In August, because QTOR was off, the scanner was behind the pre-radiator, and there was a high threshold on each of two PMTs that were in coincidence, I assumed scanner triggers were generated by an infrequent hard gamma component (100's of MeV) from the front end that was showering in the pre-radiator. That may still be the case, but since Wilbur is a decent sized, single scintillator, I wouldn't rule out diffuse room background as the source of triggers. We seem to have no problem making background-biased triggers. Making an elastic signal-biased trigger with a nontrivial raster size is the challenge.
For signal biased electron triggers later in the program, we need a target, QTOR on, and Wilbur behind the pre-radiator in the elastic envelope (possibly with a high threshold). So everything may be in place. If Wilbur still sees too much background to take clean "signal" pictures with an 8x8 raster, John can duct-tape an inelegant pre-radiator to the front of the quartz scanner.