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Re: FCAL test
On Sun, 16 Sep 2007, Matthew Shepherd wrote:
Dear Matt,
I'm not completely sure I can exactly follow your argument.
If I have bigger blocks like the ones from Hermes 9*9*45cm^3 I contain
more of the shower in one block, I need to take this into account in my shower
algorithm, but that should be possible. Do I miss something.
What I think, has to be studied careful is that more radiation hard
lead glass has a different photon threshold, so could actually influence
the homogeneity of the acceptance.
Actually Beni, what did you calculate from the radphi data how many days
does it need till the blocks are completely blind. Of course all of this
has to be folded with the phase space of photons from pi0 we are
interested in. May be all of this is not a serious problem as the dose
should drop with 1/r. But I think we really want to look into more detail
in this, because it means we have an energy dependent gain, this can in
principle be calibrated out if you have a gain monitoring system along the
length of the blocks and with different wave length. But that is a
complicated one and gain monitoring systems which measure absolute are
very very complicated and expensive.
Matt could we put the whole thematics on one of the next calorimeter
meetings.
cheers elke
> Date: Sun, 16 Sep 2007 10:37:12 -0400
> From: Matthew Shepherd <mashephe@indiana.edu>
> To: Elke-Caroline Aschenauer <elke@jlab.org>
> Cc: Richard Jones <richard.t.jones@uconn.edu>, Elton Smith <elton@jlab.org>,
> beni zihlmann <bzihlman@indiana.edu>, Alex Dzierba <dzierba@indiana.edu>,
> Elliott Wolin <wolin@jlab.org>, George Lolos <George.Lolos@uregina.ca>,
> Zisis Papandreou <zisis@uregina.ca>, David Lawrence <davidl@jlab.org>,
> halld-cal@jlab.org
> Subject: Re: FCAL test
>
>
> On Sep 15, 2007, at 11:07 AM, Elke-Caroline Aschenauer wrote:
>
> > I have also the following questions. how critical is the size of the
> > crystals, could we look in getting some radiation hard crystals from
> > Hermes just for the center of the fcal.
>
> Size is critical to get the tight packing fraction. I think we
> almost need to tackle this from a physics standpoint. If I remember
> right the radiation does drops of exponentially as one moves to
> larger radius. (This is not dose, but rate and gives you some
> idead: http://www.jlab.org/Hall-D/software/wiki/index.php/
> FCAL_Backgrounds) This could mean only the blocks within 2 blocks of
> the beam hole get a hefty dose. If this is the case, can we live
> with damaged blocks in that radius? If we try to do something fancy
> just for those blocks then we create a boundary in the calorimeter
> there. The problem is that then no shower in that region is
> contained in blocks of one type or other. In addition alternate size
> blocks or some support that allows removal of central blocks would
> likely result in dead space between the blocks, which would be hard
> to deal with in reconstruction. Certainly we need to do some
> thinking and simulation, but it is quite possible that lesser of all
> evils is just to leave with radiation damaged blocks near the beam.
> I think the one exception to this might be if one could get rad-hard
> blocks that are exactly the same size at the blocks we have, but then
> we would still have a boundary and "hybrid showers." We just need to
> be careful that our rad-hard solution doesn't generate an effective
> hole in the calorimeter larger than we would have if we just let the
> inner blocks degrade.
>
> -Matt
>
>
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