Electron detection system

Plastic scintillators, in addition to providing a charged particle veto for neutron and photon detection, were used to detect the electrons with an independent trigger, recording the electron time spectrum (Fig 3.25). Since statistics for the electron measurement were not a problem, the trigger was pre-scaled by factor of 4, in order to reduce the load on the data acquisition system.

  

Figure 3.25: Electronics diagram for the electron detection by plastic scintillators and the dynode output of the neutron detectors. Only scintillators in front of the neutron detector are shown here, but all other ones were also connetced to the logical OR module to give an electron trigger DELE. The neutron dynode output provided not only the timing of the electron, but also its energy.

This circuit also provided a tool called delayed electron (Del) coincidence for reduction of muon capture related background, where one demands that the muon-decay electron be detected after the reactions of interest, hence ensuring the muon was alive, (i.e., had not decayed nor been captured by) then. In case of nuclear muon capture, the muon was converted to its neutrino, and no electron would be observed in the delayed time window, which was typically from 0.2 to 5 $\mu$s after the reaction. For the Del concidence, the master trigger was always given by the detector of interest, therefore no pre-scaling of the signal was necessary.

The neutron detectors could also be used for electron detection by utilizing a fast signal from the dynode of the photo-multiplier. A separate trigger, called telescope or simply Tel trigger, was implemented which required a triple coincidence of two plastic scintillators and the dynode signal, with the latter energy also recorded.