On shift: Bill Franklin, Townsend Zwart
Compton polarimeter commissioning continued. Prior to the shift, Tavi
turned off HV for scintillators other than those which are part of the
polarimeter. Wire chamber HV was left on as requested.
We began the night working to generate more energy spectra. We kept the
beam current to 30 mA or less throughout the shift. With such currents,
signal-to-background in the energy region near the Compton edge was found
to be quite good (at least 5:1). We then turned our attention to
documenting event rates as a function of beam current, vacuum, and
collimator position. During a short access it was found that the
backscattered photon path was partially obstructed by a lead brick which
had served as a collimator during the previous run. This necessitated
repetition of a few previous scans, in particular the optimal collimator
position. We also tried using the halo scrapers for the first time. It
was found that these did not reduce background significantly for the
polarimeter, a finding consistent with the hypoothesis that nearly all of
our background comes from bremsstrahlung.
Tomorrow night, we will continue rate studies and optimized the
calorimeter gain before proceeding to examine the effect of inserting
absorbers into the backscatter line.
-- ********************************************************************** Wilbur A. Franklin * Phone: 617-253-9518 Bates Linear Accelerator Center * FAX: 617-253-9599 P.O. Box 846 * Email: wafrankl@mit.edu Middleton, MA 01949 * **********************************************************************
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