Date: Fri, 16 Apr 2004 09:47:13 -0700 (PDT)
From: William Bugg
Subject: Re: CsI data


Achim,thanks for the information. Steve and I took some data with 30
GeV e164  beam on March 28 with high backgrounds. As you did we saw rather
steady backgrounds with variations of 10-20 %. Of course we have no way of
 knowing how similar conditions were to Feb 23 but I suspect they were not
too different. So for what it is worth GCAL sees about 20 TeV/cm2 directly
in front of your detector but upstream of all the shielding.  Your numbers
indicate about 1-2 GeV/cm2 (I assume 4cm square crystals)so the shielding
in front gives us reduction factor of order of 10,000.
I agree that these are not single particles of near beam energy as our
number would require almost 1000 of them per cm2 which is not likely.
It is of course possible that our data are not comparable because of
different run conditions. E164 had some upstream foils in the beam line
which were
giving us large signals in PCAL and may have increased the background. I
dont know if your runs had these foils inserted or not.
We also have some scope data taken from e165 running in the fall
which may
be a little better. We saw about a factor of 100 less background in
GCAL but the beam intensity was about a factor of 10 lower.

I believe that since our DAQ is up and working (with reasonably calibrated
detectors)it would be useful if we can talk our SLAC colleagues into
running the DAQ for us to get some data with all detectors running at
once.
The preparatory work needed is not extensive. We need to turn all the
detectors on and leave them on with the correct voltages. I believe
there is no risk in leaving them on all the time. I dont think this
presents any risk for the CsI and the silicon detectors have been on since
September anyway. We have not yet sucessfully gotten the offsite RUNDAQ to
work but thanks to Zen I think we are close so we could run the
system ourselves from our home base. Attenuators have to be used to get
signals in proper range for ADC.
Attached is an excel file showing data from silicon detectors in March 28
run.Nothing earthshaking here, just data from a 300 event run in various
counters with some figures showing correlations.
Cheers,
 Bill
We might eventually be able to sneak in some studies of the source of
backgrounds by moving silicon counters and shielding them. (with proper
permission from Radiation Rafety of course)



n Thu, 8 Apr 2004, Achim Stahl wrote:

>
>  Hi Bill,
>
> we habe taken data throughout the day on February, 23. We saw an almost
> monoenergetic peak in the crystals with a width of about 10%. We checked
> the signals on the scope and I'm 99% sure that these are real signals and
> not some electronics pick-up.
> The central energy of the peak was stable over short times, but it jumped
> every few minutes by up to 10% or 20%. It was early running after the
> shut-down and the machine people were tuning the beam. In some cases we
> could correlate the jumps with changes on the video display of the beam
> in 407.
> A typical energy of the peak was 20 GeV / bunch. The electronics goes into
> saturation at 23 GeV and it did so in some situation. Thererfore I don't
> really know what the maximum energy was. The peak was never below 15 GeV.
>
> Beam energy was 25 GeV, but I think this is not a single 25 GeV electron
> causing the signal, but a large number of low energy particles. Otherwise
> it would be hard to explain, why it was so stable. (We were running with
> beam trigger. There were no bunch crossings with no signal and also no
> bunch crossings with twice the signal (overflows).)
>
> It is not clear that the signal came from the front. Actually the
> shielding from the front was much thicker than the shielding from the
> sides, the back, top and bottom. Vinod took pictures of the setup
> --> http://www.slac.stanford.edu/~vinod/FFTB%20Feb%2004/
> Number 138 gives a good overview.
> Originally the idea was, to find out where the background came from,
> by changing the thickness of the shielding in appropriate places.
> But the background was so high, that we gave up.
>
>                                               Achim
>
>
> On Wed, 7 Apr 2004, William Bugg wrote:
>
> > Achim, my request for data on the phone today was really a very crude one.
> > I have measured with the Silicon counters  the energy/sqcm observed in our
> > area which is directly in front of your counters for typical beam
> > intensities in E165,E164 and SPSS running. The numbers are good to better
> > than 20% and are pretty constant for each experiment. If you have data
> > that tells us energy/sqcm inside your cave it would help me at least to
> > get a rough feel for how the shielding as it exists is improving the
> > background. So I really dont need data but just a rough number about
> > energy you see in a crystal.
> > Thanks, Bill
> >
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