Development of low background PMT R13111 2019/09/10 K. Abe
Contents • Introduction • Development of R13111 based on R10789 • RI reduction • Ge detectors for screening • RI for R113111 • Assembled R13111 • Comparison to other PMTs. • RIs from each components. • Xe leak problem of low BG PMT.
Introduction • Major background source in low background experiment • RI in detector components • Surface structure originated BG. • Distorted events by the surface structure sometimes mimic signals. • For XMASS, some surface events are wrongly reconstructed as fiducial volume. • PMT, one of the most important component • Used in many experiments. • In many cases, contains largest RI. • Large volume and material amount. • Some parts are difficult to change to keep performance. • New low background PMT, R13111 • For LXe detector • Low RI • Dome shape to identify surface BG clearly.
Development of PMT R13111 • 3 inch convex photo-cathode R10789 • For effective surface event identification. • For liquid Xe detector • Large RI reduction was done. • Developed based on on R10789 • R10789 • Low RI PMT developed for XMASS-I. R13111 • Hex shape photo-cathode to cover the area effectively. • ~mBq/PMT amount of radioactivity for each RI • Still one of the largest BG source in XMASS-I. 4
RI reduction: impurity R10789 • Large contributions are 40K 226Ra from • Glass beads • Insulators for feedthrough • 226Ra/228Ra/40K/238U • Kovar metal parts for body and stem dynodes electrodes Body, Hex Body, Cylinder Stem Glass beads Lead line Quartz Al sealing Getter dynodes electrodes Body, Hex Body, Cylinder Stem Glass beads Lead line Quartz Al sealing Getter • 60Co • Kovar metal has good property to connect to quartz window, but it includes cobalt. 60Co 238U • Al sealing was another BG source. • 238U • For reduction of RI, concentrate effort to these parts. • Exchange the parts to dynodes electrodes Body, Hex Body, Cylinder Stem Glass beads Lead line Quartz Al sealing dynodes electrodes Body, Hex Body, Cylinder Stem Glass beads Lead line Quartz Al sealing Getter cleaner ones.
RI screening • RI reduction by screening with RI measurement. • Ge and mass spectrometer • Ge detectors used for this screening. • 3 p-type detectors • 100%, relative efficiency • 120%, diameter 83mm, height 86mm • 80% • specially prepared for low RI measurement. • Large sample chamber to measure large sample and large amount, such as assembled PMT. • n-type • 110%, diameter 80.5mm height 80.5mm • Sensitivity increase from R10789 development • Increase amount of samples in one measurement. • New low BG Ge. • 0.1 mBq/PMT -> 0.01 mBq/PMT
RI of developed R13111 • RI for assembled PMT • By measuring 13 PMTs in one measurement, achieved high 3.0 sensitivity. mBq/PMT 2.5 R13111 2015 • 226Ra ~0.4mBq/PMT R13111 2016 • 238U <1.6mBq/PMT 2.0 • 228Ra 0.3mBq/PMT • 40K ~2mBq/PMT 1.5 • 60Co ~0.2mBq/PMT 1.0 • Two production lots at 2015 and at 2016 version uses same parts. 0.5 • Consistent results. 0 • We can control difference due to 226Ra 238U 228Ra 60Co 40K different lot in this error level. [mBq/PMT] 226Ra 238U 228Ra 40K 60Co 0.38 ± 0.07 <1.6 0.29 ± 0.06 <1.4 0.22 ± 0.05 R13111(2015) 0.44 ± 0.06 <1.4 0.2 ± 0.06 2.0 ± 0.5 0.13 ± 0.04 R13111(2016)
15 Comparison to Other PMTs • Large reduction from R10789 mBq/PMT • 226Ra ~1/3 R13111 2015 • 228Ra ~1/3 R13111 2016 • 40K ~1/5 10 R10789 • 60Co ~1/10 R11410 • Sensitive area difference is not considered. 5 • R10789 2 inch • R13111 3 inch • Another factor of ~1/2 0 228Ra 40K 60Co 238U 226Ra [mBq/PMT] 226Ra 238U 228Ra 40K 60Co 0.38 ± 0.07 <1.6 <1.4 R13111(2015) 0.29 ± 0.06 0.22 ± 0.05 0.44 ± 0.06 R13111(2016) <1.4 0.2 ± 0.06 2.0 ± 0.5 0.13 ± 0.04 R10798 1.2 ± 0.3 1.9 (Parts sum) <0.78 9.1 ± 2.2 2.8 ± 0.2 R11410-21 0.52 ± 1.0 <13 0.39 ± 0.1 12 ± 0.2 0.74 ± 0 .1 (XENON1T) Eur. Phys. J. C 75 (2015) 546 [arXiv:1503.07698[astro-ph.IM]]
RI[mBq/PMT] -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 RI in components of R13111 ： 226Ra quartz 石英ブロック 226Ra support board 石英基板 spacer スペーサー A,B bis, nut, washer ビス、ナット、ワッシャー Kovar ring KOV リング Hermetic ハーメチック glass beads Milled HP Glass Getter Getter number, spring ナンバー、スプリング Al sealing Al-5N Dynode2-11 Dynode 2-11 段目 Disk stopper ディスク止め Dy1 mesh, anode mesh Dy1-mesh アノードメッシュ カ… stem pin ステムピン Disc ディスク Shield シールド Dy1 Dynode 1 段目 Al for evaporation 蒸着用 Al-5N Sb Dy 、 PC 用 Sb Lead line, ribbon リード線、リボン、ゲッター止め Copper pipe ステム チップ管 Stem ステム Body 42Alloy 側管 DY12 段目 Dy12 • Some stainless steel parts • Contributions from glass • Basically error becomes small • Contributions from each have large contributions, beads reduced largely. one measurement. can measure large amount at used for one PMT is small. We for component whose amount components of the PMT. • Stem’s contribution is not • Dynodes and shield. • 1.6mBq/PMT(R10789) significant, it has large error. ->0.016mBq/PMT
RI[mBq/PMT] • 238U and 228Ra, no significant contributions were identified. • Contributions from glass beads and Al sealing became negligible. -3.00 -2.00 -1.00 0.00 1.00 2.00 3.00 4.00 5.00 • 232Th, 40K, 60Co RI in components of R13111 quartz 石英ブロック support board 238U 石英基板 spacer スペーサー A,B bis, nut, washer ビス、ナット、ワッシャー Kovar ring KOV リング Hermetic ハーメチック glass beads Milled HP Glass Getter Getter number, spring ナンバー、スプリング Al sealing Al-5N Dynode2-11 Dynode 2-11 段目 Disk stopper ディスク止め Dy1 mesh, anode mesh Dy1-mesh アノードメッ… stem pin ステムピン Disc ディスク Shield シールド Dy1 Dynode 1 段目 Al for evaporation 蒸着用 Al-5N Sb Dy 、 PC 用 Sb Lead line, ribbon リード線、リボン、ゲッ… Copper pipe ステム チップ管 Stem ステム Body 42Alloy 側管 Dy12 DY12 段目 RI[mBq/PMT] -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 quartz 石英ブロック support board 石英基板 228Ra spacer スペーサー A,B bis, nut, washer ビス、ナット、ワッシャー Kovar ring KOV リング Hermetic ハーメチック glass beads Milled HP Glass Getter Getter number, spring ナンバー、スプリング Al sealing Al-5N Dynode2-11 Dynode 2-11 段目 Disk stopper ディスク止め Dy1 mesh, anode mesh Dy1-mesh アノードメッ… stem pin ステムピン Disc ディスク Shield シールド Dy1 Dynode 1 段目 Al for evaporation 蒸着用 Al-5N Sb Dy 、 PC 用 Sb Lead line, ribbon リード線、リボン、ゲッ… Copper pipe ステム チップ管 Stem ステム Body 42Alloy 側管 Dy12 DY12 段目
RI[mBq/PMT] -0.60 -0.40 -0.20 0.00 0.20 0.40 0.60 0.80 1.00 • 60Co • 40K RI in components of R13111 quartz • Largest contribution comes from stem pin made from Kovar. • Body and stem changed from Kovar metal to Co free metal. • Though still significant and major contribution. • Glass beads contribution reduced from ~3mBq/PMT(R10789)->0.6mBq/PMT. 石英ブロック support board 40K 石英基板 spacer スペーサー A,B bis, nut, washer ビス、ナット、ワッシャー Kovar ring KOV リング Hermetic ハーメチック glass beads Milled HP Glass Getter beads glass Getter number, spring ナンバー、スプリング Al sealing Al-5N Dynode2-11 Dynode 2-11 段目 Disk stopper ディスク止め Dy1 mesh, anode mesh Dy1-mesh アノードメッ… stem pin ステムピン Disc ディスク Shield シールド Dy1 Dynode 1 段目 Al for evaporation 蒸着用 Al-5N Sb Dy 、 PC 用 Sb Lead line, ribbon リード線、リボン、ゲッ… Copper pipe ステム チップ管 Stem ステム Body 42Alloy 側管 Dy12 DY12 段目 RI[mBq/PMT] -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 quartz 石英ブロック support board 石英基板 60Co spacer スペーサー A,B bis, nut, washer ビス、ナット、ワッシャー Kovar ring KOV リング Hermetic ハーメチック glass beads Milled HP Glass Getter Getter number, spring ナンバー、スプリング Al sealing Al-5N Dynode2-11 Dynode 2-11 段目 Disk stopper ディスク止め Dy1 mesh, anode mesh Dy1-mesh アノードメッ… stem pin ステムピン Disc ディスク Shield シールド pin stem Dy1 Dynode 1 段目 Al for evaporation 蒸着用 Al-5N Sb Dy 、 PC 用 Sb Lead line, ribbon リード線、リボン、ゲッ… Copper pipe ステム チップ管 Stem ステム Body 42Alloy 側管 Dy12 DY12 段目
15 RI reduction • Achieved Large reduction mBq/PMT R13111 2015 • Dirty parts R13111 2016 exchange worked 10 R10789 quite well. R11410 5 0 228Ra 40K 60Co 238U 226Ra [mBq/PMT] 226Ra 238U 228Ra 40K 60Co 0.38 ± 0.07 <1.6 <1.4 R13111(2015) 0.29 ± 0.06 0.22 ± 0.05 0.44 ± 0.06 R13111(2016) <1.4 0.2 ± 0.06 2.0 ± 0.5 0.13 ± 0.04 R10798 1.2 ± 0.3 1.9 (Parts sum) <0.78 9.1 ± 2.2 2.8 ± 0.2 R11410-21 0.52 ± 1.0 <13 0.39 ± 0.1 12 ± 0.2 0.74 ± 0 .1 (XENON1T) Eur. Phys. J. C 75 (2015) 546 [arXiv:1503.07698[astro-ph.IM]]
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