[Halld-pid] ADC

[Alexander Ostrovidov]

Beni,

OK, here is an estimate for the number of
photoelectrons from a minimum ionizing peak
for a hit in the middle of a TOF paddle:

1) Peak of Landau distribution is at 890 ADC counts,
pedestal is at 350 counts. With 0.25 pC per ADC count,
the integrated charge is (890-350)*0.25 pC = 135 pC

2) There is exactly factor of 4 loss due to a 50-50 splitter
and 50 Ohm terminator at the PMT. This was verified
with a pulser. This results in 135 pC * 4=540 pC at
the anode.

3) Therefore, the number of electrons at the anode is
540e-12 / 1.602176565e-19 = 3370415045

4) PMT has a gain of 1.576e6 at 1750V. So, the number
of photoelectrons from a single hit is
 3370415045 / 1.576e6 = 2138

Sasha

On Friday, September 30, 2011, Beni Zihlmann wrote:
> Hi Sasha,
> thanks for the info.
> the cable length should not matter if the ADC gate is
> sufficiently long.
> 
> cheers,
> Beni
> > On Friday, September 30, 2011, Beni Zihlmann wrote:
> >> Hi Sasha,
> >> in the link
> >> https://halldweb1.jlab.org/talks/2011-3Q/ADC%20spectra%20and%20Time-walk%20corrections_files/
> >> you show an ADC spectrum of a paddle PMT: adc_l_par_nottrig.gif.
> >> what is the HV of the PMT set at and what type of ADC are you using?
> >>
> >> cheers,
> >> Beni
> >> _______________________________________________
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> >>
> >>
> > Beni,
> >
> > This particular plot is done with:
> >
> > 1) CAEN ADC v265 in 12-bit mode. This  corresponds to
> > 0.25 pC per count
> >
> > 2) 10-stage PMT with a nominal gain of 1.5*10^6 (at 1750 V).
> > However, it was used at 2000 V in this particular measurement.
> > So, its actual gain is unknown in this case.
> >
> > 3) What makes things more complications is a signal attenuation
> > on its way from PMT anode to the ADC due to a 50-50 splitter,
> > a 50 Ohm terminator right at the PMT,  and 150ft of cable. Right now,
> > I'm trying to measure what is the correction coefficient I need to apply
> > to compensate for this attenuation. I should have an estimate of the
> > number of photoelectrons later today.
> >
> > Sasha
> >
> >
> >
> >
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> 
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