[Halld-pid] ADC

[Mark M. Ito]

Sasha,

I checked your arithmetic and I agree with your numbers (see attached 
spreadsheet). If we assume minimum ionizing particles at normal 
incidence, I get 440 photoelectons per MeV. I don't think that that is 
so unreasonable.

   -- Mark

On 10/03/2011 10:06 PM, Alexander Ostrovidov wrote:
> 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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