LAB6/CEBIX MATERIAL SELECTION
The most important part of any thermionic cathode is the quality of the emitter material. We have over 20 years of experience in the growth and fabrication of refractory and boride single crystals. The exact composition of the cathode material has a dramatic effect on its evaporation rate and its efficiency in emitting electrons (work function). We have optimized the material composition (stoichiometry of B/La) for the highest possible ratio of electron emission to evaporation rate.

The evaporation rate of LaB₆ depends on the electron column pressure and cathode temperature. If the LaB₆ gun operating temperature is 1800K with a pressure at the emitter of 5 x 10^-7 torr, the evaporation rate is about 36nm per hour, or 1400 hours for 50 micrometers of evaporation and 2800 hours for 100 micrometers of evaporation.

At 2x10^-8 torr and 1800 K, the evaporation rate of CeBix is about 30% lower than that of LaB₆; therefore, the expected lifetime of CeBix under these conditions is about 30% longer than LaB₆.