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We report experiments in which radiatively metastable 2 3 S 1 $2\,^{3}\mathrm {S}_{1}$ positronium (Ps) atoms entered a waveguide whose internal surfaces were lined with smoked magnesium oxide (MgO) powder. The waveguide was built such that time-delayed microwave radiation pulses, tuned to drive 2 3 S 1 → 2 3 P 2 $2\,^{3}\mathrm {S}_{1}\rightarrow 2\,^{3}\mathrm {P}_{2}$ transitions, could be applied to the Ps ensemble. The lifetime of 2 3 S 1 $2\,^{3}\mathrm {S}_{1}$ atoms was measured using time-delayed microwave induced decay, yielding ≈200 ns. This is considerably shorter than the Zeeman shifted lifetime of 1070 ns, indicating that Ps atoms in the 2 3 S 1 $2\,^{3}\mathrm {S}_{1}$ state do not survive multiple collisions with MgO nanocrystals.

Fast decay of 23S1 positronium atoms in an MgO lined cavity