ICEHAP Seminar

Ocean Bottom Detector:
Exploring the Mantle with geo-neutrinos

Hiroko Watanabe,
Research Center for Neutrino Science,
Tohoku University
November 1, 2024

Self-introduction!

1/38

Hiroko Watanabe
Research Center for Neutrino Science
Tohoku University
My research:*

Measuring neutrinos by KamLAND*“Neutrino Geoscience”: interdisciplinary science field→ Ocean Bottom Detector
KamLAND@KamiokaContents
1. Introduction
2. Experiments status
3. Exploring mantle
4. Ocean Bottom Detector
5. Summary

2/38

Contents
1. Introduction
2. Experiments status
3. Exploring mantle
4. Ocean Bottom Detector
5. Summary

2/38

3/38

Earth• Mass

6.0 x 1024 kg• Mean density

5,514 kg/m3• Mean radius

6,371 km• Elements
Fe, O, Mg, Si : ~94 %+ Ni, Ca, Al : ~99 %Moon scale to inner core

4/38

Earth’s Structure※ 40K, 232Th, 235U, 238U

① Crust : Solid (~99.5% of the Earth’s radiogenic heating power)- Volume : 2 %, Mass :~0.5※ %Seismic velocity structure

Volume3%2%
13%Heat-producing elements : 40 %- Changes of seismic wave and chemical composition
decide boundary

5100 km
6400 km 2900 km② Mantle : Solid- Volume : 82 %, Mass : 68%

Heat-producing elements : 60 %- Homogenous or Inhomogeneous? Chemical composition?

③ Outer Core : Fluid④ Inner Core : Solid- Volume : 16%, Mass : 32%

Heat-producing elements : negligible- Fe (+little Ni) Density : 10% lighter than Fe
40 km - Light elements? Amount?

82%
Mass

2% 0.5%30%
68%
Heat-producing
Elements

60% 40%5/38

Geo-neutrinos

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)

UTh

Th
Th

Th
Th

Th
U

Ca + e + ¯e + 1.311 MeV (89.28%)

Energy threshold, 1.8 MeV
inverseβ-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+n238e
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
seriessha1_base64="Hx4/iWlDJP8ufVN+C3plaw4I4NE=">AAACDHicbVC7SgNBFJ2NrxhfUUtFBoMgBMJuLLQM2lgmYB6QjWF2cpMMmZ1dZmaVsKS0sPFXbCwiYusH2PkN/oSzSQpNPDBwOOdc7tzjhZwpbdtfVmppeWV1Lb2e2djc2t7J7u7VVBBJClUa8EA2PKKAMwFVzTSHRiiB+B6Huje4Svz6HUjFAnGjhyG0fNITrMso0UZqZ3OuR2TsimjUBpzHIXYl6/U1kTK4x3Ab50f5JGUX7AnwInFmJFc6HFe+H47G5Xb20+0ENPJBaMqJUk3HDnUrJlIzymGUcSMFIaED0oOmoYL4oFrx5JgRPjFKB3cDaZ7QeKL+noiJr9TQ90zSJ7qv5r1E/M9rRrp70YqZCCMNgk4XdSOOdYCTZnCHSaCaDw0hVDLzV0z7RBKqTX8ZU4Izf/IiqRULzlmhWDFtXKIp0ugAHaNT5KBzVELXqIyqiKJH9IzG6NV6sl6sN+t9Gk1Zs5l99AfWxw/Etp5/</latexit>

U

Th

K!

40+ 4e + 4¯
⇥e + 42.7 MeV<latexit

Th

40

Luminosity [/s/MeV]

Th

Th+ 6e + 6¯
⇥e + 51.7 MeV

UAnti-neutrino DetectorTh

geo-neutrinos

238
206
238
U!
Pb + 8<latexit

6232

Th series
232Th
series* Only geo-neutrinos from U and ThTh
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。

10−110−2K40

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Geo-neutrino Energy

6/38

a few MeVIceCube

7/38

Earth’s Heat BudgetContributions

Surface heat flow

=Crust heat productionMeasuredTh

Th

Model

Radiogenic??

Primordial??

Radiogenic??

Primordial+
Mantle coolingTh

Source+Th

U

Mantle heat production

Th+UThThTh※

CMB heat flow

Th
ThTh
U

4100 K
5700 K
2730 K Th 1720 K

Core cooling + Inner core growth※Core Mantle Boundary

8/38

Earth’s Heat Budget
Contributions

Surface heat flow=

Crust heat production

Measured

Th

Th

Model

Radiogenic??

Primordial??

Radiogenic??

Primordial+
Mantle coolingTh

Source+Th

U

Mantle heat production

Th+UThThTh※

CMB heat flow

ThThThU4100 K
5700 K
2730 K Th 1720 KCore cooling + Inner core growthGeoneutrinos can define theamount of radiogenic heat※Core Mantle Boundary

Earth’s Heat Balance

9/38

Surface heat flow

46 ± 3 TW
exampleofEarthmodel
Earth’s surface heat flow 46 㼼 3 TW

crust heat flux measurement & calculation

imPr
diorMantle cooling(18 TW)al

Crust R*
(7 㼼 1 TW)

diog

total R*
20 㼼 4en

Mantle R*(13 㼼 4 TW)

icHe*R radiogenic heatat(after McDonough & Sun ’95)

tRaCore(~9 TW)

eaH(Rudnick and Gao ’03
Huang et al ‘13)-(4-15 TW)(0.4 TW) Tidal dissipation
Chemical differentiation

after Jaupart et al 2008 Treatise of Geophysics

Primordial Heat

* Releases of gravitational energy throughaccretion or metallic core separation* Latent heat from the growth of inner core

Rev. of Geophys. 31, 267-280 (1993)

Earth’s Heat Balance

10/38Surface heat flow

46 ± 3 TW
exampleofEarthmodel
Earth’s surface heat flow 46 㼼 3 TW
imPr
diorMantle cooling(18 TW)

alCrust R*(7 㼼 1 TW)

diogtotal R*
20 㼼 4enMantle R*(13 㼼 4 TW)

icHe*R radiogenic heatat(after McDonough & Sun ’95)

tRa

Core
(~9 TW)eaH(Rudnick and Gao ’03
Huang et al ‘13)-(4-15 TW)(0.4 TW) Tidal dissipation
Chemical differentiation

after Jaupart et al 2008 Treatise of Geophysics

Primordial Heat

* Releases of gravitational energy throughaccretion or metallic core separation* Latent heat from the growth of inner coreQ : How much radiogenic heat
contributes to Earth’s heat?

11/38

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 QMiddle Q

20 TW

Continental Crust

TotalLow Qnt

M

Th/U = 3.9
K/U = 1.4 × 104

aninetlentalCrus??

?

30 TWMantle

PrimordialRadiogenic

6.8 TWt

What we can learn

12/38

Nature & amount of Earth’s thermal power
1. abundance of heat producing elements (U, Th, K) in the Earth
2. clues to planet formation processes
3. amount of radiogenic power to drive mantle convection & plate tectonics
4. is the mantle compositionally layered or have large structures?

13/38What we can learn
Nature & amount of Earth’s thermal power

1. abundance of heat producing elements (U, Th, K) in the Earthestimates of silicate Earth 9-36 TW
2. clues to planet formation processes
constrains chondritic Earth models
3. amount of radiogenic power to drive mantle convection & plate tectonics
estimates of mantle 3.2-32 TW
4. is the mantle compositionally layered or have large structures?
layers, LLSVP*, super-plume piles*Large-Low-Shear-Velocity Provinces

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

Contents
1. Introduction
2. Experiments status
3. Exploring mantle
4. Ocean Bottom Detector
5. Summary

14/38

Experiments* Not yet reported

~2020

15/38
Finished
Running
Constructing
Planing

Two experiments have published geoneutrino measurement results.

KamLAND & Borexino#talks_react_geo_nus

10/36
16/38
7/27
4/15

Two liquid scintillator (LS) experiments have measured geoneutrinos.
KamLAND (Japan, 2002~)

Borexino(Italy,2007~)
Borexino(Italy,2007~2020)* LS : 1000 t* LS : 278 t* Depth : 2700 m.w.e.

* Depth : 3800 m.w.e.

* expected event ratio* expected event ratio

reactor/geo ~6.7 (up to 2010)~0.4 (2011~)
w/o Japanese reactors

reactor/geo ~0.3 (2007~)KamLAND Latest Results

17/38

S. Abe et al, “Abundances of uranium and thorium elements in Earth estimated by geoneutrino spectroscopy”, GRL, 49, e2022GL099566

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><latexitmodels
HighQ
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

sha1_base64="ddo9njUPiF3O4++etxw1xfZnCsc=">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</latexit>

U,Th
dQ
U,Th
KamLAND result
U,Th
mantle
QU,Th=()
mantleS. Abe et al, “Abundances of uranium and thorium elements in Earth estimated by geoneutrino spectroscopy”,
GRL, 49,cruste2022GL099566
d U,Thmantle<latexit

KamLAND Latest Results
Conversion coefficients
between flux andradiogenic
heat in homogeneous mantle

18/38

measured fluxat 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

19/38Borexino
Mantle only

Phys. Rev. D 101, 012009 (2020)

Fully Radiogenic

High Q
Middle Q
Low Q(Mantle, U+Th) 24.6 +11.1/-10.4 TW

Total radiogenic heat:High Q (30TW radiogenic hear) model is preferred.

Lithosphere Model
Distance and Cumulative Flux

20/38

Sammon, L. G. and McDonough, W. F., EPSL, 539, 117684 (2022)

×106

Total 100＜５００kmCrust 80５０％3602Mantle140

Percentage of total (%)

Cumulative flux (1/cm2/sec)

4

sediment
crustmantle
total

20

Sediment
0 01010

1neutrino oscillation
P (E, L) ⇠ 1

21010
Distance from KamLAND (km)1sin2 2✓12231040(constant suppression)

50% of the total flux originates within 500 km

NFLFFL(Borexino’s model)

Borexino’s model did not include the zero-age igneous rocks.
→ Low NFL → High mantle

Insights from geoneutrino experiments strongly depend on crustal models,
especially near Lithosphere models, around the detectors.

21/38SNO+
Measured anti-neutrino spectrum
from Ana Sofia Inácio’s slides presented at NeuTel2023

Information from I. Semenec and M. Chen

Expected event[TNU]* Crust 55.3±5.1* Mantle
LowQ 2.6±1.6
MidQ 8.4±2.8
HighQ 17.8±2.6

Crust ~80%
Crust
Mantle
Total
Oceanic

Mantle ~20%

* Scintillator was filled [PPO 0.6g/L(April-July 2021), 2.2g/L (April 2022-March 2023)]* Te will be added in 2024 for 0νββ measurement.
* Geo-neutrino measurement was started, and will continue after Te addition* Local geology around SNO+ site is well studies. Very old crust area.

First measurementin North America

22/38JUNO
Expected spectrum

Information from J. Cao

Expected event
38.7 TNU (408 events/year)
Backgrounds

Event rate/yearreactor

16100

9Li-8He20

fast neutrons

100

13C(α,n)16O50

accidental events

401
Han, Li, et, al. CPC 2016

Geological map
from Yury Malyshkin’s slides
presented at NeuTel2023

Challenges* Reactor neutrino background
Motivations* Distinguish U/Th signals, obtain ratio * Refined local crustal model* Extract mantle component* 2024~ data taking

Sensitivity: ~22% (1 year), ~8% (10 years)

Large statistics

Contents
1. Introduction
2. Experiments status
3. Exploring mantle
4. Ocean Bottom Detector
5. Summary

23/38

Neutrino Geoscience: Current and Future

24/38

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2025/38

Multi-site Measurement+OBD
010Observation = 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 2025

60Šrámek et al. , S. Rep. 33034 (2016)

50

Jinping

SNO+Borexino
JUNO
KamLAND

40

30

25% uncertainty
OBD by 1.5 kt x 3years

20TW radiogenic
power in BSE(assuming Medium-Q model)

30

Mantle10Mantle

Medium−Q

20Low−Q00

2.310203040

105060Geophysical prediction: Lithospheric flux in TNUCrust26/38OBD 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

OBD

OBD

3%

10%

12%

13%

15%

70%

Mantle Crust (global)

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

antineutrinos [TNU]

Reactor Crust (<500km)

27/38OBD 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 mantle②
site 1High Q

Middle 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,…

28/38

Contents
1. Introduction
2. Experiments status
3. Exploring mantle
4. Ocean Bottom Detector
5. Summary

29/38

30/38

OBD Present & Future
2005

No progress…

2019

fund
2020-2024 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

31/38

OBD Present & Future
2005

No progress…

2019

fund
2020-2024 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

32/38

OBD Present & Future
No progress…

2005

fund
2020-2024 ed

ree
h
re

we a

2019

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

Backgrounds

Signal
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

E reagion

All

1.53

1.90

2TotalUThReactor neutrino
Total
Accidental
UTh
(α,n)

1.5

1

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

Counts /0.1MeV/year

First clear mantle signal

2.52

Stainless tankOD PMTBuffer oil

ID PMT

Acrylicvessel

LS

1.5

10.5

00.8

11.2

1.4

1.6

1.8

2

2.2

2.4

2.6

Visible energy[MeV]

Accidental
Reactor neutrinoalpha,nHe-Li Fast-neutron Total 0.5

2.96(mantle)* Mantle geoneutrino sensitivity

00

<2.42
<0.58

9.93
6.39

0

12

3

[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33/38

OBD Present & Future
2005

No progress…

2019

fund2020-2024 ed

reehrewe a~20 kg

1-10 t10-50 kt

~1.5 kt

Community Building Status
Thematic Program 2022

international symposiums

Corporative study with U. Hawaii* discussing the plan for prototype detector deployment
in the ocean around Hawaii island* long-term stay at U. Hawaii for international/
interdisciplinary community building (Nov-Dec 2023)
未来の学術振興構想2023 (日本学術会議)

outreach @Astronomical Observatory
In total~60 participantsfrom different
countries during
the program.

…

34/38

Status of Technical Developments✦ PMT shield

IceCube type PMT
module is expected

Needs : low backgroundpressure resistant✦ Liquid scintillator

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 used?
structural calculation

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

232Th

[g/g]
40K

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

* 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 affectTransmittance [%]Pressure test @JAMSTEC

1000

160
140
120
100
8060

enhance the size (20 inch)

40
200

can be used

300

350

400

450

500

550600WaveLength [nm]

Status of Technical Developments

35/38✦ Liquid scintillator density under low-temperature & high pressure

Temperature & pressure dependence profiles are available.
uncertainty : 0.05%
atmospheric pressurepressure

2Temperature

Pressure

20℃, atmospheric pressure : 858.11 kg/m3

compensation volume

2℃, 10 MPa (1km seafloor) : 876.02 kg/m3 (calculated)+2.1% → 0.63 L for 30L LS

2℃, 40 MPa (4km seafloor) : 891.84 kg/m3 (calculated)+3.9% → 68 m3 for 1.5 kt LSStatus of Technical Developments✦ Prototype detector design & construction

36/38

stainless box

glass shield for Photomultiplier (PMT)ref) IceCube experiment

PMT & electronics

flame

Liquid Scintillator tank (V=30L)

shield folder

planning to deploy prototypedetector into ocean in 2024

37/38

Technical and Science Coevolution
2024~✦ Prototype detector (20kg) : our first experience deploying LS detector into the ocean@~1km, ~4℃, 10MPa* Technical items* workable PMT module in the ocean* remote control system (monitoring, DAQ)
* Science targets: muon rate & radioactivities in the ocean → input parameters for large size detector

around 2034~✦ Large size detector (1.5kt, 10-50kt) : first direct measurement of mantle geo-neutrino contribution@~4km, 2~4℃, 40MPa* Technical items:

Stainless tankOD PMT

Buffer oil

ID PMT

AcrylicvesselLS* PMT modules with shield* for inner detector: >3000, in buffer oil region* for outer detector: >300, in sea water (e.g. KM3Net)* low-power electronics* data transfer system* Science target:* mantle geo-neutrinos, high-energy neutrinos (OBD can use both water and LS as targets.)

ID PMT #3232
Placed inside thestainless tank

- 4 km deep sea
To reduce backgroundcaused by muonsSummary38/38•
Geoneutrinos
areuniqueandnewtooltomeasure
directly
theEarth’sinterior.
• ‣Strong way to measure amount of radioactive elements in the Earth
For 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 geoscience, physics, oceanengineering 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