Re: pmt glass radiation--how big are the PMT's ?

From: Jonathan Link (
Date: Wed Jun 01 2005 - 09:40:08 CDT

Hi Hans,

The Hamamatsu catalog shows the tube plus its base. MiniBooNE used a
homebrew base that is flat and does not extend beyond the bottom of the


Hans Jostlein wrote:

>Thanks for the detailed and useful description, Matthew
>Meanwhile I have come across a much more mundane riddle.
>The display of the Miniboone tubes here on Wilson hall 10 has, indeed, the
>cathode at about 10 inches (254 mm) from the steel wall.
>However, if I look up the R5912 PMT in the Hamamatsu catalog,
>the drawing says that the tube itself is 290 mm tall, i.e. about 50 mm
>taller than the Miniboone tubes.
>What is the real story here?
>----- Original Message -----
>From: "Matthew Worcester" <>
>To: <>
>Sent: Tuesday, May 31, 2005 7:58 PM
>Subject: pmt glass radiation
>>Hi Mike et al,
>>Here is what I've learned about the pmt glass radiation from my MC
>>studies, in no particular order. With a 90 cm buffer the pmt face is
>>actually 25-30 cm inside the oil, so the reduction is not as much as you
>>might expect. The most important parents of high-energy gammas are
>>208,210Tl and 212,214Bi, which are in the U/Th chain. Hamamatsu quotes 10
>>decays/pmt/sec but won't give any further information.
>>So the simulation generates gammas from all 4 isotopes above with proper
>>BR and multiplicity, with one decay per event. It assumes pointlike PMTs
>>to generate from, and places them 30 cm inside the buffer. It has 935
>>pmts. The gammas compton scatter through the oil. Attached is a plot of
>>rate vs. thickness, which fits an exponential nicely. With the 90 cm
>>buffer you see about 5% of the events have at least 1 gamma compton
>>scatter inside the scint, for a rate of about 400 Hz.
>>The key to understanding the radiation is that most gammas that hit the
>>scint have already scattered away most of their energy. So the energy
>>from those gammas is buried in the pedestal noise. So the question,
>>which I don't have an answer to, is how often out of that 400 Hz does pmt
>>radiation fake a positron? Looking at the energy from the gammas (those
>>plots are in my May 13 software talk) I'm guessing it will only be about
>>1% of the time, for a 4 Hz fake e+ rate (almost all from the Tl).
>>We've measured the spectrum from a Hamamatsu R5912 tube at Chicago with a
>>Ge detector and seen the K,U, and Th peaks but have not converted that
>>into g/g yet. We are also getting a sample 8" pmt from Electron Tubes to
>>check its radiaiton.
>>I would not put any of these plots in your talk, but I think if you are
>>asked about it it's fair to say that we have a working simulation that we
>>are refining with pmt samples that we have received from several vendors.

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