1. Antineutrino, geoneutrinos and heat production in the Earth
Geophysics tells us where we are at today
Geochemistry tells us how we got there…
Geochemistry collaborator:
- Ricardo Arevalo : University of Maryland
Geoneutrino collaborators:
- John Learned : University of Hawaii
- Steve Dye: Hawaii Pacific University

2. 5 Big Questions: What is the Planetary K/U ratio?
Radiogenic contribution to heat flow?
Distribution of reservoirs in mantle?
Radiogenic elements in the core??
Nature of the Core-Mantle Boundary?
planetary volatility curve
secular cooling
whole vs layered convection
Earth energy budget
hidden reservoirs

3. AGE OF THE EARTH thermal evolution d = √pkt radioactivity John Perry
Heat loss depends on thermal boundary layer thickness d
John Perry
Lord Kelvin
1895
1862
d = √pkt d
Conductive cooling of a planet with a convecting interior
Conductive cooling of a solid planet
Age of Earth ~100 My
k =35 km2/My
Age of Earth ~1 Gy
radioactivity
“… Kelvin had limited the age of the earth provided that no new source of heat was discovered. … what we are considering tonight, radium!"
Rutherford fondly recalled, "Behold! the old boy beamed upon me.” (Kelvin was in the audience)
Ernest
Rutherford
1904

4. 1st order Structure of Earth Rock surrounding metal
Time Line
1st order Structure of Earth
Rock surrounding metal
1897
Emil Wiechert
1915
CORE-MANTLE
1925
UPPER-LOWER MANTLE
1935
INNER-OUTER CORE
PLATE TECTONICS
1970
1995

5. “Standard” Planetary Model
Chondrites, primitive meteorites, are key
So too, the composition of the solar photosphere
Refractory elements (RE) in chondritic proportions
Absolute abundances of RE – model dependent
Mg, Fe & Si are non-refractory elements
Chemical gradient in solar system
Non-refractory elements – model dependent
U & Th are RE, whereas K is moderately volatile

6. Meteorites Allende chondrites Johnstown Imilac Henbury
Achondrite, Ca-poor, Diogenite
Carbonaceous chondrite (CV3)
Imilac
Henbury
IIIAB
Meteorites
chondrites
Irons: pieces of core
Mantle-crust
pieces (?)
undifferentiated planets (?)
Pallasite: olivine and iron mixtures (CMB?)

7. “Standard” Planetary Model
Chondrites, primitive meteorites, are key
So too, the composition of the solar photosphere
Refractory elements (RE) in chondritic proportions
Absolute abundances of RE – model dependent
Mg, Fe & Si are non-refractory elements
Chemical gradient in solar system
Non-refractory elements – model dependent
U & Th are RE, whereas K is moderately volatile

8. C1 carbonaceous chondrite
Solar photosphere
(atoms Si = 1E6) B Li
C1 carbonaceous chondrite
(atoms Si = 1E6)

9. “Standard” Planetary Model
Chondrites, primitive meteorites, are key
So too, the composition of the solar photosphere
Refractory elements (RE) in chondritic proportions
Absolute abundances of RE – model dependent
Mg, Fe & Si are non-refractory elements
Chemical gradient in solar system
Non-refractory elements – model dependent
U & Th are RE, whereas K is moderately volatile

10. Th & U
Volatility trend
@ 1AU from Sun

11. 2 flashes close in space and time Rejects most backgrounds
Detecting
Geoneutrino
in the Earth
REFRACTORY ELEMENTS
b- decay
Detecting Electron Antineutrinos from inverse beta -decay
2 flashes close in space and time
Rejects most backgrounds
Nature 436, (28 July 2005)

12. MeV-Scale Electron Anti-Neutrino Detection
Key: 2 flashes, close in space and time,
2nd of known energy, eliminate background
Production in reactors
and natural decays
Detection
Evis=Eν-0.8 MeV
prompt
delayed
Evis=2.2 MeV
Standard inverse β-decay coincidence
Eν > 1.8 MeV
Rate and spectrum - no direction
Reines & Cowan

13. Radiogenic heat & “geo-neutrino”
K-decay chain
Detectable
>1.8 MeV
46%
31%
20% 1%
238U, 232Th and 40K generate 8TW, 8TW, and 3TW of radiogenic heat in the Earth
Th-decay chain
So, where does the heat come from? U, Th, and K inside the Earth are radioactive. As they and their daughter nuclei decay, they produce heat. According to the estimated amounts of U, Th, and K in the Earth, U decay chain produces 8TW, Th decay chain produces 8TW, and K decay produces 3TW of radiogenic heat, and the other long-lived radioactive isotopes contributions are negligible. --- These are the beta decays in the U, Th, and K decay chains. When they beta-decay, they produce electron antineutrinos.
Beta decays produce electron antineutrinos (aka “geo-neutrinos”)
U-decay chain
n p + e- + ne

14. Silicate Earth ? Normalized concentration Potassium in the core
REFRACTORY ELEMENTS
VOLATILE ELEMENTS
Allegre et al (1995), McD & Sun (’95)
Palme & O’Neill (2003) ?
Lyubetskaya & Korenaga (2007)
Normalized concentration
Potassium
in the core
Half-mass Condensation Temperature

15. Chromatographic separation Mantle melting & crust formation
U in the Earth:
~13 ng/g U in the Earth
Metallic sphere (core)
<<<1 ng/g U
Silicate sphere
20 ng/g U
Continental Crust
1000 ng/g U
Mantle
10 ng/g U
“Differentiation”
Chromatographic separation
Mantle melting & crust formation

16. Oceanic crust <<200 million years old

17. Continents up to 3500 million years old
ages
(Ga)
<0.6
>2.6

18. Earth’s Total Surface Heat Flow
Conductive heat flow measured from bore-hole temperature gradient and conductivity
Data sources
Total heat flow
Conventional view
463 TW
Challenged recently
311 TW
Source: International Heat Flow Commission web-site

19. after Jaupart et al 2008 Treatise of Geophysics

20. Urey Ratio and Mantle Convection Models
radioactive heat production
Urey ratio =
heat loss
Mantle convection models typically assume:
mantle Urey ratio: 0.4 to 1.0, generally ~0.7
Geochemical models predict:
mantle Urey ratio 0.3 to 0.5

21. Discrepancy? Est. total heat flow, 46 or 31TW
est. radiogenic heat production 20TW or 31TW
give Urey ratio ~0.3 to ~1
Where are the problems?
Mantle convection models?
Total heat flow estimates?
Estimates of radiogenic heat production rate?
Geoneutrino measurements can constrain the planetary radiogenic heat production.
Some mantle convection model suggests that the radiogenic heat produced should a larger fraction of the total heat flow. So at least one of the following have some problems: the total heat flow measured, the estimated amounts of U, Th or K, or the mantle convection model. So, by measuring the antineutrinos from beta decays of daughter nuclei in the U and Th decay chains, we can maybe serve as a cross-check of the radiogenic heat production rate.
chondritic meteorites -> 19TW, mantle convection model->more
>70% should be from radiogenic heat.
Need to subtract continental crust contribution (6.5TW) -> only ~35% (44TW) or ~51%(31TW).

22. -- models of mantle convection and element distribution
Mantle is depleted in some elements (e.g., Th & U)
that are enriched in the continents.
-- models of mantle convection and element distribution
Th & U
poor
Th & U
rich

23. Predicted Geoneutrino Flux irreducible background
Reactor Flux -
irreducible background
Geoneutrino flux determinations
-continental (KamLAND, Borexino, SNO+)
-oceanic (Hanohano)

24. Reactor Background
Reactor Background
with oscillation
Geoneutrinos
KamLAND
KamLAND was designed to detect reactor antineutrinos to measure the neutrino oscillation parameters. The picture shows the locations of KamLAND and all the nearby nuclear reactors. Nuclear reactors are indicated by the red-green dots. Naturally, the most significant background for geoneutrino detection is the antineutrinos from these reactors. The right plot shows the expected energy distributions of the geoneutrino spectrum and reactor background.
KamLAND was designed to measure reactor antineutrinos.
Reactor antineutrinos are the most significant background.

25. Continental Heat Flow : example from Canadian Shield
Perry et al (2006)
SNO+

26. Large liquid scintillation detectors used for measuring the Earth antineutrino flux
Borexino, Italy (0.6kt)
KamLAND, Japan (1kt)
SNO+, Canada (1kt)
Hanohano, US
ocean-based (10kt)

27. An experiment with joint interests in Physics, Geology, and Security
Hanohano
An experiment with joint interests in Physics, Geology, and Security
multiple deployments
deep water cosmic shield
control-able L/E detection
A Deep Ocean
e Electron
Anti-Neutrino
Observatory
Deployment Sketch
Descent/ascent 39 min

28. Summary of Expected Results Hanohano- 10 kt-yr Exposure
Neutrino Geophysics- near Hawaii
Mantle flux U geoneutrinos to ~10%
Heat flux ~15%
Measure Th/U ratio to ~20%
Rule out geo-reactor if P>0.3 TW
There is also plenty of Neutrino Physics..
And much astrophysics and nucleon decay too….

29. Published May 2008 Based on: R. de Meijer & W. van Westrenen
South African Journal of Science (2008)

30. Paramount Request Detecting Potassium (K) e
Significant for the Planetary budget of volatile element
-- What did we inherit from our accretion disk?
Fundamental to unraveling Mantle structure
-- 40K controls mantle Ar inventory 40K  40Ar (EC)
Geophysics want K in core to power the Geodynamo?
-- We don’t understand the energy source…