The ionization efficiencies of the high work function metal sheets

such as Ta

Fe

W

Ni

Re and Pt ionizers

were studied and compared between them by calculating the degree of ionization and positive ion densities as well as measuring the target currents and negative ion beam intensities. It was shown that Fe as a kind of general metal

was also a better ionization material. The effects of surface temperature

pressure of cesium vapour and surface work function on the surface ionization process were also discussed.