Nanosecond Time-of-Flight Studies of Electrons

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Abstract
Low‐energy electron guns have been constructed in planar and coaxial geometry. When pulsed with nanosecond pulses from an avalanche transistor pulser, they emit bursts of electrons of a few nanoseconds duration having energies adjustable between 1 and 15 eV. Electrons are focused along a drift tube by a magnetic field of the order of 1 G and are collected and then amplified by a 3‐stage transistorized pulse amplifier for display on a sampling oscilloscope. For microsecond drift times an energy resolution of about 0.01 eV is calculated. The depletion of 2.5‐eV electrons in the time‐of‐arrival distribution when the pumping system was cut off from the drift tube was attributed to vibrational excitation of N2, and a cross section of 1.34×10−15 cm2 was determined. When the drift tube was re‐evacuated and a jet of nitrogen gas was directed across the electron beam at right angles to it and close to the gun, the time‐of‐arrival distribution revealed energy losses of 0.6 or 1.0 eV which were attributed to vibrational excitation of the v=0 to v=2 or v=3 levels in nitrogen. These experiments, plus work done in other laboratories on gating grid arrangements, seem to indicate that a time‐of‐flight electron monochromator having energy resolution comparable to the best systems in operation at this time may be possible in the future.