Observation of enhancement of stopping power and possible hydrodynamic shock behavior in penetration of large molecules in solids

Measurements of the stopping power of large multiply charged ions were made by determining energy losses in thin aluminum films directly coated on solid-state detectors. With initial projectile velocities in the range of (1–5)×10⁷ cm/sec, the stopping power per amu of albumin (molecular weight M∼66290) and cytochrome c (M∼12400) increases quadratically in velocity to a maximum value of seven times that estimated for isolated atomic nitrogen moving with the same velocity. The observed velocity dependence of the stopping power is in qualitative agreement with the one derived from a one-dimensional shock model. Pressures estimated from the measured stopping power using the model are hundreds of megabars. The results show evidence of the collective interaction that results possibly from ‘‘hydrodynamic’’ shock behavior in plasmas formed by the coherent collision of high-velocity biopolymer atoms with target atoms.