Hamamatsu R7525

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Hamamatsu R7525

• HA outer conductive coating with insulating
  sleeve
• CC convex-concave window 0.5-0.6 mm thick
  (standard plano-concave 1mm center, 6.1 mm edge)
• µ soft mu-metal shield wrap
• 2700 units
• 3 month lead time ARO
• 200 units/month delivery rate

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Neutrons on Glass

• PMT window materials (silica and borosilicate)
  were studied in a reactor and compared with other
  data
• 6 x 1012 n/cm2
• 4.1 x 1013 n/cm2(Hamamatsu points at 14 MeV, red)
• 2.5 x 1014 n/cm2(Hamamatsu points at 14 MeV,
  blue)
• 6 x 1014 n/cm2
• Expected total neutron fluence at the PMTs is 2.5
  x 1012 n/cm2 in 10 years (Egt100 keV 1.6x1012,
  Egt20 MeV 5.1x1011)
• Expect transmission loss of a few percent over
  ten years
• not a problem.

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Is Boron in Window a problem?

• B105 n10 -gt Li73a422.792 MeV (gnd state) 6
• B105 n10 -gt Li73a422.310 MeV (ex state) 94
• Ea 1.47 MeV ELi 0.84 MeV
• The natural abundance of B105 is 19.8
• Alpha particle ranges out in 450 mm
• Li gives out 0.43 MeV gamma with t 10-13 sec
• For thermal neutrons (lt 0.025 eV), s 3840 b
• At PMT location, Fn 10 kHz/cm2
• da/dt Fn A r D N s 1000 a/sec, Ea 1.47 MeV
• Tmax 2 mec2b2g2 0.8 keV
• R 0.7 T 1.7 88 nm
• Cook all of these numbers with simulation and get
• Alphas produced in glass 1000 /sec
• Alphas entering photocathode 226 /sec
• Electrons entering PMT/a 18
• Electrons with Elt100 eV /a 12
• Conclusion is that there will be 0.02 alphas per
  event per HF side with a mean energy of 12 GeV.
  This is not a problem and verified with MC.

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Radiation Backgrounds around PMTs

• This problem has been recently revisited and the
  present shielding system looks OK (20 cm steel,
  18 cm polyethylene, 2 cm aluminum). The holes
  (2.5 cm dia.) for the light guides are included
  in the these calculations. The charged hadrons
  and neutrons are 100 Hz/cm2. The photon rate is
  higher at 10000 and we are trying to do something
  about that.
• The PMT window is a potential source for
  Cherenkov radiation from charged particles.
• 2x1010 ch/cm2 for 10 years give 10-5 PMTs/xing.
  If 20 pe/PMT (1-3 mm thick window), 2x10-4
  pe/(xing PMT)
• If an isolated particle hits a PMT window, it
  would represent 80 GeV.

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Other Issues

• Scintillation of the PMT window is only a concern
  if the dose rate is gt0.03 rad/sec. For HF, the
  estimate is 0.00002 rad/sec (factor of 1000
  less).
• Ambient He partial pressure in air (0.53 Pa) will
  not be a problem with borosilicate window.
  Partial pressure will change 10 times in 10 years
  but will remain below the danger level by a
  factor of 50000.
• Nitrogen gas will be circulated inside the ROBox
  against He leak from cryogenics and temperature
  fluctuations (/- 2 degrees should not be a
  problem).

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Hammamatsu
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Photonis
Convex-concave window is not available. Samples
are being sent.
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Electron Tube

• Two candidates, D843WSB and D844WSB, meet all
  preliminary specifications, with no exceptions
  noted. Final data sheets not yet in hand.
• Both tubes come with 1 mm convex-concave windows
  of uv-transmitting glass.
• 843 longer with better linearity range and lower
  after each pulse.
• 844 shorter with better rise time and transit
  time.
• Samples are being sent

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Lifetime - I

• Aging is suspected to be dependent on the
  total accumulated charge. Charge rate is not
  relevant at 10 micro amps average anode current.

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Lifetime - II

• These estimates are based on 0.25 pe/GeV and gain
  of 4x104 for ten calendar years.
• There does not seem to be a drastic problem with
  PMT aging based on what we know now.
• The gain loss is recoverable by voltage increase.

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Magnetic Field

• The external magnetic field around the ROBox
  region is small (lt0.0023 T). Therefore it is
  not difficult to magnetically shield the PMTs to
  satisfactory levels.
• Shielding factor 3mt/4r 3000 for the mu-shield
  and there is another factor of 4 from the soft
  iron tube around the PMTs which results in the
  effective suppression factor of 12000.

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