Shift began with the installation of 1 layer of Mu metal on RTOFTOP15.
Two sheets were wrapped around the exterior of the PVC housing spanning
from the black split ring to within ~3cm of the base connectors. With
voltages set to +10% we saw the following behavior:
Field OFF:
RTOFTOP15 rate =~65Hz
RTOFBOT15 rate =~65Hz
Field ON:
RTOFTOP15 rate =~55Hz
RTOFBOT15 rate =~20Hz (unshielded)
So the extra Mu-metal does provide some shielding. However, as John
pointed out, we must adjust it so that it extends far enough beyond the
PMT boundaries so as to provide a more complete exclusion of the field.
The next main task of the night was to determine the cause of the peak
that appears in the adc spectra (~ch 900) upon raising the voltages by 5%.
RUN 2282 HV set to +10% to make peak obvious
RUN 2283 HV set to +10% with RTOF0 and LTOF0 voltages turned off
as they were suspected of being the source of the problem.
This made no difference and the peak was still dominant.
RUN 2284 raised thresholds on LTOFTOP1,2,3 from 31mV to 52mV
This made no difference and the peak was still dominant.
RUN 2287 raised thresholds on LTOFTOP1,2,3 from 52mV to 62mV
This made no difference and the peak was still dominant.
Also conducted analysis on these runs by asking for only those events
where two tdc's fired. The peak still remained even with this cut.
RUN 2288 raised thresholds on LTOFTOP1,2,3 from 62mV to 93mV
Only saw events above ch ~1100 so peak was essentially cut out.
****Did not want to gain match with this setup as the peak is near ch 1000
which is near the peak for adc spectra with standard voltage settings. It
is certainly NOT pedestal****
Started wondering if we were triggering on tube noise. Since no beam was
available and we saw a horizontal cosmic rate of about 3 or 4Hz we decided
to take a coincidence run to see if this would eliminate the peak.
Modified our cosmicTOF.settings so that we demanded LR coincidence in the
XMLU.
RUN 2289 Horizontal Coincidence (LTOFTOP1,2,3 still @ 93mV thresh all
others @ 31mV). There was no dominant spike seen in this run, but it was
possible that one was "forming" as we only had 13000 events.
Pete & Jason
----------------------------------------------
Pete Karpius
Graduate Research Assistant
Nuclear Physics Group
University of New Hampshire
phone: (603)862-1220
FAX: (603)862-2998
email: karpiusp@einstein.unh.edu
http://pubpages.unh.edu/~pkarpius/homepage.htm
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