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

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

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

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

“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

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?)

“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

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

“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

Th & U Volatility trend @ 1AU from Sun

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, 499-503 (28 July 2005)

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

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

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

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

Oceanic crust <<200 million years old

Continents up to 3500 million years old ages (Ga) <0.6 06.-2.6 >2.6

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

after Jaupart et al 2008 Treatise of Geophysics

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

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).

-- 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

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

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.

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

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)

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

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….

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

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…