Wide-band detector for micro-microampere low-energy electron currents

Electrons with a mean energy of a few electron volts emerging from a source a few millimetres in diameter are accelerated on to a positively biased plastic scintillator. The light generated in the scintillator is guided by a Perspex light-pipe to a photomultiplier. If the scintillator bias is greater than 10 kV, no noise is introduced by the scintillator-light-pipe-photomultiplier system. If the original electron signal is modulated, the maximum modulation frequency transmitted by the system is greater than 10 Mc/s. The minimum detectable current is limited by the photomultiplier dark current, and may be less than 10 -15 A with a suitably chosen tube.