Interposer %2

[Yves Van Haarlem <yvhaarle@ernest.phys.cmu.edu>]

Hi Fernando,

The measurements we did using the new %2-interposer (which reduces the 
charge going into the preAmp by a factor of 2 are on the wiki:

http://www.jlab.org/Hall-D/software/wiki/index.php/Measuring_Fe-55_X-rays_with_%252_interposer_board

You can compare them with the spectra from GlueX-doc-1079. I am updating 
that document at the moment. The threshold was set as such that the rate 
was low enough so the VME computer did not crash.

Here's a quick analysis:
The mystery of the second peak remains, athough at 1900V it disappears. 
Most of the time the threshold is too high in order to see the 'real' 
escape peak. Comparing the spectra with the older ones at 1750V the "%2" 
Ar-peak has a mean value which is half the value of the previous Ar-peak. 
For higher HV this is not true anymore. Which probably means that the 
pre-amp is in a non-linear mode for higher HV using the old interposer. At 
1950-2000V we might be leaving the proportional and/or saturate the 
preAmp again (%2 interposer).

The sharp steps on the left side of the spectra is due to the threshold, 
the events before the threshold are due to the signal finding algorithm 
(it takes the first peak that is higher than 4\sigma as the signal).


Cheers,
 	Yves



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