ジルコニウム96を用いたニュートリノを放出しない二重ベータ崩壊事象の探索XXI～2つのニュートリノを放出する二重ベータ崩壊事象の観測実験の準備状況～
日本物理学会 2024年春期大会

March 19, 2024

Grant-in-Aid for Scientific Research on Innovative Areas
19H05093 and 20H05241
Scientific Research (B) 22H01243

Miyagi University of Education Y. Fukuda, R.Sato, K.Sugawara,
K.Takemura, K.Toyama
Kamioka Observatory, ICRR, Univ. of Tokyo S. Moriyama, K. Hiraide
University of Fukui I. Ogawa
Tokyo University of Science T. Gunji
Institute 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

日本物理学会 2024年春期大会

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2

Observation of 2νββ events using 96Zr
• 16 cm diameter roundbottom flask using Ultrapure quartz (GE214).
• 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
日本物理学会 2024年春期大会

Mar 19,2024

3

Underground laboratory in Kamioka mine

LAB-A : Behind of LINAC control room
日本物理学会 2024年春期大会

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4

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/g
Assuming 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
日本物理学会 2024年春期大会

Mar 19,2024

5

BG simulation assuming ETFE cubic bag•

40K affects only part of2νββ observation.
• 214Bi is significant BG,
but small fraction of2νββ events should beobserved.
• 208Tl is most serious BG
for 2νββ. A few eventsmight be observed.
Need tuning for inner
ETFE cubic bag forliquid scintillator.
日本物理学会 2024年春期大会

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6

Present status• 2 Little of ZICOS Liquid Scintillator was prepared byunder graduated students for 4 months.
i. 10 wt.% for Zr(iPrac)4 into Anisole in the globe
box under N2 gas atmosphereii. 6 wt.% for PPO and 0.1wt.% for POPOP
iii. All procedures done in class 1000 clean room
using PFA SSC bottle.
• Prototype 10cm ETFE cubic bag was produced by
Taiyo Kogyo Corporation using 100µm film.
i. 5% light yield loss at maximum
ii. Size should be tuned (not suitable in the flask)• PMT mounting jig was prepared by CI corporation.
i. Need fitting to the flask (not a spherical shape)
日本物理学会 2024年春期大会

Mar 19,20247

Preparation of ZICOS liquid scintillator

日本物理学会 2024年春期大会

Mar 19,2024

8

Comparison of LY for ZICOS liquid scintillator

old LS

日本物理学会 2024年春期大会

new LSNo difference between
old liquid scintillator(Zr(iPrac)4 synthesizedby Prof.Gunji) and newliquid scintillator(Zr(iPrac)4 synthesizedby NARD)
9Mar 19,2024

Present status• 2 Little of ZICOS Liquid Scintillator was prepared byunder graduated students for 4 months.
i. 10 wt.% for Zr(iPrac)4 into Anisole in the globe
box under N2 gas atmosphereii. 6 wt.% for PPO and 0.1wt.% for POPOP
iii. All procedures done in class 1000 clean room
using PFA SSC bottle.
• Prototype 10cm ETFE cubic bag was produced by
Taiyo Kogyo Corporation using 100µm film.
i. 5% light yield loss at maximum
ii. Size should be tuned (not suitable in the flask)• PMT mounting jig was produced by CI corporation.
i. Need fitting to the flask (not a spherical shape)
日本物理学会 2024年春期大会

Mar 19,2024

10

ETFE cubic bag

日本物理学会 2024年春期大会

Mar 19,2024

11

Present status• 2 Little of ZICOS Liquid Scintillator was prepared byunder graduated students for 4 months.
i. 10 wt.% for Zr(iPrac)4 into Anisole in the globe
box under N2 gas atmosphereii. 5 wt.% for PPO and 0.2wt.% for POPOP
iii. all procedures done in class 1000 clean room
using PFA SSC bottle.
• Prototype 10cm ETFE cubic bag was produced by
Taiyo Kogyo Corporation using 100µm film.
i. 5% light yield loss at maximum
ii. Size should be tuned (not suitable in the flask)• PMT mounting jig was produced by CI corporation.
i. Need fitting to the flask (not a spherical shape)
日本物理学会 2024年春期大会

Mar 19,2024

12

Measurement of transparency for ETFE film

• Transparency of ETFE 100µm film using LiquidScintillator.
• Peak for 137Cs γ for PMTs covered side wall.
• Bottom PMT was always without ETFE film.
日本物理学会 2024年春期大会

Mar 19,202413

Light yield transparency of ETFE 100µm film

The transparencyof ETFE 100µm
thickness film isobtained asfollowing value:
0.9566±0.0027
5% loss at maximum

日本物理学会 2024年春期大会

Mar 19,2024

14

Present status• 2 Little of ZICOS Liquid Scintillator was prepared byunder graduated students for 4 months.
i. 10 wt.% for Zr(iPrac)4 into Anisole in the globe
box under N2 gas atmosphereii. 6 wt.% for PPO and 0.1wt.% for POPOP
iii. All procedures done in class 1000 clean room
using PFA SSC bottle.
• Prototype 10cm ETFE cubic bag was produced by
Taiyo Kogyo Corporation using 100µm film.
i. 5% light yield loss at maximum
ii. Size should be tuned (not suitable in the flask)• PMT mounting jig was produced by CI corporation.
i. Need fitting to the flask (not a spherical shape)日本物理学会 2024年春期大会

Mar 19,2024

15

PMT mounting jig

日本物理学会 2024年春期大会• Aluminum was used
for all materials.
• Support jig for PMT
inserted via chimney
was made by POM.
• Need fitting to theflask
16
Mar 19,2024

Plans for near future• Pb block and oxygen free cupper for radiation shield
will be produced by CI corporation in this April.
• 9cm ETFE cubic bag will be prepared by Taiyo
Kogyo Corporation soon.
• All stuffs will be moved to Lab-A in Kamioka mine at
beginning of May.
• Build clean booth and setup the radiation shield inthe clean booth at that time.
• 2ν-ZICOS detector will be built in June.
• The pilot run including calibration and DAQ programwith unformatted data will be done in July - August.
• Physics run will start in September.
日本物理学会 2024年春期大会

Mar 19,202417

Pb and OFC shield

日本物理学会 2024年春期大会

Mar 19,2024

18

Plans for near future• Pb block and oxygen free cupper for radiation shield
will be produced by CI corporation in April.
• 9cm ETFE cubic bag will be prepared by Taiyo
Kogyo Corporation soon.
• All stuffs will be moved to Lab-A in Kamioka mine at
beginning of May.
• Build clean booth and setup the radiation shield in
the clean booth at that time.
• 2ν-ZICOS detector will be built in June.
• The pilot run including calibration and DAQ programwith unformatted data will be done in July - August.
• Physics run will start in September.
日本物理学会 2024年春期大会

Mar 19,2024

19

backup

日本物理学会 2024年春期大会

Mar 19,2024

20

Observation of 2νββ events using 2ν-ZICOS• 16 cm diameter roundbottom flask using Ultrapure quartz.
• 20 low ＢＧ 2” PMT
Hamamatsu H3378-50.
• Filled 1 Little of ZICOS
liquid scintillator loaded
100g of Zr(iPrac)4 whichcontains 0.5 g of 96Zr
nuclei.
• Expected number ofevents is 100 per year.
日本物理学会 2024年春期大会

Mar 19,2024

21

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

β decay
2.6 MeV γ
Reconstructed vertex
by Cherenkov light
Balloon orsurface ofdetector
日本物理学会 2024年春期大会

e-Mar 19,2024

22

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

ZrO2/Zr(iPrac)4=18.5%

Synthesis of Zr(iPrac)4
was succeeded.

83.76%
日本物理学会 2024年春期大会

Mar 19,202423