The silicon-28 path to the Avogadro constant-first experiments and outlook

For the first time an attempt has been made to determine the lattice parameter, density, and molar mass of an isotopically highly enriched silicon-28 crystal. The goal was to achieve an independent value of Avogadro's constant of accuracy equal or superior to current best values obtained from similar measurements of very pure and highly perfect silicon single crystals of natural isotopic composition. That aim has been foiled by unexplained contaminations of the /sup 28/Si crystal and perhaps other unidentified causes. Under these circumstances this paper restricts itself to a brief record of the method used and the results obtained. The value of the Avogadro constant so derived is considered of no further significance and differs from the CODATA and other credible values by about 1/spl middot/10-/sup 5/N/sub A/.>