The practical range of low-energy electrons in thin ${\mathrm{Al}}_2$${\mathrm{O}}_3$ films has been measured. Films ranging in thickness from 85 to 5000 A were investigated. Results are in close agreement with the predictions of Bethe and the results obtained by Hoffman for 1000-3000 A ${\mathrm{Al}}_2$${\mathrm{O}}_3$ films. The practical range-energy relation obtained was found to be $R=0.0115\mathrm{}{E}^{1.35}$, where $R$ is expressed in mg/${\mathrm{cm}}^2$ and $E$ in kev.

• Received 11 April 1956

DOI:https://doi.org/10.1103/PhysRev.103.292