Nanosecond Time-of-Flight Studies of Electrons

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.