomical observatories use laser guide stars to excite this element in the atmosphere because that creates a wavefront reference for adaptive optics. An experimental type of nuclear reactor cooled by this element, sometimes in an alloy with 
Some astronomical observatories use laser guide stars to excite this element in the atmosphere because that creates a wavefront reference for adaptive optics. An experimental type of nuclear reactor cooled by this element, sometimes in an alloy with potassium, includes the extremely accident-plagued Monju Nuclear Power Plant. Pretty much all of the solid form of this element used commercially is prepared using a mixture of it and calcium chloride in a Downs cell. The solvent for aluminum oxide in the HallÂ–Héroult (ay-ROO) process is a mixture of aluminum and this element bound to fluoride; that mixture is cryolite. A 588.99 and 589.59 nanometer doublet in an astronomical object's spectrum corresponds to this element's D lines. For 10 points, name this element that forms a molten salt above 801 degrees Celsius when bound to chlorine.
Some astronomical observatories use laser guide stars to excite this element in the atmosphere because that creates a wavefront reference for adaptive optics.