Experiments on random packings of ellipsoids

Recent simulations indicate that ellipsoids can pack randomly more densely than spheres and, remarkably, for axes ratios near 1.25 1 0.8 can approach the densest crystal packing (fcc) of spheres, with a packing fraction of 74%. We demonstrate that such dense packings are realizable. We introduce a novel way of determining packing density for a finite sample that minimizes surface effects. We have fabricated ellipsoids and show that, in a sphere, the radial packing fraction (r) can be obtained from V(h), the volume of added fluid to fill the sphere to height h. We also obtain (r) from a magnetic resonance imaging scan. The measurements of the overall density avr, (r) and the core density 0=0.74±0.005 agree with simulations.