Re: updated geometry

[Beni Zihlmann <zihlmann@jlab.org>]

Hi All,
talking to Elton I think this issue with the Aluminum plate is more tricky.
Here is the deal.
The 8mm Aluminum are supposed to replace the first 0.5mm lead of the 
lead/scintillator
matrix. So after the last scintillator layer this aluminum plate is 
glued on instead of a lead
layer with the aluminum being so thick that it is equivalent to the last 
layer of lead. That is
where the 8mm thickness is coming from.
This means I have a problem modeling this in the geometry file because 
the active volume
of the calorimeter is already defined as a mixture of 
lead/glue/scintillator. So I can not simply
replace the innermost 0.5mm lead by 8mm aluminum.

My conclusion of this problem is that we should leave it as it is 
without aluminum plate
for the simulation because this is the closest to reality in terms of 
radiation length and that
is probably more important/critical than the additional volume size.

What is your opinion?

cheers,
Beni

> Hi Elton,
> ok but then I think what I did is wrong. I just added the Aluminum 
> plate to the existing
> BCAL geometry. That means the total thickness increased by 8mm.
> From your comment I take it that the calorimeter should go in radius 
> from 65cm to 90cm
> this corresponds to a total thickness of 25cm with the first 8mm  
> Aluminum and the last 2.54cm  Aluminum.
> Do I understand this correct?
>
> cheeres,
> Beni
>> HI Beni and Richard,
>>
>> I am entering this discussion mid-way, but the Al plate was to 
>> replace the
>> first lead sheet and it has a similar number of radiation lengths. So 
>> the
>> effect on low-energy photons should not be too different than the 
>> original
>> design.
>>
>> Cheers, Elton.
>>
>>
>>
>>
>> Elton Smith
>> Jefferson Lab MS 12H5
>> 12000 Jefferson Ave
>> Suite # 16
>> Newport News, VA 23606
>> elton@jlab.org
>> (757) 269-7625
>> (757) 269-6331 fax
>>
>> On Mon, 14 Jul 2008, Richard Jones wrote:
>>
>>  
>>> Beni,
>>>
>>> Yes we should have as much of reality as is relevant for performance,
>>> and certainly this plate will affect the performance.  But it simply
>>> cannot be there if we want to measure low-energy photons.  Perhaps we
>>> can let the MC studies show that, but I don't think we need MC to know
>>> what the result will be.  I would say that our concern about the FDC
>>> cables pales in comparison with this.
>>>
>>> Richard Jones
>>>
>>> Beni Zihlmann wrote:
>>>    
>>>> Hi Richard and All,
>>>> indeed I forgot to adjust the overall module volume to accommodate for
>>>> the inside aluminum plate. I can/will fixt that in a second.  But now
>>>> I have a question to your comment. I agree that an 8mm aluminum plate
>>>> inside the BCAL surface will degrade the resolution but that is
>>>> exactly what is in the drawings to build the BCAL and Elke asked me to
>>>> put it into the geometry. Don't we want to have the studies to be made
>>>> by Matt et al. having a geometry as close as possible to reality?
>>>>
>>>> cheers,
>>>> Beni
>>>>
>>>> Btw. yes I am really interested in your tools.
>>>>
>>>>
>>>> Richard Jones wrote:
>>>>      
>>>>> Beni, some work is still needed on this geometry.  The following
>>>>> items are invalid, so that no particle will ever be able to enter
>>>>> their volumes.  This is not a comprehensive list, just the result of
>>>>> a quick spot check I did.  I have a tool that can enables a quick
>>>>> point-and-click check on individual volumes.  I can show you how to
>>>>> use it, if you are interested.
>>>>>
>>>>>    1. FDC cables re-routed to run upstream
>>>>>    2. 8mm aluminum plate in front of BCAL
>>>>>
>>>>> That aluminum 8mm plate will completely wipe out the BCal resolution,
>>>>> once it is in there!  For the moment, however, it causes no problems
>>>>> at all, because particles do not see it. :-)
>>>>>
>>>>> -Richard Jones
>>>>>
>>>>>
>>>>> Beni Zihlmann wrote:
>>>>>        
>>>>>> Dear colleagues,
>>>>>> I updated the geometry in the repository. The geometry now reflects
>>>>>> all the changes and design decisions that have been made lately.
>>>>>> 1) remove outer most CDC layer thereby reducing the CDC radius by
>>>>>> 1.6 cm
>>>>>>    including the cable runs.
>>>>>> 2) re-route the FDC cables to run upstream
>>>>>> 3) add an 8mm aluminum plate on the inside of the BCAL
>>>>>> 4) the BCAL readout segmentation is 4x6 (sector x layer)
>>>>>>
>>>>>> all these changes are now available the in geometry file
>>>>>> hddsGeant3.F located in
>>>>>> src/programs/Simulation/HDGeant/
>>>>>>
>>>>>> cheers,
>>>>>> Beni
>>>>>>
>>>>>>           
>>>>       
>>>     
>>
>>   
>
>


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Benedikt Zihlmann
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