The lifetimes of positrons annihilating in solids at the surface or close to the surface are measured by a pulsed positron beam of variable energy. A time resolution of 240 ps FWHM at a coincidence count rate of 70 s−1 is obtained. For stainless steel and nickel the lifetime associated to the annihilation in surface states is of the order of 500 ps. The lifetimes for the annihilation in trapping centers close to the surface are in complete agreement with the lifetimes observed in conventional lifetime measurements.
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Schödlbauer et al. (1987) studied this question.
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