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Efficient emission of positronium negative ions from Cs deposited W(100) surface has been observed. The emission efficiency measured over a time interval of 3000 s immediately after the deposition was found to be 1.25% for the target with a 2.2 × 1014 atoms/cm2 Cs layer. The emission from Cs deposited polycrystalline Fe surface has also been observed. The upper limit of the binding energy of the ion has been estimated experimentally. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Recently, we have observed spontaneous emission of positronium negative ions from polycrystalline tungsten surface. In the present work, we have extended the study to the emission from tungsten single crystal. The emission from tungsten (100) surface plane has been confirmed. The fraction of positrons yielding the ions at the target surface was ()4102.02.1−×±.