Question 9 comments

From: Hans Jostlein (
Date: Thu Jun 30 2005 - 13:29:50 CDT

Sorry for the last minute responsae-- I was buried.

Here goes:

My comments:

we are not taking appropriate credit for cross calibration at the end:
Clearly we start with two detectors normalized to one another at the near
Then we move one and track its parameters using all sorts of calibrations.
It is important to bring those two detectors back together at a later time
to verify that the tracking has been successful.
This is not unlike surveying magnets in the Tevatron and then closing the
loop to where one began.
This improves the accuracy hugely and is really the only experimental way to
put a number on the accuracy of tracking parameters.

After the very first sentence add something like:
"A second cross-calibration near the end of the experiments will both
examine the success
of the ccalibration system in tracking detector responses and
reduce the uncertainties in the tracking process by having firm data at the
beginning and at the end of the run."

a. We are much too specific about deploying an articulated source
throughout the volume with 2 cm accuracy.
I don't think we want to commit and to "baseline" this device.
There are good reasons not to:

First of all, if the positioning accuracy is 2 cm, then the volume
uncertainty, even for perfect measuremsnts,
 we will only calibrrate at the level of (6cm/350 cm) which is at the 1.7 %
. This is not at all useful.

Secondly, the presence of the mechanism and the source holder changes the
local materials distribution,
presumably also at least at the 1% level (needs detailed work)

Thirdly, the requirement for a 3 ft opening at the top makes the detector
highly anisotropic.
This is a big concern, since the neutrino wind changes form 45 degrees at
the near location to 6 degrees from the horizontal at the far location.
I imagine one could get around this by tilting the detectors at 19.5 degrees
in opposite directions at the two sites,
but that has huge engineering and cost consequences.
I cannot tell at what level the 3 ft diameter "special place, without
PMT's" at the North pole creates near / far differences, but it is not a
comforting thought.

Alternatively, if one can get by with a source/ LED device that scans only
along the detector vertical axis,
this can be done through a small (1/2 inch or so) opening at the top.
I have a conceptual design for that.
It can be done with superb accuracy (about 1 mm) at any point along the
axis and it is simple and robust enough to run automatically and frequently.
It requires no modifcations to the sphere at all.
This device can also easily and accurately (1 mm) detect when it hits the
bottom of the sphere and when it emerges from the oil at the top.
Response as a function of distance from the acrylic can be mapped out in
exquisite detail (along the axis only, though)

Bottom line: I suggest we delete all references to this articulated source,
e.g. "by deploying sources near the edges of the active volume . ."

b. Under 9.1, a quibble:
we have "change in the effective number . .", followed by " "appear to be a
loss of efficiency . ."
This could be a gain or a loss; we should express this self-consistently

c. Under 9.2.1,
the first sentence makes it sound like that changes in the PMT's and
associated electronics are likely.
I am confident that we will not see much change other than that of
temperatur changes (if they should occur), which would be fully reversible.
Change ":the most likely change . ." to:
We do not expect any significant non-reversible change or any PMT failure
during the moves. If any changes should occur, or PMT's be damaged, then
these can be easily determined . . ."

d. Under 9.2.1:
I would suggest to omit the sentence "Only catastrophically large changes .
We have no expectation or reason to believe that the occurrence of such
changes is credible.

e. Under 9.2.2
What exactly is " a diffuse optical source" ?
Do you mean many sources thorughout the volume (which I fully expect to
have, in several colors) or do you mean a moving source with an isotropic
optical emission?

f. Under 9.2.3 you say:
" . .therefore small changes can have a big effect .".
This is in contrast to our statement under 9.2.1 :
"We are very insensitive to changes in these efficiencies . . ."
Which is it ?

g. Under 9.2.4
I would suggest to omit the SNO anecdotal evidence, even though it is cute
and intriguing; it just doen't apply to Braidwood.

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