The luminous events produced by a drifting relativistic electron beam (REB) (1–2 MeV, 100 kA, 40 nsec) have been photographed with an image converter of 5‐nsec gate time. Coupled with a transmission spectrograph, time‐gated snapshots (1 mgr;sec) of the spectra have been recorded. For air pressure between 0.1 and 0.3 Torr, the beam is self‐focused and it yields a spark spectrum containing mainly N+, with some O+and N++lines. In 0.8–1 Torr of air, the beam is unfocused and it yields the N2(B←C) but not the (A←B) bands. In the presence of a target, the unfocused beam may again produce an air breakdown. A slitless spectrum then yields a two‐dimensional image of the event, which may be related to the spatial distribution of the beam. The results are discussed in connection with REB and ion acceleration research. In addition, Lichtenberg‐type discharge tracks in a Plexiglas disk irradiated by 2‐MeV beams are photographed and compared with the fluorescence lifetime of the N2(B←C) bands.
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