[Moller_simulation] position of target in sims

[Cameron Clarke]

Juliette,

I agree with everything you have. I do not remember exactly why I put 4
meters as the Hall offset from the target position, but it is wrong.
Fortunately the effect of this 2 meter offset likely only extends to
miscounting hall wall-sourced rebound radiation and missing the edges of
the radiation that hits the roof. I will make a pull request with the new
number (so it gets logged in github more formally) that I obtain from
measuring exactly the placement of the pivot in the MOLLER CAD. The pivot
and spectrometers were placed by me into the SBU MOLLER CAD a few years ago
and is exactly *6087 mm* downstream from the target center defined origin.
I don't remember exactly what numbers I was using to place it with respect
to the target, but hopefully this number is correct, and it is certainly
better than 4 meters.

I'm sorry my placeholder simulation geometry files are causing confusion.
Another concern with them is the radius that is implemented. This radius
was wrong at one point and I updated it based on the CAD, and this may mean
that the height placement or the radius of curvature of the roof are not
correct as well (though this is less significant hopefully).

Thanks,
Cameron Clarke

On Fri, Nov 2, 2018 at 4:09 PM Juliette Mammei <crowder at jlab.org> wrote:

> Dear all,
>
> I believe that the target position in the simulation is incorrect.
> According to Robin's drawings, it looks like the target is at least 5 m
> upstream of the pivot/hall center, not 4 m, as I believe is in the
> current simulation.    I just talked with Jay and he tells me that in
> his layout the target center is indeed 6 m upstream of the pivot.  So I
> believe this is the correct value.
>
> For optics this is okay, because the spectrometers and detectors are
> placed relative to the target center.
>
> But for shielding design this could be a problem, because it has to be
> designed around the pivot and spectrometers.  I believe Wouter has
> discovered the resulting lack of space between the wall and the detector
> region.  There should be 2 more meters there, assuming Jay is correct.
>
> I have send an email to Robin to ask about the position in the CAD
> drawings that she has shown, and I am waiting for a response.
>
> Thanks,
>
> Juliette
>
> --
> Dr. Juliette Mammei
>
> Assistant Professor
> Department of Physics and Astronomy
> University of Manitoba
> Winnipeg, Manitoba
> R3T 2N2 Canada
>
> Office: 1-204-474-6195
>
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