Fast Timing Circuits Using Storage Diodes

A constant-charge pulse shaper has been used as the basic element in two fast timing circuits using photomultipliers. The shaper is based on storage diodes (snap-off diodes) and delivers an approximately constant charge at the output, almost independent of the input current pulse amplitude. These constant-charge pulses are delivered to a tunnel diode, which in the sub-nanosecond range is a charge sensitive device. A coincidence circuit and a time-to-amplitude converter were built and operated with a Co60 source, two plastic scintillators used with 56 AVP tubes, and a slow coincidence discriminator. With a range of 20 mA to 200 mA the coincidence slope was 0.4 nsec for half-amplitude, while the time-to-amplitude converter showed a FWHM of 0.8 nsec on a multichannel analyzer.