Negative hydrogen ion emission from heated metal hydride powder

A small ion source (∼2 cm2) of the self-surface negative ionization (SSNI) type was developed to generate H- from a powdery sample (∼10 mg) deposited on a molybdenum ribbon (∼0.1 cm2). For example, CaH2 heated up to ∼900 K emitted ∼0.1 nA of H- together with ∼1 mA of thermal electrons. The work function of CaH2 was ∼6 to 5 eV, depending upon the history of its thermal processing. The introduction of H2 up to ∼10-4 Torr did not increase H-, indicating that the efficiency of producing H- by electron impact of H2 is much poorer than that by SSNI of CaH2. Emission of H- was also observed with LiH but not with NaH and ZrH2. copyright 1996 American Institute of Physics