Secondary Emission from Mo Due to Bombardment by High Speed Positive Ions of The Alkali Metals

Work has been extended to measurements on secondary emission from Mo due to the bombardment of positive ions of ${\mathrm{Na}}^{+}$, ${\mathrm{Rb}}^{+}$ and ${\mathrm{Cs}}^{+}$ following the method used for ${\mathrm{K}}^{+}$ and described in detail in a previous paper. Confirmatory evidence is obtained that heat treatment in general reduced the secondary emission. With degassed targets the following results were obtained: ${\mathrm{Na}}^{+}$ ions showed a positive ion reflection of 3 percent or 4 percent independent of the speed of the impacting ion and electron emission of about 2 percent at 1000 volts. Experiments with ${\mathrm{Rb}}^{+}$ indicated a reflection of positive ions of less than 2 percent and no electron emission within the experimental error. ${\mathrm{Cs}}^{+}$ gave a secondary emission of about 9 percent at 1000 volts. It is suggested that the relatively large secondary emission from an untreated target as compared with a well degassed metal is possibly due to the minimum distance of the electron from the metal surface being greater in the former than in the latter case; also if secondary emission is due to local high temperatures arising from positive ion bombardment there would be more rapid dissipation of energy by the target surface than by the gas molecules.