Electronic stopping cross sections for ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ projectiles (840-175 keV) have been measured with the inverted Doppler-shift attenuation method in liquid ethane (${\mathrm{C}}_2$${\mathrm{H}}_6$) at two different densities. The density of the target has been varied by changing the temperature, and measurements have been performed at 0.525 g/${\mathrm{cm}}^3$ (199 K) and 0.362 g/${\mathrm{cm}}^3$ (287 K). At the higher density the stopping cross section is about 2% smaller. This result agrees with a calculation of the stopping cross section of liquid ethane, applying Lindhard's theory in the local-density approximation using a simple model of the liquid. It is also in agreement with various observations of the so-called physical-state effect, which show that the stopping cross section of the same substance is smaller in a condensed phase than in the gaseous one.

• Received 6 June 1983

DOI:https://doi.org/10.1103/PhysRevA.28.3212