Log entry time 11:58:32 on June29,2004

Entry number 127368

This entry is a followup to: 127362

   The window thickness for the 20 cm racetrack hydrogen cell
is 2 x 7 mils = 0.356 mm; the dummy cell is 2 x 1mm = 2 mm, so
the "xt" factor is 0.178, and thus Bob's online results indicate
an aluminum background of 0.7% to 0.9%.  Great!.

  Assuming a 10 ppm asymmetry from Al quasielastic (pure guesswork
on my part) means that if we measured that asymmetry to 10% (1 ppm)
we would have a systematic background correction of around 80 ppb,
with an error of about 15 ppb (adding errors on background fraction
and asymmetry in quadrature), which is very tolerable, for the full
statistics in the proposal. Of course we don't need quite this level
of precision for this run.

  However, at 35 µA on the dummy target (run 2527) the combined
4-detector width was about 2800 ppm; this means one would need 147
hours to get a 1 ppm asymmetry from the dummy cell - ugh!

  Do we need (for next year) a thicker dummy cell? How much current
could we run on the dummy cell?