The electronic pulses generated in the phototubes at each end of a scintillator cell must be reconstructed through a combination of electronic hardware and data aquisition software. The electronics serves the primary purpose of defining a valid event and its type. There are six main events processed by the electronics: 1) neutron-neutron (NN), 2) neutron-proton (NP), 3) proton-proton (PP), 4) single neutron hits (SINGLE), 5) cosmic rays (COSMIC), and 6) proton monitor events. The calibration events, PP and COSMIC were described above. For the data events, NN, NP, and NSING the electronics will determine their validity based on which combination of the 6 planes experienced a hit. The NN and NP have already been described. The NSING is a single hit in either the `analyzer' or the `catcher' without a hit in the charged particle veto paddles. The NSING data are generally only used during set-up when a high count rate is desired, since it is useless for polarimetry (which requires detection of the second scattering), and its count rate is heavily suppressed during the actual experiment. The proton monitor signal was mentioned in section and adds an uncorrelated data stream pertaining to the beam quality to the data from the neutron polarimeter.
The signals from the phototubes are split off twice before being used in the electronics as described above. A diagram is shown in figure .
Figure: Front-end electronics for a single neutron cell (CFD is a constant fraction discriminator).
One of these signals is attenuated and sent to a FERA ADC which will integrate the pulse-height information from the phototube. The other signal is sent, via a constant fraction discriminator (CFD), to a FERA TDC which produces timing information by producing a constant current during a window delineated by a common start and the arrival of the signal from the CFD. The signal produced by the TDC is sent to another FERA ADC. When the electronics determine a valid event has occurred it triggers a FERA driver to read the FERA ADC modules via a front bus. The FERA driver is then read on an event-by-event basis by VME hardware with an MC68040 Motorola microprocessor. This bypasses the typical use of the CAMAC memory buffer. The data is then transferred, using standard TCP/IP protocol, to a back-end computer, a VAX station 4000-90. This VAX station runs XSYS, which is IUCF's standard data acquisition and analysis software, to record and analyze the data. Using this set up the INPOL facility can take data at events/s with a live time (percent of time gathering data that is processed) of %, with a 10% fraction analyzed. This represents approximately an order of magnitude improvement over the speed at which the detector acquired data when it was at Los Alamos (NTOF). Fraction analyzed is the fraction of data fully analyzed online. The remainder of the raw data is written to disk and tape for later offline processing.