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XX～ニュートリノの放出を伴う二重ベータ崩壊事象
観測実験の準備状況～
日本物理学会2023年春期大会

March 25, 2023

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. 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 2023年春期大会

Mar 25,2023

2

Measurement of averaged angle with UNI-ZICOS

MC(β + γ ) does not reproduce thesmall bump around 40 degree.
They might be caused by beta only
events which don’t have enoughlight yield as indicated by MC. (atlast JPS)
日本物理学会 2023年春期大会

Mar 25,2023

3

Simulations and data for beta• Beta MC
indicated poor
light yield todetect beta only
events.
• 90Sr real dataconfirmed poor
light yield eventhough higher
energy than 60Co.
Still there is no clear
source to explain
around 40deg event.
日本物理学会 2023年春期大会

Mar 25,2023

4

Observation of 2νββ events using 2ν-ZICOS

日本物理学会 2023年春期大会• 16 cm diameter roundbottom flask using Ultrapure quartz.
• 20 low ＢＧ 2” PMT
Hamamatsu H3378-50
and 12 low BG 1” PMTH6610.
• Filled 2.2L of ZICOS
liquid scintillator loaded
220g of Zr(iPrac)4 whichcontains 0.85 g of 96Zr
nuclei.
• Expected number ofevents is 200 per year.
Mar 25,20235Measurement of U/Th/K contamination
Goal : U/Th ~1ng/g

日本物理学会 2023年春期大会

Mar 25,2023

6Background estimation
ICP Mass spectrometry analysis results:
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)If the detector flask use 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 2023年春期大会

Mar 25,2023

7

Monte Carlo simulation• Decay of 40K does notaffect 2νββ observation.
• Decay of 214Bi hassignificant BGs for2νββ even if 1/10 level.
• Decay of 208Tl has mostserious BGs for 2νββeven if 1/10 level.
Need 1ng/g for U/Th cont.
for quartz and improvethe vertex reconstruction
method (or larger flask)
日本物理学会 2023年春期大会

Mar 25,2023

8

Present status• Small lot synthesis of Zr(iPrac)4 was succeeded byNARD. Over 200g has been ordered and it will bedelivered at the end of April.
• Clean booth (class 1000) was constructed for
preparation of Liquid Scintillator and detector.
• 8 PMTs of Hamamatsu H3378-50 will be deliveredat the end of this month.
• Test round bottom flask using GE214 has beenordered and it will be delivered at the end of thismonth. But need more clean quartz and larger flask.
• Vertex reconstruction method should be improved.
• Centrifuge for 96Zr enrichment has been discussed
by JNFL and 50% enrichment is not impossible.
日本物理学会 2023年春期大会

Mar 25,2023

9Synthesis ofZr(iPrac)4wassucceeded.
日本物理学会 2023年春期大会

Mar 25,2023

10

Present status• Small lot synthesis of Zr(iPrac)4 was succeeded byNARD. Over 200g has been ordered and it will bedelivered at the end of April.
• Clean booth (class 1000) was constructed for
preparation of Liquid Scintillator and detector.
• 8 PMTs of Hamamatsu H3378-50 will be deliveredat the end of this month.
• Test round bottom flask using GE214 has beenordered and it will be delivered at the end of thismonth. But need more clean quartz and larger flask.
• Vertex reconstruction method should be improved.
• Centrifuge for 96Zr enrichment has been discussed
by JNFL and 50% enrichment is not impossible.
日本物理学会 2023年春期大会

Mar 25,2023

11

Clean booth• Glove box with N2 gas circulation has been installed.
• Electrical balance was also installed in glove box.
• 8 Hamamatsu H3378-50, round bottom flask, andchemical storage for Zr(iPrac)4 will be installed.
日本物理学会 2023年春期大会

Mar 25,2023

12

Present status• Small lot synthesis of Zr(iPrac)4 was succeeded byNARD. Over 200g has been ordered and it will bedelivered at the end of April.
• Clean booth (class 1000) was constructed for
preparation of Liquid Scintillator and detector.
• 8 PMTs of Hamamatsu H3378-50 will be deliveredat the end of this month.
• Test round bottom flask using GE214 has beenordered and it will be delivered at the end of thismonth. But need more clean quartz and larger flask.
• Vertex reconstruction method should be improved.
• Centrifuge for 96Zr enrichment has been discussed
by JNFL and 50% enrichment is not impossible.
日本物理学会 2023年春期大会

Mar 25,2023

13

Present status• Small lot synthesis of Zr(iPrac)4 was succeeded byNARD. Over 200g has been ordered and it will bedelivered at the end of April.
• Clean booth (class 1000) was constructed for
preparation of Liquid Scintillator and detector.
• 8 PMTs of Hamamatsu H3378-50 will be deliveredat the end of this month.
• Test round bottom flask using GE214 has beenordered and it will be delivered at the end of thismonth. But need more clean quartz and larger flask.
• Vertex reconstruction method should be improved.
• Centrifuge for 96Zr enrichment has been discussed
by JNFL and 50% enrichment is not impossible.
日本物理学会 2023年春期大会

Mar 25,2023

14

Centrifuge plant of JNFL at Rokkasho-village

https://www.jnfl.co.jp/ja/business/about/uran/summary/development-center.html
日本物理学会 2023年春期大会

Mar 25,2023

15

96Zr enrichment by Gas Centrifuge

Meeting with JNFL staffs oftechnical development centerfor Uranium enrichment on
18th Nov.
They are looking for new
idea for isotope separation
using their Centrifuge plant.
Proposed 96Zr enrichment
using ZrCl4 (bp 331 ℃) :24-50% enrichment maybe
possible by gas centrifuge.
日本物理学会 2023年春期大会

Mar 25,2023

16

96Zr enrichment by Gas Centrifuge

Meeting with JNFL staffs oftechnical development centerfor Uranium enrichment on
18th Nov.
They are looking for new
idea for isotope separation
using their Centrifuge plant.
Proposed 96Zr enrichment
using ZrCl4 (bp 331 ℃) :24-50% enrichment maybe
possible by gas centrifuge.
日本物理学会 2023年春期大会

Mar 25,2023

17backup

日本物理学会 2023年春期大会

Mar 25,2023

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Topological information of Cherenkov lights
Average direction =Σ- di (di : unit vector)
edi θVertex
positioni

Averagedangle= Σ θiNhit
Topological information (averaged angle) of Cherenkov
lights should be different between 2νββ and β + γ event.
日本物理学会 2023年春期大会

Mar 25,2023

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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.
日本物理学会 2023年春期大会

Mar 25,2023

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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
日本物理学会 2023年春期大会

e-Mar 25,2023

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Pulse shape of Cherenkov and scintillation
arbitary scale• Pulse shape of 90Sr using
H2431-50 measured by
V1751 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.
日本物理学会 2023年春期大会

Mar 25,2023

22

Demonstration of 208Tl BG reduction using
UNI-ZICOS detector

日本物理学会 2023年春期大会

Mar 25,2023

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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%
日本物理学会 2023年春期大会

Mar 25,2023

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