Development of low background PMT R13111 2019/09/10 K. Abe - - PowerPoint PPT Presentation

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
• 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.
• 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

R10789 R13111

226Ra

• Large contributions are

from

• Glass beads
• Insulators for feedthrough
• 226Ra/228Ra/40K/238U
• Kovar metal parts for body

and stem

• 60Co
• Kovar metal has good

property to connect to quartz window, but it includes cobalt.

• Al sealing was another BG

source.

• 238U
• For reduction of RI,

concentrate effort to these parts.

• Exchange the parts to

cleaner ones.

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

40K

RI reduction: impurity R10789

60Co

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

238U

• 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 screening

RI of developed R13111

• RI for assembled PMT
• By measuring 13 PMTs in one

measurement, achieved high sensitivity.

• 226Ra ~0.4mBq/PMT
• 238U <1.6mBq/PMT
• 228Ra 0.3mBq/PMT
• 40K ~2mBq/PMT
• 60Co ~0.2mBq/PMT
• Two production lots at 2015 and at

2016 version uses same parts.

• Consistent results.
• We can control difference due to

different lot in this error level.

[mBq/PMT] 226Ra 238U 228Ra 40K 60Co R13111(2015)

0.38±0.07 <1.6 0.29±0.06 <1.4 0.22±0.05

R13111(2016)

0.44±0.06 <1.4 0.2±0.06 2.0±0.5 0.13±0.04 226Ra 238U 228Ra 40K 60Co mBq/PMT 0.5 1.0 2.5 R13111 2015

R13111 2016

1.5 2.0 3.0

• Large reduction from

R10789

• 226Ra ~1/3
• 228Ra ~1/3
• 40K

~1/5

• 60Co ~1/10
• Sensitive area difference

is not considered.

• R10789 2 inch
• R13111 3 inch
• Another factor of ~1/2

[mBq/PMT] 226Ra 238U 228Ra 40K 60Co R13111(2015)

0.38±0.07 <1.6 0.29±0.06 <1.4 0.22±0.05

R13111(2016)

0.44±0.06 <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 (XENON1T)

0.52±1.0 <13 0.39±0.1 12±0.2 0.74±0 .1

R13111 2015 R13111 2016 R10789 R11410

226Ra 238U 228Ra 40K 60Co mBq/PMT 5 10 15Comparison to Other PMTs

• Eur. Phys. J. C 75 (2015) 546 [arXiv:1503.07698[astro-ph.IM]]

RI in components of R13111：226Ra

• 0.10
• 0.05

0.00 0.05 0.10 0.15 0.20

石英ブロック 石英基板 スペーサーA,B ビス、ナット、ワッシャー KOVリング ハーメチック Milled HP Glass Getter ナンバー、スプリング Al-5N Dynode 2-11段目 ディスク止め Dy1-mesh アノードメッシュ カ… ステムピン ディスク シールド Dynode 1段目 蒸着用Al-5N Dy、PC用Sb リード線、リボン、ゲッター止め ステム チップ管 ステム 42Alloy側管 DY12段目

RI[mBq/PMT]

226Ra

• Contributions from each

components of the PMT.

• Basically error becomes small

for component whose amount used for one PMT is small. We can measure large amount at

• ne measurement.
• Contributions from glass

beads reduced largely.

• 1.6mBq/PMT(R10789)
• >0.016mBq/PMT
• Some stainless steel parts

have large contributions,

• Dynodes and shield.
• Stem’s contribution is not

significant, it has large error.

quartz support board spacer bis, nut, washer Kovar ring Hermetic glass beads Getter number, spring Al sealing Dynode2-11 Disk stopper Dy1 mesh, anode mesh stem pin Disc Shield Dy1 Al for evaporation Sb Lead line, ribbon Copper pipe Stem Body Dy12

RI in components of R13111

• 232Th, 40K, 60Co
• 3.00
• 2.00
• 1.00

0.00 1.00 2.00 3.00 4.00 5.00

石英ブロック 石英基板 スペーサーA,B ビス、ナット、ワッシャー KOVリング ハーメチック Milled HP Glass Getter ナンバー、スプリング Al-5N Dynode 2-11段目 ディスク止め Dy1-mesh アノードメッ… ステムピン ディスク シールド Dynode 1段目 蒸着用Al-5N Dy、PC用Sb リード線、リボン、ゲッ… ステム チップ管 ステム 42Alloy側管 DY12段目

RI[mBq/PMT]

238U

• 0.06
• 0.04
• 0.02

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14

石英ブロック 石英基板 スペーサーA,B ビス、ナット、ワッシャー KOVリング ハーメチック Milled HP Glass Getter ナンバー、スプリング Al-5N Dynode 2-11段目 ディスク止め Dy1-mesh アノードメッ… ステムピン ディスク シールド Dynode 1段目 蒸着用Al-5N Dy、PC用Sb リード線、リボン、ゲッ… ステム チップ管 ステム 42Alloy側管 DY12段目

RI[mBq/PMT]

228Ra

quartz support board spacer bis, nut, washer Kovar ring Hermetic glass beads Getter number, spring Al sealing Dynode2-11 Disk stopper Dy1 mesh, anode mesh stem pin Disc Shield Dy1 Al for evaporation Sb Lead line, ribbon Copper pipe Stem Body Dy12

quartz support board spacer bis, nut, washer Kovar ring Hermetic glass beads Getter number, spring Al sealing Dynode2-11 Disk stopper Dy1 mesh, anode mesh stem pin Disc Shield Dy1 Al for evaporation Sb Lead line, ribbon Copper pipe Stem Body Dy12

• Contributions from glass beads and Al sealing became negligible.
• 238U and 228Ra, no significant contributions were identified.

• 40K
• Glass beads contribution reduced from ~3mBq/PMT(R10789)->0.6mBq/PMT.
• Though still significant and major contribution.
• 60Co
• Body and stem changed from Kovar metal to Co free metal.
• Largest contribution comes from stem pin made from Kovar.
• 0.04
• 0.02

0.00 0.02 0.04 0.06 0.08 0.10

石英ブロック 石英基板 スペーサーA,B ビス、ナット、ワッシャー KOVリング ハーメチック Milled HP Glass Getter ナンバー、スプリング Al-5N Dynode 2-11段目 ディスク止め Dy1-mesh アノードメッ… ステムピン ディスク シールド Dynode 1段目 蒸着用Al-5N Dy、PC用Sb リード線、リボン、ゲッ… ステム チップ管 ステム 42Alloy側管 DY12段目

RI[mBq/PMT]

60Co

• 0.60
• 0.40
• 0.20

0.00 0.20 0.40 0.60 0.80 1.00

石英ブロック 石英基板 スペーサーA,B ビス、ナット、ワッシャー KOVリング ハーメチック Milled HP Glass Getter ナンバー、スプリング Al-5N Dynode 2-11段目 ディスク止め Dy1-mesh アノードメッ… ステムピン ディスク シールド Dynode 1段目 蒸着用Al-5N Dy、PC用Sb リード線、リボン、ゲッ… ステム チップ管 ステム 42Alloy側管 DY12段目

RI[mBq/PMT]

40K

RI in components of R13111

quartz support board spacer bis, nut, washer Kovar ring Hermetic glass beads Getter number, spring Al sealing Dynode2-11 Disk stopper Dy1 mesh, anode mesh stem pin Disc Shield Dy1 Al for evaporation Sb Lead line, ribbon Copper pipe Stem Body Dy12 quartz support board spacer bis, nut, washer Kovar ring Hermetic glass beads Getter number, spring Al sealing Dynode2-11 Disk stopper Dy1 mesh, anode mesh stem pin Disc Shield Dy1 Al for evaporation Sb Lead line, ribbon Copper pipe Stem Body Dy12

glass beads stem pin

[mBq/PMT] 226Ra 238U 228Ra 40K 60Co R13111(2015)

0.38±0.07 <1.6 0.29±0.06 <1.4 0.22±0.05

R13111(2016)

0.44±0.06 <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 (XENON1T)

0.52±1.0 <13 0.39±0.1 12±0.2 0.74±0 .1

R13111 2015 R13111 2016 R10789 R11410

226Ra 238U 228Ra 40K 60Co mBq/PMT 5 10 15RI reduction

• Eur. Phys. J. C 75 (2015) 546 [arXiv:1503.07698[astro-ph.IM]]
• Achieved Large

reduction

• Dirty parts

exchange worked quite well.

Problem of Xe leak

cfJINST 12 P01024 (2017) XENON1T PMT paper

• Xe leaks in R11410 have been reported by XENON1T and PandaX group during

the test inside liquid Xe.

• Afterpulse of Xe was observed.
• Similar leaks were found in R13111, it was not observed for R10789 in XMASS-I.

Study of Xe leak, R13111

• Applied many cooling cycles to

R13111 PMTs inside Xe.

• Very similar Xe leaks were observed

for R13111 in cooling test inside Xe.

• Check afterpulse rates for each gas

during cycles.

• Leaks are made at 1st or 2nd cooling.
• For many cases Xe leak increased with

every cooling cycle.

• Another cycle makes situation worse.
• Not all leaked PMT, for some cases rate

were not increased.

Xe++ Xe+ Ar CH4 He H afterpulse rate

time delay(nsec) pulse charge(pe)

• 100

deg room temp room temp

• 100

deg

• 100

deg room temp

Xe leaked PMT

Study of Xe leak

• Study to identify the cause and solve

the problem is ongoing.

• R11410 and R13111 have many

common structure as low BG Hamamatsu PMT.

• We are thinking the cause of the leaks is

same for both PMTs.

• No leaks were observed in R10789 used

in XMASS-I.

• Modification from R10789 can be the cause.
• Study is not yet finished.
• Another test is to start within a week
• Detail of the study will be written in

preparing paper which includes RI reduction.

afterpulse rate

• 100

deg room temp room temp

• 100

deg

• 100

deg room temp

Xe leaked PMT PMT without leak

Summary

• Developed new low BG PMT R13111 based on R10789
• 3 inch dome shaped photo-cathode.
• Large RI reduction.
• With increased sensitivity of measurement for screening.
• By exchanging parts which have large RI in R10789
• Glass beads.
• Kovar metal.
• Al sealing.
• …
• Xe leak problems.
• Troubles for R13111 and R11410.
• Study to identify the cause and solve the problem is ongoing.
• Details will be written in preparing paper.

Cooling test inside Xe.

• Test chamber to which Xe can be introduced.
• Top 7 PMTs, bottom 7 PMTs can be installed.
• 3 LEDs generate light in each blocked region.

PMT 3 LEDs ch8 ch9 ch10 ch11 ch12 ch13 ch14 ch4 ch3 ch2 ch1 ch6 ch5 ch7 LED PTFE wall thermometer top thermometer bottom

BG level of Kamioka Ge detector.

• https://indico.cern.ch/event/716552/s

essions/310927/attachments/1847769 /3032268/ScovellLRT_GeReview.pdf

• GeOroel, Asterix: Canfranc
• Belmont, Merrybent: Boulby
• GePaolo, GeCris, GeMPI: LNGS
• LabC: Kamioka lowest BG, factor ~3

better (contiuous component) than

• thers in Kamioka.
• Very low BG level compared to other

facilities.

Integral Integral

Components of R13111

• Total 25 parts.

Ge specially prepared for low RI measurement.

• 80% p-type for low RI measurement
• Shield prepared by ourselves.
• 6N copper 1cm
• Copper 5cm
• Low 210Pb lead (~5Bq/kg) 2.5cm
• Lead (~140Bq/kg) 20cm
• Large sample chamber ~10L
• Suited for large sample, such as assembled PMT.

Introduction

• In low background experiment. Largest

background are

• Ri in detector components
• Surface structure origined BG.
• For XMASS, some surface events are wrongly

reconstructed as fiducial volume.

• PMT, most important component
• 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
• Low background
• Dome shape to identify surface BG clearly.
• Developed based on R10789

XMASS-I, estimated background events inside fiducial volume after all selection. PMT PMT Surface BG budget in XMASS-I

Problem of Xe leak

time from first pulse pe KA0057 Ｈ CH4 Ｈe Ar Kobayashi-san calculated

• Measured sensitivity of PMT side part,

normalized by sensitivity at dome top by using 10~15PE level laser light.

• High sensitivity >80% for whole side part

is achieved.