Hi,
I've attached a very preliminary draft response to the NuSAG question $9,
dealing with calibrations and the movement of the detectors.  Please send
comments, thoughts, suggestions, etc.  It isn't very quantitative, but we may be
able to use some of the simulation results to beef it up.  The bottom line is that we
don't have to worry about things being constant, since we will measure and
re-measure everything anyway.  The one place this might not be true is for the
volume and the distribution of the Gd---we need to think about that a little bit.

      Thanks,
 Josh

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\section{What must remain constant?}

 Cross-calibration of the detectors by moving them is intended as a
bottom-line test of Braidwood's entire data acquisition, calibration, and
analysis chain. The requirements for constancy of detector parameters is minimal,
however, because nearly all the parameters will be re-measured before and after
any move.

The most important part of the detector which must remain the same is
therefore the calibration system itself, in particular its geometry and its 
positioning accuracy, as these can affect the calibration we will do at each position.  
Even here, however, we will be able to check for changes in the system, for example
by comparing the expected point at which a source just touches the inner
vessel to the point when it actually does.  We are not concerned with changes in the
calibration sources themselves, as these can be moved from one detector to another at
any time.  We outline below the calibration plans for the various configurations.


\subsection{Two Modules Near Site (Initial Running)}

 We will use the initial configuration, in which two modules are both
installed in the near site,  to shakedown and commission the detectors as
well as to understand the relationship between the detector parameters
(attenuation and scattering lengths, PMT gains, electronics channel 
efficiencies, neutron capture efficiencies, etc.) and the overall detection 
efficiency.  During this time, we will use both the embedded optical sources 
(LEDs on the outer sphere) as well as the calibration system itself to 
deploy $\gamma$, electron, neutron, and optical sources
throughout the volumes (the same radioactive sources can be deployed in
both detectors).  The goal of these source deployments is to build a complete
detector model which will allow us to predict the relative detector efficiencies
to much better than 1\%, and to verify that our model also correctly predicts the
dependence of the relative efficiency on any parameters which might change during
the move to the far location.  At the end of this initial period we will understand
the sources of difference (if any) in the response of the two detectors, and the
bottom-line test of this will be in comparing the antineutrino fluxes measured by
each detector.


\subsection{Two Modules Near, Two Far}

 In the second configuration, in which one of the near detectors has
 been moved to the far location and an additional module added to both the near
and far locations, we will begin by re-calibrating the moved detector and
comparing its parameters to those we measured at the near location.  These calibrations
will include measurements of the optical parameters (embedded LEDs and diffuse
deployed source), PMT gains and channel efficiencies (LED's and deployed
source), neutron capture efficiency (AmBe source), the overall energy
scale of the detector (AmBe and elecron source), and the volume of the
scintillator (direct measurement).  With these parameters we will then update our
detector model and predict what the relative response and efficiency of the
detector is after the move.  We will test our prediction by moving one or more
radioactive sources between the near and far detectors.

 During this stage, we will also perform the same comparison between
the two modules at each location as we did in the initial configuration.
Again, we will be measuring the detector parameters upon which our model
depends, and comparing the prediction to radioactive source runs in each
detector.  The final comparison will be the measurements of the neutrino
fluxes between each of the modules at the same location---they should
agree to well within the systematic uncertainties derived from the calibration.

\subsection{Swapping of Two Modules}

 The final and most critical move will be the last.  After movement
 and recalibration, we should be able to predict precisely what we expect the
moved detectors to measure relative to the ones which have remained stationary.