The currents (J(-) and I-) of thermal electron (e(-)) and ion (H-) desorbed from heated powdery SrH2 were simultaneously measured by mass spectrometry as a function of the sample temperature, introduced H-2 gas pressure or time elapsing after increasing temperature, introducing H-2 or stopping the introduction. Analysis of the data thus obtained yields the notable results as follows. (1) Above similar to800 K, those active spots (Sr) with low work function (phi) is created by such a thermal decomposition as SrH2 --> Sr + H-2. (2) From the spots, not only e(-) but also H- is desorbed even without introducing H-2. (3) By introducing H-2 up to similar to5 x 10(-4) Torr, phi is increased by up to similar to0.3 eV according to a deactivation reaction (Sr + H-2 --> SrH2). (4) By this increase, J- is decreased to less than 1/10 but I-is increased up to similar to2.4 times. In conclusion, H- is thermally produced not only from the H constituent of powdery SrH2 kept above similar to800 K but also from the H-2 introduced onto the hydride, in spite of low electron affinity of hydrogen. (C) 2002 Elsevier Science B.V. All rights reserved.