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Thermionic emission measurements using pulse techniques have been obtained from UC-coated W filaments in the temperature range of 1200°–2100°K. From the slope and intercept of the Richardson plot, a value of φ=2.94 ev and A=33 amp/cm2 deg2 was indicated. There is evidence that the energy required for electrons to escape at low fields might be several tenths ev higher than the 2.94 ev value.
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Haas et al. (1960) studied this question.
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