Photoejection of both electrons from the H" ion by a single incident photon has been observed with use of a crossed-relativistic-beam technique. The dipole selection rules for a single photon pick out the i P° final state. The relative cross section was measured over a 0.30-eV range of photon energies near threshold in steps of 0.007 eV with a resolution of 0.007 eV full width at half maximum. The energy dependence of the cross section in this region was consistent with a Wannier threshold law.

A search for bursts of air-shower events from Hercules X-l at energies above 50 TeV during the calendar period 2 April 1986 to 5 July 1987 yielded two significant bursts, both occurring on UT 24 July 1986. The events during these bursts were pulsed with a period of 1.235 68 s, significantly different from estimates of the contemporaneous x-ray period. The probability that this represents random statistical fluctuations of the background is estimated to be 2xl0~5. The muon content of the burst events is anomalous when compared with expectations from 7-ray showers.PACS numbers: 97.80. Jp, 95.85.Qx, 97.60.Gb, 98.60.Df

We observe the Stark effect in hydrogen by photoionizing a relativistic hydrogen beam prepared by photodetachment of the 800-MeV H~ beam at the Clinton P. Anderson Meson Physics Facility. Photoexcitation of H° is performed in a magnetic field (up to 6.5 kG) that appears in the atomic frame as an electric field up to 3 MV/cm. Resonances observed with an angle Doppler-tuned laser beam match calculated energies. At sufficiently high field, near the Stark-Coulomb potential-barrier peak, we observe shape resonances with an apparent elevation of the base line on the high-energy side.

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