Surface ionization negative ion source

A negative ion source that utilizes a porous lanthanum hexaboride surface to generate iodine ions is described. Iodine vapor supplied to the back of the lanthanum hexaboride ionizer from a reservoir percolates through to the front surface where the iodine is evaporated as ions. The peak ion current obtained—2.1 mA at an ion energy of 0.3 keV—leads to a density n≃1010 cm−3.