Frontier of Understanding Earth’s Interior and Dynamics
Aug 8-9, 2022, in Sendai

Ocean Bottom Detector:
frontier of technology for understanding
the Mantle by geoneutrinos
Hiroko Watanabe
for the OBD working group*

Research Center for Neutrino Science, Tohoku University, Japan* K. Inoue1, T. Sakai1, H. Watanabe1, W. F. McDonough1,2,3, K. Ueki4, N. Abe4, M. Kyo4, N. Sakurai4, E. Araki4, T. Kasaya4, H. Yoshida4
1. Research Center for Neutrino Science, Tohoku University
2. Department of Earth Science, Tohoku University
3. Department of Geology, University of Maryland4. JAMSTEC (Japan Agency for Marine-Earth Science and Technology)

1/15Geoneutrinos
地球内部に含まれる放射性物質も、ベータ崩壊をElectron-antineutrinos from natural radioactive decays

して反電子ニュートリノを放出する。

¯e 4.1 ⇥ 10 /cm /sec

β-decay2

sha1_base64="(null)">(null)</latexit>

sha1_base64="(null)">(null)</latexit><latexit

sha1_base64="(null)">(null)</latexit><latexit

sha1_base64="(null)">(null)</latexit><latexit

232
208
232
Th !
Pb + 6Th(e.g. KamLAND)

40

UUThThTh

Energy threshold, 1.8 MeVinverse
β-decay
ウラン、トリウム、カリウムなどは崩壊によってエネルギーを生成し、反電子Eth = 1.8 MeV+10⌫¯+p!
e+n
238
e
ニュートリノも放出するので、反ニュートリノ流量から熱生成量がわかる。
238UUseries
series
232

ThTh
UTh series
232Th
series* Only geo-neutrinos from U and Th
Th
140K
カムランドは、ウラン、トリウムからの反電子ニュートリノに感度がある。

10−1

Th

Ca + e + ¯e + 1.311 MeV (89.28%)

sha1_base64="Hx4/iWlDJP8ufVN+C3plaw4I4NE=">AAACDHicbVC7SgNBFJ2NrxhfUUtFBoMgBMJuLLQM2lgmYB6QjWF2cpMMmZ1dZmaVsKS0sPFXbCwiYusH2PkN/oSzSQpNPDBwOOdc7tzjhZwpbdtfVmppeWV1Lb2e2djc2t7J7u7VVBBJClUa8EA2PKKAMwFVzTSHRiiB+B6Huje4Svz6HUjFAnGjhyG0fNITrMso0UZqZ3OuR2TsimjUBpzHIXYl6/U1kTK4x3Ab50f5JGUX7AnwInFmJFc6HFe+H47G5Xb20+0ENPJBaMqJUk3HDnUrJlIzymGUcSMFIaED0oOmoYL4oFrx5JgRPjFKB3cDaZ7QeKL+noiJr9TQ90zSJ7qv5r1E/M9rRrp70YqZCCMNgk4XdSOOdYCTZnCHSaCaDw0hVDLzV0z7RBKqTX8ZU4Izf/IiqRULzlmhWDFtXKIp0ugAHaNT5KBzVELXqIyqiKJH9IzG6NV6sl6sN+t9Gk1Zs5l99AfWxw/Etp5/</latexit>

ThK!

40+ 4e + 4¯
⇥e + 42.7 MeV<latexit

Th

Luminosity [/s/MeV]

Th

Th+ 6e + 6¯
⇥e + 51.7 MeV

UAnti-neutrino Detector

Thgeo-neutrinos

238
206
238
U!
Pb + 8<latexit

610−2K40

are detectable right now* 40K geo-neutrino detection needs
2005年には、地球反ニュートリノを観測できることを実証
KamLAND collaboration, “Experimental investigation of geologically
producedantineutrinos with KamLAND”
anothertechnology.
Nature 436, 03980 (2005)
90.5

11.5

22.5

33.5

Antineutrino Energy [MeV]Th

Number of geo∝

amount of U Th , radiogenic heat

2/15

Why geo-neutirno?: Big questions
What is in the mantle?
Many seismically imaged structures andchemical heterogeneities in the mantle

How much fuel is left to drive Plate Tectonics?
surface heat flow : 46 ± 3 TW

TotalCo(Continental Crust + Mantle)

10 TW

High Q

Middle Q

20 TW

Continental Crust

nt

Total

Low Q

Th/U = 3.9
K/U = 1.4 × 104

ineM

nt

antle

alCrus??

t?

30 TW
MantlePrimordialRadiogenic

6.8 TW

Geo-neutrino can directly define power to drive the Earth’s engine

Neutrino Geoscience: Current and Future

3/15

what we need
improved accuracy ofmulti-sitemeasurement
measurement&modelling

directional sensitive detector
new type detector

detector in the Ocean
current generation

total radiogenic heatin the Earth
Th/U
ratio
yltceriDnext generation
Measuring

resolving vertical andhorizontal flux differences

Measuring Next Target!

distinguishing mantle
contribution

Measuring

what we learn
first measurement in 2005

detecting
K geo-neutrino

OBD: breakthroughbeyond modern land-based detectortransforming our vision of deep Earth0020406080 100 120 140 160 180!e4/15Directionality

図 3.9: ニュートリノのエネルギーと陽電子、中性子の反跳角の相関 : 3MeV 以下の時中性子の反跳角は 35◦ 以下に抑えることが出来る。

of Liquid Scintillator

delayed : neutron capture signal

Neutron has directional information of anti-neutrino

Li loaded liquid scintillator

PRD 60, 053003 (1999), P. Vogel & J. F. Beacom

illator+eMeV)νeθn!n(0.511MeV)

P

Q=4.8MeVee

5.0MeV

8MeV
3.0MeV50

θe40

5MeV

Geo Anti-Neutrino DirectionEνegeo-neutrino angular
distribution @Kamioka
θnn30

θn 3H3MeV20n
ΔT=20µsec
6Li(0.15wt%)
αdelayed signal

1002MeV
110Pνe

2.0MeV(0.511MeV)e+θe

E" 8.0MeV

102

Neutron Kinetic Energy[keV]

Flux[cm2/sec/sr]

prompt signal

60dnUpperContinental
Crust
delayed signal
P
Lower Continental Crust

detector(2.2MeV)!

Oceanic Crust
Upper Mantle

coreU

Lower Mantle<3MeV→θ
n<35°Eνe
図 3.10: ニュートリノのエネルギーと中性子の運動エネルギー、反跳角の相関 : 3MeVThmantle

以下の時中性子の運動エネルギーは十数 keV 以下である。

ction of neutron Improvement
ure nucleus

1.minimize the thermal
610
dates: Li, B

diffusion
neutron2.α-ray
can’t
travellongcross 6section
Li loaded liquid scintillator

eactionforward recoil neutron retains
information of the anti-neutrino direction
Directional measurement of geo-neutrino flux from crust, mantle, and core
8

Tomography of earth’s deep interior by neutrinos→completed!

high vertex resolution detector →ongoing
11

Zenith Angle[deg]Current : KamLAND Latest Results

5/15

Accepted by GRL, “Abundances of uranium and thorium elements in Earth estimated by geoneutrino spectroscopy” (arXiv link)

reactor neutrino

low-reactor period
geo-neutrino

Dataset : Mar, 2002-Dec, 2021
Livetime : 5227 days
(low-reactor phase : 2590 days)

massive dataset of low-reactor period→ precise measurement of U and Th contributions

sha1_base64="9s1vNbVnVnK3oXx2lIDFJHgDvEo=">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</latexit><latexit

sha1_base64="ddo9njUPiF3O4++etxw1xfZnCsc=">AAAC8XichVJNa9swGJa9j3bZV9oeexELgw46Y4fQ7TIo66XHFPJRiL0gK3IiKslGkgdB6F/s0sNG6XX/Zrf+m8quM9I2bC8IPXre5/3QK6UFo0qH4Y3nP3n67PnW9ovWy1ev37xt7+yOVF5KTIY4Z7k8T5EijAoy1FQzcl5IgnjKyDi9OKn84+9EKpqLgV4WJOFoLmhGMdKOmu54WyausxhJZvbsW8yRXkhuhoeDhZ2uThwJl9la+AUerPQpK4mN+wt6P8Z+bAQTOU8TEwZHobPoMAx61d51oFszG2L/1sOyVNraD+u9xZlE2KwU/+91TfqPSiu1nbY7YRDWBh+DqAEd0Fh/2v4Tz3JcciI0ZkipSRQWOjFIaopdxlZcKlIgfIHmZOKgQJyoxNT3sfC9Y2Ywy6VbQsOaXY8wiCu15KlTVo2qh76K3OSblDr7nBgqilITge8KZSWDOofV88MZlQRrtnQAYUldrxAvkJusdp+k5YYQPbzyYzDqBtFR0DvrdY6/NuPYBvvgHTgAEfgEjsEp6IMhwJ7wfng/vV++8i/9K//6Tup7TcweuGf+71vxA/Io</latexit><latexit

Current : KamLAND Latest ResultsmodelsHighQ
MiddleQ
LowQ

best-fit

Th/U freeUTh
U+Th
117+41-39
58+25-24
174+29-28
3.3σ
2.4σ
8.3σ

Crust estimation

central value : Enomoto 2007
uncertainty : Rudnick&Gao 2014
Th/U ratio : Wipperfurth et al 2018

Radiogenic heatfrom mantle

crustal contribution

central value : Enomoto 2007
uncertainty : Rudnick&Gao 2014
Th/U ratio : Wipperfurth et al 2018

Conversion coefficients
between flux andradiogenic
heat in homogeneous mantle

6/15

U,Th
dQ
U,Th
U,Th
KamLAND result
U,ThmantleQ=()
Accepted by GRL, “Abundances of uranium and thorium elements in Earth estimated by geoneutrino
spectroscopy”(arXiv link)crustmantle
d U,Thmantle

measured flux
at the surface

Radiogenic Heatflux estimate incrustal model

Th/U free

Adding heat estimate from crust,
238U : 3.4 TW, 232Th : 3.6 TW

QU = 3.3+3.2
0.8 TW

QTh = 12.1+8.3
8.6 TW

QU + QTh = 15.4+8.3
7.9 TW

U, Th heat separated
measurement achieved

Model Rejection

HighQ model is rejected at
99.76 % C.L. (homogeneous mantle)
97.9% C.L. (concentrated at CMB)

N of event 0signal
rejection

Improve the distinct spectroscopic contributions of U and Th

20Multi-site Measurement+OBD
0107/15

Observation = Crust + Mantle

Near Future…

3 multi-site measurements canconstrain mantle contribution.
Crust estimation needs to be accurate.

+ OBD

OBD can directly measure
mantle contribution.

Observation(y = x + b)

Simulated measurement: Total geonu in TNU

TNU: anti-neutrino events seen by a kiloton detector in a year

Outlook toward year 202560

Šrámek et al. , S. Rep. 33034 (2016)

50Jinping

SNO+
Borexino
JUNO
KamLAND

403025% uncertainty
OBD by 1.5 kt x 3years

20

TW radiogenic
power in BSE(assuming Medium-Q model)

30

Mantle10Mantle

Medium−Q

20

Low−Q
1000

2.3

10

20

30

40

5060

Geophysical prediction: Lithospheric flux in TNU

Crust

8/15

OBD Motivations• Direct Measurement of MantleŠrámek et al (2013) EPS, 10.1016/j.epsl.2012.11.001

Mantle/Total

need to be far from crust
can be far from reactors• Multi-site Measurements
Solve the mystery of deep Earth!
First detector for mapping the inhomogeneous mantle

OBDOBD

3%

10%

12%

13%15%70%

Mantle Crust (global)

合計への寄与contributions [%]• Multidisciplinary Detector

antineutrinos [TNU]

Reactor Crust (<500km)

9/15

OBD Motivations• Direct Measurement of MantleŠrámek et al (2013) EPS, 10.1016/j.epsl.2012.11.001

Mantle Geoneutrino Flux

need to be far from crust
can be far from reactors• Multi-site Measurements①

Solve the mystery of deep Earth!
First detector for mapping the inhomogeneous mantle• Multidisciplinary Detector

Seismically slow “red” regions in the deep mantle②site 1High QMiddle Q

From Alan McNamara after Ritsema et al (Science, 1999)

Low Q

site 2

OBD Motivations• Direct Measurement of Mantle
need to be far from crust
can be far from reactors• Multi-site Measurements
Solve the mystery of deep Earth!
First detector for mapping the inhomogeneous mantle• Multidisciplinary Detector
Physics, Geoscience, Mantle drilling, Biology, New technology,…

Physics :- multi baseline measurement of reactor neutrinos- astro particle physics- dark matter measurement with less-neutron background
etc.

10/15

11/15

OBD Present & Future
2005

No progress…

2019fund2020-2022 ed

we areehre~20 kg“Hanohano”
10~50 kT
1~5 kmwemovable

2005
45m

1-10 t~1.5 kt

10-50 kt

*OBD project has started with JAMSTEC &Tohoku U.!
* Japan Agency for Marine-Earth Science and Technology

26mJuly 9, 2019
Vessel : 112m × 32m

U. Hawaii & Makai Ocean Engineering
Technical tests and detector design

Joint workshop on OBD with Ocean Engineering,
Earth Science and Neutrino Physics

12/15

OBD Present & Future
2005

No progress…

2019

fund
2020-2022 ed

we areehre~20 kg

1-10 t~1.5 kt

Technical test & world’s first measurement in the ocean with LS detector* Install detector into ~1km seafloor (JAMSTEC’s Hatsushima Observatory), takedata for several months* measure muon late in the sea → input parameter for future large detector* Technical developments are in progress.
Hatsushima Observatory
electrical & optical connections to near coast, monitor
cameras, etc.

detector design

10-50 kt

13/15

OBD Present & Future
No progress…

2005

fund
2020-2022 ed

reehrewe a2019~20 kg1-10 t10-50 kt

~1.5 kt

Maturity of science

Technical demonstration & environment measurement in the sea
deep sea neutrino & muon flux, ocean water density & temperature, radioactivity→ input parameters for ~1.5 kt detector designFirst clear mantle signal

T. Sakai, Poster

2.5

2.5

* Hawaii is possible position.
* Detector should be installed at ~4km deep sea toshield muons Low temperature (2-4℃)
high pressure (40MPa)

UTh

Total

Reactor

Acci.

(α,n)

6.59 1.64 8.23
Geo-nu (4.61) (1.15) (5.76)

4.13

1.92

3.88

AllTotal
UTh
Reactor neutrino
Total
AccidentalU(α,n) Th1.511.53

1.90

Stainless tankOD PMT

Buﬀer oil

ID PMT

Acrylicvessel

LS

1.5

1

0.5

00.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

Visible energy[MeV]

Accidental
Reactor neutrinoalpha,nBackgrounds

SignalE reagion

2Counts /0.1MeV/year* Detector simulation study is in progress.

Counts /0.1MeV/year2

He-Li Fast-neutron Total 0.5

2.96(mantle)* Mantle geoneutrino sensitivity

00

<2.42
<0.58

9.93
6.39

0

123

[Events/year]

highQ model:
1year → 3.7σ
middleQ model: 3year→ 3.5σ
lowQ model:
10year→ 2.5σ

45678

Visible energy[MeV]

ID PMT #3232
Placed inside thestainless tank

- 4 km deep sea
To reduce backgroundcaused by muons14/15

Technical Developments* PMT shieldref) IceCube experiment * Liquid scintillator

Needs : low backgroundpressure resistant

T. Sakai, Poster

LAB(oil) + PPO(fluorescents)
Low temperature

Acrylic- low background- pressure resistant : <40MPa broken

4℃ is brighter
thanplot20℃ (+9%)
LS Lightyield
ADC channel

light yield

1500
Temperature correction for PMT、3.8±1.2%

1400

1300

1200

4℃
20℃
20℃ KamLAND-LS

1100

can not be usedstructural calculation

Glass (OKAMOTO Glass Co.)- pressure resistant- very high impurities
238U

232Th

[g/g]
40K

* cleaner material selection* Pt coating on the melting pot

900

2

2.2

light transition

2.4

2.6

2.8

3

3.2

3.4

3.6
ppo[g/L]no temperature aﬀect
Transmittance [%]Pressure test @JAMSTEC

1000

160
140
120
100
80
60

target1x10-81x10-81x10-8normal glass~1x10-7~1x10-7~1x10-7

our work

1.4x10-8<5.0x10-93.4x10-9

reduction

1/10

1/500

1/300

40

enhance the size (20 inch)

200

can be used

300

350

400

450

500

550
600
WaveLength [nm]Technological development has been started!

Summary

15/15•
Geoneutrinos
areuniqueandnewtool
tomeasuredirectly
theEarth’sinterior.
• ‣Strong way to measure amount of radioactive elements in theFor two centuries we have asked what is the energy that drives the Earth?

•To date, physics experiments have shown the usefulness of geoneutrinos.
‣Interdisciplinary community has furthered its connection over these past 15 years.

•”Neutrino Geoscience” : collaborations between geology, physics and beyond‣Ocean Bottom Detector (OBD) = Breakthrough‣OBD has strong power to measure mantle contribution directly<Transformative insights>

OBD’s Primary Goal : •map the mantle•constrain the planet’s cooling history