Anomalous elastic response of silicon to uniaxial shock compression on nanosecond time scales

We have used x-ray diffraction with subnanosecond temporal resolution to me asure the: lattice parameters of orthogonal planes in shock compressed sing le crystals of silicon (Si) and copper (Cu). Despite uniaxial compression a long the (400) direction of Si reducing the lattice spacing by nearly 11%, no observable changes occur in planes with normals orthogonal to the shock propagation direction; In contrast, shocked Cu shows prompt hydrostaticlike compression. These results are consistent with simple estimates of plastic strain rates based on dislocation velocity data.