Significant fluctuations of energy loss are expected in certain cases of the passage of fast heavy charged particles through thin absorbers. When the number of particle-electron collisions in the upper collision-loss interval is small, the energy-loss distribution is asymmetric and is characterized by a broad peak around the most probable energy loss (which is significantly less than the mean energy loss) and by a high-energy-loss tail. Several theories predict the energy-loss distribution function, but previous experimental work is incomplete with respect to verification of theory over the whole significant range of the parameters involved. We have passed beams of 730- and 45-MeV protons, 910-MeV helium ions, and 370-MeV ${\pi }^{-}$ mesons through lithium-drifted silicon $p-i-n$ detectors and silicon $p-n$ junction detectors with depletion layers from 0.0085 to 1.094 g/${\mathrm{cm}}^2$, and measured the resulting energy-loss distributions. Within the limits of experimental error, there is very good agreement between the measured energy-loss distributions and those predicted by Vavilov's theory, and good agreement on the value of the most probable energy loss.

• Received 25 August 1967

DOI:https://doi.org/10.1103/PhysRev.165.469