DEMONSTRATION OF ZICOS EXPERIMENT FOR
OBSERVATION OF ZIRCONIUM-96 TWO NEUTRINO
EMISSION DOUBLE BETA DECAYXVIII International Conference on Topics in Astroparticle andUnderground Physics 2023 (TAUP2023)

August 29, 2023
University of Vienna
Grant-in-Aid for Scientific Research on Innovative Areas
19H05093 and 20H05241
Scientific Research (B) 22H01243
Miyagi University of Education

Y. Fukuda

Kamioka Observatory, ICRR, Univ. of Tokyo S. Moriyama, K. Hiraide
University of Fukui I. Ogawa
Tokyo University of Science

T. GunjiInstitute for Materials Research, Tohoku University S. Kurosawa

Conceptual design of ZICOS detector
Phys.Rev.Lett. 117 (2016) 082503

0𝜈𝜈
NEMO3 : 𝑇𝑇1/2> 9.1 × 1021 yrs

96Zr : 45 kg (nat.) → 865 kg(50 % enrich)→1/20 BG

0𝜈𝜈
𝑇𝑇1/2> 4 × 1025 yrs → 2 × 1026 yrs → ~1 ×1027yrs

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Observation of 2νββ events using 96Zr
• 16 cm diameter roundbottom flask using Ultrapure quartz.
• 20 low ＢＧ 2” PMT
Hamamatsu H3378-50.
• Designed mounting jig• Filled 1.0L of ZICOS
liquid scintillator loaded
100g of Zr(iPrac)4 whichcontains 0.4 g of 96Zr.
• Expected number ofevents is ~100 per year.
• LAB-A in Kamioka mine
XVIII International Conference on Topics in Astoparticle and Underground Physics(TAUP2023)

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Underground laboratory in Kamioka mine

LAB-A : Behind of LINAC control room
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Background estimation
U/Th in GE214 using ICP Mass spectrometer :232Th : 15ng/g corresponds to 6.09×10-5Bq/g
238U : 29ng/g corresponds to 3.58×10-4Bq/g
40K : 0.021ng/g corresponds to 5.59×10-6Bq/gAssuming radiation (perpetual) equilibrium :λANA=λBNB (Decay rate should be same)
The detector flask uses 530g of GE214.
208Tl : 1017908 events per year
214Bi : 5988404 events per year
will occur.
40K : 93556 events per year
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Monte Carlo simulation assuming ETFE bag•

40K affects only part of2νββ observation.
• 214Bi is significant BG,
but small fraction of2νββ events should beobserved.
• 208Tl is most serious BGfor 2νββ. A few eventsmight be observed.
Need tuning for inner
ETFE cubic bag forliquid scintillator.
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Present status• Clean booth (class 1000) was constructed for
preparation of Liquid Scintillator and detector.
• 200g of Zr(iPrac)4 is ready. Stored in the dry box.
• 20 Hamamatsu H3378-50 PMTs will be ready at nextmonth.
• Round bottom flask using GE214 is ready. Stored inthe clean room
• Inner bag stored for liquid scintillator will be preparedby ETFE sheet. No damage was found.
• We measured the transparency of ETFE sheet using
scintillation and obtained 2.5% loss at maximum.
• Centrifuge for 96Zr isotope separation was proposed
to JNFL and 25% enrichment maybe possible.
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Clean booth and 200g Zr(Iprac)4• Glove box with N2 gas circulation has been installed.
• 200g Zr(iPrac)4 was stored in dry box.
• 12 Hamamatsu H3378-50 are ready. 8 PMT will bedelivered at next month.
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Present status• Clean booth (class 1000) was constructed for
preparation of Liquid Scintillator and detector.
• 200g of Zr(iPrac)4 is ready. Stored in the dry box.
• 20 Hamamatsu H3378-50 PMTs will be ready at nextmonth.
• Round bottom flask using GE214 is ready. Stored inthe clean booth. PMT mounting jig is also designed .
• Inner bag stored for liquid scintillator will be preparedby ETFE sheet. No damage was found.
• We measured the transparency of ETFE sheet using
scintillation and obtained 2.5% loss at maximum.
• Centrifuge for 96Zr isotope separation was proposed
to JNFL and 25% enrichment maybe possible.
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August 29,2023

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Ultra-pure quartz flask and inner bag• Ultra-pure quartz round flask is ready.
• We will use ETFE sheet for inner bag. No damage
due to Anisole erosion was found within one month.
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Present status• Clean booth (class 1000) was constructed for
preparation of Liquid Scintillator and detector.
• 200g of Zr(iPrac)4 is ready. Stored in the dry box.
• 20 Hamamatsu H3378-50 PMTs will be ready at nextmonth.
• Round bottom flask using GE214 is ready. Stored inthe clean room.
• Inner bag stored for liquid scintillator will be preparedby ETFE sheet. No damage was found.
• We measured the transparency of ETFE sheet using
scintillation and obtained 2.5% loss at maximum.
• Centrifuge for 96Zr isotope separation was proposed
to JNFL and 25% enrichment maybe possible.
XVIII International Conference on Topics in Astoparticle and Underground Physics(TAUP2023)

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Measurement of transparency for ETFE sheet• Transparency of ETFE sheet using Liquid Scintillator.
• Compered peak value of some RIs for side PMTs
w/wo ETFE sheet covered side wall of vial.
• Bottom PMT was always without ETFE sheet.
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For bottom PMT1.0015± 0.0018

Same LY as expected

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For side PMTs

0.9768 ± 0.0014

2.5% loss at maximum

XVIII International Conference on Topics in Astoparticle and Underground Physics(TAUP2023)

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Present status• Clean booth (class 1000) was constructed for
preparation of Liquid Scintillator and detector.
• 200g of Zr(iPrac)4 is ready. Stored in the dry box.
• 20 Hamamatsu H3378-50 PMTs will be ready at nextmonth.
• Round bottom flask using GE214 is ready. Stored inthe clean room.
• Inner bag stored for liquid scintillator will be preparedby ETFE sheet. No damage was found.
• We measured the transparency of ETFE sheet using
scintillation and obtained 2.5% loss at maximum.
• Centrifuge for 96Zr isotope separation was proposed
to JNFL and 25% enrichment maybe possible.
XVIII International Conference on Topics in Astoparticle and Underground Physics(TAUP2023)

August 29,2023

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Centrifuge plant of JNFL at Rokkasho-village

https://www.jnfl.co.jp/ja/business/about/uran/summary/development-center.html
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96Zr isotope separation by Gas Centrifuge

JNFL staffs of TechnicalDevelopment Center for
Uranium Enrichment arelooking for new idea forisotope separation using
their Centrifuge plant.
Proposed 96Zr separation
using ZrCl4 (bp 331 ℃) :Need new sublimationpressure data.

XVIII International Conference on Topics in Astoparticle and Underground Physics(TAUP2023)

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96Zr isotope separation by Gas Centrifuge

JNFL staffs of TechnicalDevelopment Center for
Uranium Enrichment arelooking for new idea forisotope separation using
their Centrifuge plant.
Proposed 96Zr separation
using ZrCl4 (bp 331 ℃) :Need new sublimationpressure data.
25% enrichment maybe
possible by gas centrifuge.
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Future plan
• Preparation of ZICOS liquid scintillator will start soon.
• Radiation shielding using Pb blocks with fallingprevention wall is designed . Inner size could be
80cm cubic.
• Tuned inner bag using ETFE sheet will be readyafter welding test by company.
• Mockup for PMT mounting jig with flask will be doneat early next year.
• Installation of inner bag and bringing of LS will betested by using ultra-pure water after the mockup.
• Construction of Pb shield and 2ν-ZICOS detector will
start at next fiscal year in LAB-A.
• Observation will start in next summer. Stay tuned!
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backup

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Zr loaded liquid scintillator
2017

2013~2015
2015
Measured on this August.
An energy resolution is obtainedby 2.61±0.14% at 3.35 MeV
assuming 64% photo coverageof the photomultiplier.
日本物理学会2017年秋季大会

2017年9月13日∆𝐸𝐸= 0.125
𝐸𝐸(𝐸𝐸 = 1.02MeV)

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ZICOS- Zirconium Complex in Organic
Liquid Scintillator for next generation of0𝜈𝜈
NEMO3 : 𝑇𝑇1/2> 9.1 × 1021 ys
DBD experiment

96Zr : 45kg (nat.) → 865kg(50% enrich)0𝜈𝜈0𝜈𝜈
> 4 × 1025 ys →𝑇𝑇1/2> 2 × 1026 ys
𝑇𝑇1/2

日本物理学会2017年秋季大会

2017年9月13日

22Experimental site in LAB-A

Need to apply inner-University Research Program

XVIII International Conference on Topics in Astoparticle and Underground Physics(TAUP2023)

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U/Th/K contamination in material
Goal : U/Th ~1ng/g

Most serious BGs come from Ultra pure quartz.
XVIII International Conference on Topics in Astoparticle and Underground Physics(TAUP2023)

August 29,2023

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Discrimination of signal and BG
0νββ event
e-Reconstructed vertex byescintillation light

β decay
2.6 MeV γ
Reconstructed vertex
by Cherenkov light
Balloon or
surface ofdetector
XVIII International Conference on Topics in Astoparticle and Underground Physics(TAUP2023)

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Demonstration of 208Tl background
reduction using Cherenkov lights
1. Selection of PMTs which receive Cherenkov
lights among huge Scintillation lights.
• Pulse shape discrimination
2. Confirm topology of Cherenkov lights• Directionality of Cherenkov lights• Direct measurement of topological information
as an averaged angle
3. Demonstrate BG reduction using beta-gamma
sources with topological information (averagedangle) of Cherenkov light.
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Demonstration of 208Tl BG reduction using
UNI-ZICOS detector

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Setup for measurement with UNI-ZICOS

Source holder has
a hole, and it canbe covered by Al
plate (0.3mm and2mm) to terminate
betas.
The vertex position could be reconstructed by assuming that all PMTs should havesame effective charge which is corrected by the distance between PMT and vertex.
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Events selection for β+γ rich samples(Al 2mm)(Al 2mm)γ events(E<1.48MeV)(Al 2mm)γ events

γ events(E<1.48MeV)

γ events

XVIII International Conference on Topics in Astoparticle and Underground Physics(TAUP2023)(Al 2mm)(E<1.48MeV)

August 29,202329

Observed averaged angle using β−γ events•••••

0.3mm Al plate terminates β(E<0.3MeV) events.
Small difference between 2mm Al
on and off
Obtained averaged angle has
small peak around 60 deg.
There is no clear source to explain
around 40 deg events.
MC(β(E<1.48MeV) + γ ) looks
reproduce higher peak.

Averaged angle could be usedfor reduction of β + γ events
such as 208Tl decay background.
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Observed averaged angle using β−γ events• Clear averaged angle of β +γ events is obtained bysubtraction of those data.
• Obtained averaged angle
has a peak around 58 deg.
• Averaged angles ofMC(β(E<0.3MeV) + γ)
reproduce peak, but not
reproduce shape.
• Averaged angle ofMC(β(E<1.48MeV) + γ) may
help to reproduce larger
angle shape.
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Pulse shape of Cherenkov and scintillation
arbitary scale• Pulse shape of 90Sr using
H2431-50 measured byV1751 with DES mode
(2GS/s)• Decay time of scintillation :4.57 ns and 8.38 ns• Rise time of scintillation :1.45 ns• Rise time of Cherenkov :0.75 ns
Use the charge ratio Qtime/Qtotal. Here, Qtimeis FADC
count in each time, and Qtotalis sum count of FADC
between 55 ns and 80 ns.
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Topological information of Cherenkov lights
Average direction =Σ- di (di : unit vector)
edi θi

Vertexposition

Averagedangle= Σ θi
Nhit
Topological information (averaged angle) of Cherenkov
lights should be different between β and β + γ event.
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Simulations and data for beta
• Beta MC
indicated poor
light yield todetect beta onlyevents.
• 90Sr real data
confirmed poor
light yield eventhough higher
energy than 60Co.
Still there is no clearsource to explain
around 40deg event.
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Observed averaged angle using FDFE events•••••

The vertex position was reconstructedby charge information as explained.
Extracted PMTs which include
Cherenkov light by PSD technique.
Using those PMTs and the vertex, theaveraged angle of fixed direction fixedenergy (1.484MeV) electron from 88Y
source was measured, and a peak
was found around 50 degree.
The averaged angle obtained by MCsimulation has a peak around 48degree. Within the statistical error, thepeak position was almost reproduced.
Measurement time was limited byMarch earthquake in Japan.

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Synthesis ofZr(iPrac)4
wassucceeded.
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Topological information of Cherenkov lights
Average direction =Σ- di (di : unit vector)
edi θi

Vertexposition

Averagedangle= Σ θiNhit
Topological information (averaged angle) of Cherenkov
lights should be different between 2νββ and β + γ event.
XVIII International Conference on Topics in Astoparticle and Underground Physics(TAUP2023)

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Topological information of Cherenkov lights

MC(β + γ ) does not reproduce thesmall bump around 40 degree.
They might be caused by beta onlyevents which don’t have enoughlight yield as indicated by MC. (atlast JPS)XVIII International Conference on Topics in Astoparticle and Underground Physics(TAUP2023)

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Results of test synthesis of Zr(iPrac)4 by NARD

ZrO2/Zr(iPrac)4=18.5%

Synthesis of Zr(iPrac)4was succeeded.

83.76%XVIII International Conference on Topics in Astoparticle and Underground Physics(TAUP2023)

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