Re: FCAL test

[Matthew Shepherd <mashephe@indiana.edu>]

Hi Richard,

Yes, I agree with that scaling argument.  My statement was that as  
one then moves outward away from the beam hole on the array, the dose  
in each block should drop about like 1/r^3.  Where r is the radius in  
cylindrical coordinates of the block in question.

However, how certain are we that we can take RadPhi an directly apply  
this type of scaling argument?  Issues that come to mind are:

- all backgrounds are not produced at the target
- charged particle backgrounds (gamma -> e+e-) behave differently due  
to magnetic field

Do we have a geant model of the RadPhi beamline that we could compare  
with the GlueX simulations to try to explore these issues?

Matt

On Sep 17, 2007, at 5:01 PM, Richard Jones wrote:

> Matt,
>
> Someone should do a rough scaling argument here.  The Radphi hole  
> was 3x3.  The detector was 1.02m from the target.  Even if we keep  
> the hole size the same at 3x3, moving it downstream with rate ~ 1/ 
> r^3 means that the rate scales like distance from the target (3  
> powers for decreased angle - 2 powers for decreased solid angle = 1  
> power of distance): we should have a factor 6 worse exposure rate  
> in gluex than we had in Radphi for the blocks around the beam hole,  
> at the same beam intensity.  As I recall, gluex at 10^8 is the same  
> as the Radphi normal running intensity, within 30%, as far as beam  
> bg is concerned.
>
> Richard J.
>
> Matthew Shepherd wrote:
>> Why?  If I remember from Richard, the angular dependence is like 1/ 
>> theta^3 which corresponds to basically 1/r^3.  You can look at the  
>> plot -- remember it is a logarithmic scale.
>