Phys. Rev. Lett. 46, 717–720 (1981)Observation of the Positronium Negative IonReceived 24 December 1980; published in the issue dated 16 March 1981 A beam of 400-eV positrons is partially transmitted through a 40-Å C film in vacuum. Measuring the γ-ray energy spectrum with a downstream Ge(Li) detector, a new γ-ray peak is observed, the energy of which can be changed by applying a voltage to a grid behind the film. Attributing the new peak to a Doppler-shifted annihilation γ implies a mass-to-charge ratio 3.011(14)m/e, thus signaling the presence of the e-e+e- positronium negative ion, Ps-. The Ps- conversion efficiency of the C film is (2.8±0.3)×10-4. © 1981 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevLett.46.717
DOI:
10.1103/PhysRevLett.46.717
PACS:
36.10.Dr, 03.65.Ge, 34.70.+e, 78.70.Bj
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