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    User name D. Parno / G. Franklin

    Log entry time 16:03:01 on February28,2009

    Entry number 263885

    keyword=Rate-Dependent Gain Shifts in Compton Photon Detector

    After swapping in a new tube base (the Mark V) for the GSO crystal (Compton photon detector), Gregg and I explored gain shifts in the detector signal. As the beam current was ramped up at 4-pass, we watched the Compton edge move as the rates increased.

    The plots below show the location of the FADC's Compton edge (as measured from amplitude in Fig. 1 and area in Fig. 2), plotted against the rates seen by the photon detector. (These rates are now measured in a scaler in the same VME crate; the threshold for an event to count is -50 mV.)

    Going from the one extreme to the other, we see a 22% increase in the Compton edge location (in raw ADC units) corresponding to a 680% increase in the photon detector rates.

    (Cross-posted to HAPLOG.)

    FIGURE 1

    FIGURE 2