Detecting Geoneutrinos Giorgio Gratta Physics Dept Stanford University An amateur’s primer in • the Earth sciences A little history of • Geoneutrino detection Basics of Neutrino • detection Results from KamLAND • and Borexino How to make further • progress (from the point of view of detection)
Structure of the Earth: a particle physicist’s view 35km From seismic data • 5 basic regions: - inner core, 6km - outer core, 2900km - mantle, - oceanic crust, - continental 2255km crust and sediments 1245km 6400km All these regions • behave like solids except the outer core. 2 Image by: FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos Colin Rose and Dorling Kindersley
Convection in the Earth Image: http://www.dstu.univ-montp2.fr/PERSO/bokelmann/convection.gif • The mantle appears to convect even though it is solid. • This is responsible for plate tectonics and earthquakes. • Oceanic crust is being renewed at mid-ocean ridges and recycled at trenches. 3 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
Francis Birch J. Geophys. Res. 57 (1952) 227 “Unwary readers should take warning that ordinary language undergoes modification to a high-pressure form when applied to the interior of the Earth. A few examples of equivalents follow: High-pressure form Ordinary meaning certain dubious undoubtedly perhaps positive proof vague suggestion unanswerable argument trivial objection uncertain mixture of all the pure iron elements 4 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
Very specific data on the Earth’s interior is hard to collect Historically, the only universal probe for the interior of the Earth has been seismology. But this is only sensitive to the elastic properties of the rocks. Nomenclature derives from the seismic boundaries. Composition is then guessed for the different regions that are assumed homogeneous in composition. Seismically motivated nomenclature is then used at times to signify a region of a certain composition. This is sometimes confusing. 5 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
OK, let’s say that the Earth probably has the same composition as the Solar System How to average over the Solar System? McDonough, Neutrino 2008 6 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
C1 chondrites have very similar composition to the solar photosphere (except for peculiar light elements that are expected to be anomalous around the Sun) 7 McDonough, Neutrino 2008 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
Next: McDonough, Neutrino 2008 1) Correct for the Relative Abundance loss of volatile elements during the Earth’s formation 2) Based on chemical affinity estimate the composition of different regions Core expected to have insignificant U, Th Independently know that U, Th are ~1000x more common in the crust (ppm) than in the mantle (ppb) 8 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
Only a shallow layer has been sampled for chemical composition by drilling/sampling - Deepest bore-hole (12km) is only ~1/500 of the Earth’s radius - Oceans and southern hemisphere substantially less studied 9 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
Q: What powers the Eyjafjallajökull? …more generally what powers plate tectonics and hence volcanoes? 10 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
Same boreholes can be used to measure the heat flow from the Earth’s interior • ∆ T hole is measured between 2 points far away along the borehole • Thermal conductivity C rock of the rock is measured in the lab • Q = ∆ T hole C rock (assuming pure conduction) • But in addition have to account for mantle convection • Get a total 46 3 TW (100 mW/m 2 ) • Error is small BUT other analyses with different convection model gives 31 1 TW (61mW/m 2 )… 11 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
Heat flow from the Earth Image: Pollack et. al Note the large emission under the mid ocean ridges (~83% of the total heat!): this is where mantle convects and this is also where the pure conduction model really does not work well. 12 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
Putting in context the 31-46TW produced by the planet Image: Pollack et. al From the Sun the Earth receives on average We need 15 TW to 1400W/m 2 at the top of the run human society. atmosphere and This is sizeable 400W/m 2 at the surface compared to the the surface temperature has total output nothing to do with the heath from the planet! produced inside. 13 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
What produces the heat ? Radiogenic heat / Total heat called “Urey ratio” believed to be 0.3 to 0.7 14 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
The 238 U long decay chain including β - decays 234 Th α 238 U 24.1d 4.5Gyr β 234 Pa 1.17min β 214 Pb α 218 Po α 222 Rn α 226 Ra α 230 Th α 234 U 27m 3.0m 3.8d 1.6kyr 77kyr 0.4Myr β 214 Bi 20m β 210 Pb α 214 Po 22yr 0.16ms β 210 Bi 5d β 206 Pb α 210 Po Stable 138d 15 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
The 232 Th long decay α 228 Ra 232 Th chain including β - decays 5.8yr 14Gyr β 228 Ac 6.2h β α α α α 212 Pb 216 Po 220 Rn 224 Ra 228 Th 11h 0.15s 56s 3.7d 1.9yr β α 208 Tl 212 Bi 0.36 3.1m 61m 0.64 β β 208 Pb 212 Po α Stable 0.3 μ s The 40 K β - decay 40 K 1.3Gy β EC 0.11 0.89 40 Ar 40 Ca Stable Stable FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos 16
ν e of different endpoint energy are emitted at each β - decay step producing characteristic spectra for 238 U, 232 Th (and 40 K) 17 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
…in the context of the other natural neutrinos… ~10 4 K.Scholberg, Neutrino2014 18 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
Pre-history of Geoneutrinos Fred Reines (?) working at a neutrino detector (circa 1953) 19 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
…Well… not quite ! ~30 TW That detector was some 5 orders of magnitude too small 20 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
Fast forward 45 years … 21 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
GeoNeutrino Timeline Pre-history: F.Reines’ & G.Gamov’s correspondence (1953) Early ideas: G.Eder, Nucl. Phys. 78 (1966) 657 G.Marx, Czech. J. Phys. B19 (1969) 1471 L.M.Krauss, S.L.Glashow, D.M.Schramm, Nature 310 (1984) 191 KamLAND proposal: P.Alivisatos et al, Stanford-HEP-98-03, Tohoku-RCNS-98-15 (1998) First experimental study (KamLAND): T.Araki et al., Nature 436 (2005) 499 Borexino enters the scene: G.Bellini et al. Phys. Lett. B687 (2010) 299 Latest KamLAND and Borexino results: A.Gando et al. (KamLAND), Phys. Rev. D 88 (2013) 033001 M.Agostini et al. (Borexino), Phys. Rev. D 92 (2015) 031101(R) …in addition there is now ample literature about the interpretation of the measurements (see later) 22 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
The process can be used to point at the Sun! Neutrino-Signal Angle relative to Sun 23 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
n γ 2200 keV e + γ 511 keV ν e γ 511 keV Large scintillator 10-40 keV 1800 keV vat E E E ( M M ) m E ν measurement 24 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos n n p e e The process has a 1.8MeV threshold: most of the flux is not accessible (no 40 K)
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Use inverse beta decay in liquid scintillator Artificial reactors are a nuisance as the spectrum partially overlaps Geoneutrinos are contained in the low energy part of the spectrum. 29 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
Nuclear reactors traditionally have been a substantial “background” to the Geoneutrino measurement in KamLAND Reactor + Backgrounds 0.9-2.6MeV time history +GeoNu model Reactor + backgrounds KamLAND Reactor only After the Fukushima accident this background has gone away 30 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
In order to help science and facilitate the study of GeoNeutrinos, Italy decided not to build new nuclear power plants and shut down the few they had! 31 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
Borexino GeoNu data is cleaner but statistics not as good as KamLAND (smaller detector) M.Agostini et al., Phys. Rev. D 92 (2015) 031101(R) GeoNeutrinos Null hypothesis excluded (3.6x10 -9 or 5.9 σ ) 32 FROST, Fermilab, Mar 2016 G.Gratta - Geoneutrinos
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