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Reactor On/Off Monitoring with a Prototype of Plastic Anti-neutrino Detector Array (PANDA). Yasuhiro Kuroda A , Yo Kato A , Nozomu Tomita A , Ryoko Nakata, Shugo Oguri , Chikara Ito B , Yoshizumi Inoue C , Makoto Minowa A,D - PowerPoint PPT Presentation
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Reactor On/Off Monitoring with a Prototype of Plastic Anti-neutrino Detector Array (PANDA)
Yasuhiro KurodaA, Yo KatoA, Nozomu TomitaA, Ryoko Nakata, Shugo Oguri, Chikara ItoB, Yoshizumi InoueC, Makoto MinowaA,D
Department of Physics, School of Science University of TokyoA
Japan Atomic Energy AgencyB
International Center of Elementary Particle Physics, University of TokyoC
RSCEU, University of TokyoD
AAP2012 - the University of Hawaii, Manoa Campus2
Neutrino Reactor Monitoring
• IAEA reactor safeguard regime– IAEA recommends investigation of near-field antineutrino monitoring
capabilities• IAEA : Medium term goal
Cf ) IAEA Headquarters, Final Report: Focused Workshop on Antineutrino Detection for Safeguards Applications (2008)
– Above ground deployment– Provide fully independent measurements of fissile content, through
the use of spectral information– Reduced detector footprint
• Our Efforts– Mobile above-ground detector– Segmented detector
October 4, 2012
AAP2012 - the University of Hawaii, Manoa Campus3
PANDA
Plastic Anti-Neutrino Detector Array
October 4, 2012
• The proposed final detector consists of 10x10 modules
• The target mass : about 1 ton
• PANDA detector is designed to be loaded and operated on a van.
AAP2012 - the University of Hawaii, Manoa Campus4
PANDA Module
• 10cm × 10cm × 100cm plastic scintillator– Easy to transport– Non flammable
• Wrapped in gadolinium doped sheets (Gd:4.9mg/cm2)
– Technique to create clear and colorless Gd doped plastic scintillator is less established
October 4, 2012
PMT light guideAluminised Mylar
Gd sheet
Plastic scintillator
AAP2012 - the University of Hawaii, Manoa Campus5
Detection Principle
• Inverse beta decayνe + p → e+ + n
• Prompt event– Energy deposit of e+
– e++e-→2γ• Delayed Event
– An 8 MeV gamma-ray cascade following neutron capture on the gadolinium
• Delayed coincidence method
October 4, 2012
AAP2012 - the University of Hawaii, Manoa Campus6
First Prototype: Lesser PANDA
• 16 modules (4x4)
October 4, 2012
• Background measurement at Hamaoka Nuclear Power Plant Unit3Nucl.Instrum.Meth.A690:41-47,2012
2010 → 2011
AAP2012 - the University of Hawaii, Manoa Campus7
Second Prototype : PANDA36
• 36 modules (6x6)
October 4, 2012
2011 → 2012
• Our first reactor on/off measurement by neutrino is done by PANDA36
AAP2012 - the University of Hawaii, Manoa Campus8
Data Acquisition
• 72ch PMT charge data• Event timing information (time stamp)
October 4, 2012
72 × PMT
5×16ch discriminator
3×32ch charge ADC
72×PMT output data
85%
15%
AAP2012 - the University of Hawaii, Manoa Campus9
Remote Monitoring for unmanned operation
October 4, 2012
DAQ DAQ controlServer
Thermo-hygrometerConnected to
LAN
MonitoringServer
RouterDoCoMo terminal
with Global IP
data storage(HDD)
Nuclear Power Plant
Simplified spectrum
Temperature / humidity monitoring
Alert mails
-Simple DAQ control (for emergency)- Network connection confirmation
- Digest- Alert Mails
- Web server- Sending alert mails- Network connection confirmation
• Possible defects are checked through DoCoMo cellular phone network and the Internet
Hongo CampusUniv.Tokyo
WebCamera
AAP2012 - the University of Hawaii, Manoa Campus10
Typical cosmic muon event
October 4, 2012
Energy deposit PositionStage 6
Stage 5
Stage 4
Stage 3
Stage 2
Stage 1
Stage 6
Stage 5
Stage 4
Stage 3
Stage 2
Stage 1
Position (cm)-60 600
Position (cm)-60 600
AAP2012 - the University of Hawaii, Manoa Campus11
Loading on a van
• PANDA36 was loaded on a 2-ton van
October 4, 2012
AAP2012 - the University of Hawaii, Manoa Campus12
Ohi Power Station
October 4, 2012
Ohi Power Station
Mihama Power Station
Fukui
• PANDA36 was moved to Ohi Power Station
AAP2012 - the University of Hawaii, Manoa Campus13
Ohi Power Station : Unit2
October 4, 2012
Start EndReactor on Nov. 18, 2011 Dec. 16, 2011
Reactor off (background) Dec. 16, 2011 Jan. 18, 2012
3.4GWth
35.9 m
PANDA36
AAP2012 - the University of Hawaii, Manoa Campus14
Backgrounds
• Accidental Backgrounds– Natural radioactivity (gammas)– Thermal neutrons
• Correlated Backgrounds– Fast neutrons (proton recoil)
extremely important – Double neutron capture– Long-lived cosmic-ray activation product
We tried to reject these backgrounds by event selections.
October 4, 2012
AAP2012 - the University of Hawaii, Manoa Campus15
Event Selection - 1 (neutrino)
October 4, 2012
E1st E2nd Etotal
prompt event
3MeV E≦ total 6MeV≦E2nd 520keV (annihilation gamma)≦E1st module must be in inside 16 modules
(fiducial cut)
delayed event
3MeV E≦ total 8MeV≦
E3rd/Etotal (E≦ 1st/Etotal-0.5)/5
Time window: 8-150μsec
Two or more modules in inside 16 modules deposite the energy of 150keV (software trigger)≧
There is no event with Etotal > 8MeV within250μs before the delayed event (muon veto)
AAP2012 - the University of Hawaii, Manoa Campus16
Event Selection - 1 (neutrino)
October 4, 2012
prompt event
3MeV E≦ total 6MeV≦E2nd 520keV (annihilation gamma)≦E1st module must be in inside 16 modules
(fiducial cut)
delayed event
3MeV E≦ total 8MeV≦
E3rd/Etotal (E≦ 1st/Etotal-0.5)/5
Time window: 8-150μsec
Two or more modules in inside 16 modules deposite the energy of 150keV (software trigger)≧
There is no event with Etotal > 8MeV within250μs before the delayed event (muon veto)
AAP2012 - the University of Hawaii, Manoa Campus17
Event Selection - 1 (neutrino)
October 4, 2012
prompt event
3MeV E≦ total 6MeV≦E2nd 520keV (annihilation gamma)≦E1st module must be in inside 16 modules
(fiducial cut)
delayed event
3MeV E≦ total 8MeV≦
E3rd/Etotal (E≦ 1st/Etotal-0.5)/5
Time window: 8-150μsec
Two or more modules in inside 16 modules deposite the energy of 150keV (software trigger)≧
There is no event with Etotal > 8MeV within250μs before the delayed event (muon veto)
AAP2012 - the University of Hawaii, Manoa Campus18
Event Selection - 1 (neutrino)
October 4, 2012
prompt event
3MeV E≦ total 6MeV≦E2nd 520keV (annihilation gamma)≦E1st module must be in inside 16 modules
(fiducial cut)
delayed event
3MeV E≦ total 8MeV≦
E3rd/Etotal (E≦ 1st/Etotal-0.5)/5
Time window: 8-150μsec
Two or more modules in inside 16 modules deposite the energy of 150keV (software trigger)≧
There is no event with Etotal > 8MeV within250μs before the delayed event (muon veto)
Observed event rate difference: 38.4 ± 8.4 events/day (large?)
Preliminary
Detection efficiency: (3.15±0.93)%Predicted anti-neutrino rate:
18.1±6.5 events/day
AAP2012 - the University of Hawaii, Manoa Campus19
Event Selection - 2 (neutron)
• Selection intended to select fast neutron events
• E2nd condition is changed to reject the anti-neutrino events
October 4, 2012
prompt event
3MeV E≦ total 6MeV≦E2nd 700keV≧
E1st module must be in inside 16 modules (fiducial cut)
delayed event
3MeV E≦ total 8MeV≦
E2nd/Etotal (E≦ 1st/Etotal-0.5)/5
Time window: 8-50μsec
Two or more modules in inside 16 modules deposite the energy of 150keV (software trigger)≧
There is no event with Etotal > 8MeV within250μs before the delayed event (muon veto)
AAP2012 - the University of Hawaii, Manoa Campus20
Event Selection - 2 (neutron)
Neutrino detection efficiency: (0.271±0.93) % ~ 0%
Observed event rate change: 31.4 ± 8.5 events/day
October 4, 2012
Preliminary
prompt event
3MeV E≦ total 6MeV≦E2nd 700keV≧
E1st module must be in inside 16 modules (fiducial cut)
delayed event
3MeV E≦ total 8MeV≦
E3rd/Etotal (E≦ 1st/Etotal-0.5)/5
Time window: 8-50μsec
Two or more modules in inside 16 modules deposite the energy of 150keV (software trigger)≧
There is no event with Etotal > 8MeV within250μs before the delayed event (muon veto)
AAP2012 - the University of Hawaii, Manoa Campus21
Reactorbuilding
PANDA
2.5m
2.8m
Water tank
Change of the fast neutron flux
• Why did the fast neutron flux change?– It’s not so clear…
But we speculated that it could be explained by changes in environment.
– Three water tanks (used for scheduled inspection of the reactor)
– Water could shield the fast neutrons
October 4, 2012
AAP2012 - the University of Hawaii, Manoa Campus22
Preliminary
Change of the neutrino flux
Simultaneous equation to evaluate the change of the neutrino event rate
October 4, 2012
(selection-1)
(selection-2)
: the contribution of the neutrino rate by selection-1: the contribution of the fast-neutron rate difference by selection-1
: the ratio of the neutrino and neutron detection efficiencies (0.086±0.026 and 1.86±0.68 respectively).
events/day7.119.22 x (expected : 18.1±6.5 events/day )
≈0
AAP2012 - the University of Hawaii, Manoa Campus23
Next Step
• Unexpectedly large change in fast-neutron flux
• It could be subtracted using the second selection. But the subtraction increases the error.→ Water Shielding? (at the expense of small size and light weight)
• 8x8=64 prototype– Designing new structure which
includes shieldings– Estimating expected performance of
next prototype
October 4, 2012
AAP2012 - the University of Hawaii, Manoa Campus24
Summary
• 6x6 prototype of PANDA (PANDA36) was built• It was loaded on a van and deployed above
ground at Ohi Power Station Unit 2 (3.4GWth)• Fully unmanned operation was demonstrated• Detected neutrino event rate was
22.9±11.7 events/day (expected: 18.5±6.5 events/day)
• Next upgrade to 8x8 is on going. It may have neutron shielding
October 4, 2012
Backups
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Gadolinium doped sheet
• Gd density : 4.9mg/cm2
• 60% Of thermal neutrons are captured by one layer of the sheet (84% by two layer)
October 4, 2012
50μm
PET sheet Gd doped ink layer
AAP2012 - the University of Hawaii, Manoa Campus27
VME Modules
Module Model
Discriminator CAEN V89516 Channel Leading Edge Discriminator
FPGA module CAEN V1495General Purpose VME Board (It has user customizable FPGA Unit)
Multi-event charge ADC CAEN V79232 Channel Multi-event QDC
October 4, 2012
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Cosmogenic Radioisotopes
• 9Li, 8He– Decay time constant :
• 9Li : 178 ms • 8He : 119ms
• β-decay isotopes with a delayed neutron emission from the β decayed daughter
• This background is negligible with a small detector. And it is strongly rejected by prompt event selection criteria
E2nd 520keV ≦taking advantage of segmented design.
October 4, 2012
AAP2012 - the University of Hawaii, Manoa Campus29
Double neutron capture
• Double neutron capture– It is strongly rejected by
prompt event selection criteria
E2nd 520keV ≦taking advantage of segmented design
October 4, 2012
Spectra of E2nd of the prompt events after selection-1 (neutrino selection) except for the prompt E2nd selection.
AAP2012 - the University of Hawaii, Manoa Campus30
Selection : prompt - Etotal
October 4, 2012
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Selection : prompt – fiducial cut
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Selection : delayed - Etotal
October 4, 2012
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Accidental Events
• Observed accidental background rates using other time windows– Selection-1 : 8μs+1ms t 150μs+1ms≦ ≦– Selection-2 : 8μs+1ms t 50μs+1ms≦ ≦
October 4, 2012
Selection - 1 Selection - 2
Preliminary Preliminary