From: Steve Biller (Steven.Biller@physics.ox.ac.uk)
Date: Thu Jun 02 2005 - 05:33:24 CDT
Most blackening agents are trouble in terms of radioactivity.
My choice would be not to blacken the inside of the tanks at all,
but to instead secure each PMT in a hexagonal cell made of black
ABS plastic (similar to SNO), which has been verified to be relatively
low in radioactivity. In fact, Nick and I have a scheme for constructing
essentially "self-contained" hexgonal boxes which each hold 6 PMTs
and are secured to the vessel wall with a simple bolt. Each unit
could be fully tested etc. at a lab and then transported to site,
with pre-attached cables guided along the back of the boxes and
secured in pre-cut grooves during installation. These boxes would
allow us to trivially encorporate light cones, should we choose to
do so, and would solve another important problem by providing
a structure which is secure but flexible so as to cushion the PMTs
during moving operations.
- Steve
Hans Jostlein wrote:
>Thanks, Janet
>
>Do we know what the maximum allowed wall reflectivity is?
>We may be able to get black steel which would be just a thin oxide coating.
>
>Hans
>
>
>----- Original Message -----
>From: "Janet Conrad" <conrad@nevis.columbia.edu>
>To: "Josh R Klein" <jrk@mail.hep.utexas.edu>
>Cc: "Matthew Worcester" <mworcest@hep.uchicago.edu>; "Joseph Formaggio"
><josephf@u.washington.edu>; <braidwood@hep.uchicago.edu>; "Paul Nienaber"
><nienaber@fnal.gov>
>Sent: Wednesday, June 01, 2005 10:51 AM
>Subject: Re: pmt glass radiation
>
>
>
>>Hi,
>>
>>As long as we are testing materials: What paint are we using to blacken
>>the
>>inside of the tank?
>>
>>On MiniBooNE we chose the materials to assure that the oil would not be
>>poisoned.
>>Andrew Bazarko did a really impressive range of studies and
>>it was quite striking what happened to the oil with many kinds of paints
>>and epoxies.
>>
>>We must take care.
>>
>>Note that on MiniBooNE, where events are >50 MeV, we didn't worry about
>>contamination.
>>
>>We chose an epoxy to dip the tubes and a Sherwin-Williams paint for the
>>light-tight
>>panels. Joe, I may be able to get you some of the paint and the
>>epoxy and we
>>could test it. I'll contact Andrew.
>>
>>Also, we have a facility here called "MiniMiniBooNE" which we may be
>>able to use
>>to do some tests. It is painted with MiniBooNE paint and has a
>>distance of about 40 cm
>>tube face to edge of tank. We might be able to use this to test the
>>rate from the tubes and
>>also the background rate from the paint. It isn't clear to me that we
>>will be allowed
>>to fill this with scintillator oil (MiniBooNE does not used doped oil,
>>so we would have to
>>be able to clean it out very very well before the next MiniBooNE
>>tests). But I can check.
>>Paul Nienaber will send out some dimensions and info on the test setup
>>later...
>>
>>-Janet
>>
>>Josh R Klein wrote:
>>
>>
>>>Joe,
>>> Just to add to Janet's note: the electronics components in the SNO tube
>>>
>bases
>
>>>are probably a larger contribution than the glass in terms of
>>>
>radioactivity. We
>
>>>might look into getting un-painted SMD's for our bases if we were worried
>>>
>about
>
>>>this.
>>>
>>>Josh
>>>
>>>On Wed, Jun 01, 2005 at 10:24:42AM -0500, Janet Conrad wrote:
>>>
>>>
>>>
>>>>Hi Joe,
>>>>
>>>>If I gave you a tube, with base, dipped in the protective enamel, could
>>>>you send it to
>>>>your low backgorund counting facility and have them measure the rates
>>>>and what is coming out?
>>>>Because there is more than just the tube -- there is the basis, the
>>>>protective coating, etc.
>>>>It would be nice to know where we stand with the whole package.
>>>>
>>>>-Janet
>>>>
>>>>
>>>>Matthew Worcester wrote:
>>>>
>>>>
>>>>
>>>>
>>>>>Hi Joe,
>>>>>
>>>>>Thanks again for the talk. I think the background must scale much
>>>>>more like the amount of material. So if you assume equal density of
>>>>>the glass, we should scale by volume. Assuming the 5912 is a 5 mm
>>>>>thick sphere and that the 2" tube is also 5 mm thick I get about 6
>>>>>Bq/pmt for the 8" tube, which is ballpark.
>>>>>
>>>>>Cheers,
>>>>>Matt
>>>>>
>>>>>On Tue, 31 May 2005, Joseph Formaggio wrote:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>>Dear Matt,
>>>>>>
>>>>>> Forgive me if I have sent you this talk before. It is a talk from
>>>>>>Moriyama from LRT2004. If you check out his slide 14, he quotes
>>>>>>~0.025 decays/sec/PMT, though these are much smaller PMTs (2").
>>>>>>However, scaling to an 8" tube, that means a rate of ~0.4 Hz/tube
>>>>>>(rather than 10). However, the background may not scale simply with
>>>>>>area. Hamamatsu does not list the R8778 in their catalog, so it
>>>>>>might be what we would expect to see in the future.
>>>>>>
>>>>>>Hope it helps,
>>>>>>Joe
>>>>>>
>>>>>>
>>>>>>
>>>>
>>
>>
>
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