1. 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 EachTotal R7525 HA$246.41665 k$ R7525 HA-μ$265.55717 k$ R7525 CC-HA$360.29973 k$ R7525 CC-HA-μ$ 377.641020 k$

2. 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 (E>100 keV 1.6x1012, E>20 MeV 5.1x1011) –Expect transmission loss of a few percent over ten years; – not a problem.

3. Is Boron in Window a problem? B 10 5 + n 1 0 -> Li 7 3 +  4 2 +2.792 MeV (gnd state) 6% B 10 5 + n 1 0 -> *Li 7 3 +  4 2 +2.310 MeV (ex state) 94% E  = 1.47 MeVE Li = 0.84 MeV The natural abundance of B 10 5 is 19.8 % Alpha particle ranges out in ~450  m *Li gives out 0.43 MeV gamma with  ~ 10 -13 sec For thermal neutrons (< 0.025 eV),  ~ 3840 b At PMT location,  n ~ 10 kHz/cm 2 d  /dt =  n A  D N  ~ 1000  /sec, E  = 1.47 MeV T max ~ 2 m e c 2  2  2 ~ 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/  =18 –Electrons with E<100 eV /  =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.

4. 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/cm 2. 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. –2x10 10 ch/cm 2 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.

5. Other Issues Scintillation of the PMT window is only a concern if the dose rate is >0.03 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).

6. Hammamatsu ItemSpecificationsR7525 Anode current vs. cathode position +- 20%, 3mm spot+- 30%, 3mm spot Gain10 5 at 75% V KA (max10 5 at 80% V KA Single pe resolution50% or better65% or better Stability+-3% within any 48 hourOK after 10 hr. warmup EnvelopeOpaque and conductiveGraphite +PVC WindowPlaner or convexConvex cost + 50% Samples are on hand

7. Photonis ItemSpecificationXP2960XP3182 Pc diameter22-28 mm23 mm21 mm Gain10 4 -10 5 2x10 4 -2x10 6 10 5 -10 6 Transit time<25ns preferred 19 ns33 ns Pe resolution50% or better70% Convex-concave window is not available. Samples are being sent.

8. 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

9. 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. 3600 C (~40%) 360 C (~10%) 180 C SAFE I ave = 0.1 mA

10. Lifetime - II 260 C (~15 %) 26 C These estimates are based on 0.25 pe/GeV and gain of 4x10 4 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.

11. Magnetic Field The external magnetic field around the ROBox region is small (<0.0023 T). Therefore it is not difficult to magnetically shield the PMTs to satisfactory levels. Shielding factor = 3  t/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.