The attached plots show 55Fe PH spectra from the PPP at various
applied high voltages.  I also took a few spectra where the ADC gate
width and/or the delay between the start of the gate and the leading
edge of most WC signals was varied.

    The spectra are "named" as follows:
    PVVVGGDD  where:
        VVV - (HV/10) in volts
        GG  - (adc gate width)/10 in ns
        DD - delay between gate and signal in ns

Most spectra were taken with gate width = 300 ns, and delay = 45 ns.
Shortening the gate below ~ 100 ns, and reducing the delay to ~ 0 had
effects similar to that shown in P1850800 below.  Increasing gate width
or delay above 300ns/45ns had no effect.

    At very low voltages there appears to be only one peak in the
spectrum.  As the voltage is increased a peak at higher PH appears.   As
the voltage is further increased, more and more counts fall into the
"high" peak as opposed to the "low" peak.
    The overall gain of the system was varied using the gain control on
the NIM spectroscopy amp, and an attenuator box.  To enable rough
comparisons between spectra, I have written the relative gain (varying
from 0.3 to 10) on each of the spectra.

    Iouri and I are working on an absolute calibration of the gas gain
in each case, so that a more careful study of what is happening can
occur.  It is possible that some kind of streamer mode is occuring.
Since the onset of the streamer mode is likely dependent on the density
of charge deposited in the WC, we need to do further studies to
understand what effects may occur with minimum ionizing electrons and
heavily ionizing muons.

                                            Robert

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Filename: P1850800.jpg

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