Lattice Constants of Separated Lithium Isotopes

Abstract

The lattice constant for highly enriched (>99%) samples of Li⁶ and Li⁷ metal was determined at 20°C by x‐ray diffraction methods. The constant for Li⁶ was found to be fractionally larger than that for Li⁷ by about 4×10^—4. These results are not inconsistent with a rough theoretical estimate for the fractional difference of 3×10^—4. It is likely that the constant for Li⁷ does not differ from that for natural lithium by more than 1×10^—4. The fact that the lighter isotope has the larger lattice constant constitutes experimental evidence for the reality of zero‐point energy.