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July 21, 20081 Geoneutrinos Mark Chen Queen’s University OCPA Workshop on Underground Science Hong Kong, China.

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Presentation on theme: "July 21, 20081 Geoneutrinos Mark Chen Queen’s University OCPA Workshop on Underground Science Hong Kong, China."— Presentation transcript:

1 July 21, Geoneutrinos Mark Chen Queen’s University OCPA Workshop on Underground Science Hong Kong, China

2 M. Chen OCPA Underground Science 2 July 21, 2008 What are Geoneutrinos? Image by: Colin Rose, Dorling Kindersley radioactive decay of uranium, thorium and from potassium-40 produces antineutrinos assay the entire Earth by looking at its “neutrino glow” e the antineutrinos produced by natural radioactivity in the Earth

3 M. Chen OCPA Underground Science 3 July 21, 2008  note: 40 K also has 10.72% EC branch Q EC =1.505 MeV 10.67% to MeV state (E = 44 keV) 0.05% to g.s. (E = 1.5 MeV) thus also emits e Uranium, Thorium and Potassium from G. Fiorentini % isotopic abundance

4 M. Chen OCPA Underground Science 4 July 21, 2008 How to Detect Geoneutrinos  inverse beta decay: good cross section threshold 1.8 MeV liquid scintillator has a lot of protons and can easily detect sub-MeV events delayed coincidence signal   = 0.2 ms, neutron capture on H  detect delayed 2.2 MeV   rejects backgrounds e + and n correlated in time and in position in the detector threshold figure from KamLAND Nature paper

5 M. Chen OCPA Underground Science 5 July 21, 2008 Expected Geoneutrinos U-Series : 14.9 Th-Series : 4.0 Backgrounds Reactor : 82.3±7.2 (α,n) : 42.4±11.1 Accidental : 2.38±0.01 BG total : 127.4±13.3 Observed : 152 KamLAND First Detection in 2005 reactor neutrinos geo- Number of Geoneutrinos: + 19 - 18 25

6 M. Chen OCPA Underground Science 6 July 21, 2008 Preliminary KamLAND 2008 Geoneutrino Results  factor two more data  13 C( ,n) background error reduced  improved reconstruction (off-axis calibration)  larger fiducial volume  accounting for reactor background time variations  (U+Th geo- ) = (4.4 ± 1.6)  10 6 cm −2 s −1 from S. Enomoto

7 M. Chen OCPA Underground Science 7 July 21, 2008 Geoscience from KamLAND 2008  measured flux consistent with the “Bulk Silicate Earth” model  99%CL upper limit to the geoneutrino flux, fixing the crust contribution, gives heat < 54 TW from S. Enomoto Preliminary

8 M. Chen OCPA Underground Science 8 July 21, 2008 Switch Gears  first part was about neutrino detection  what does this tell us about geoscience? no so much yet…the geoneutrino measurement still has large uncertainties (because of backgrounds) future improvements from KamLAND (e.g. more statistics, reduced errors) will help other experiments: Borexino (taking data), SNO+ (initial construction, partially funded), Hanohano (R&D, proposed)  second part will be about the geoscience that we want to learn from geoneutrinos

9 M. Chen OCPA Underground Science 9 July 21, 2008 Important Questions in Geosciences  what is the planetary K/U ratio? can’t address until we can detect 40 K geoneutrinos  radiogenic contribution to heat flow? geoneutrinos can measure this  radiogenic elements in the core? in particular potassium!  test fundamental models of Earth’s chemical origin  test basic models of the composition of the crust material in subsequent slides from W.F. McDonough

10 July 21, Earth’s Total Surface Heat Flow Conductive heat flow measured from bore-hole temperature gradient and conductivity Total heat flow Conventional view 46  3 TW Challenged recently 31  1 TW Data sources

11 July 21, this is what we think gives rise to the measured heat flow

12 July 21, 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 Urey Ratio and Mantle Convection Models Urey ratio = radioactive heat production heat loss

13 July 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.

14 M. Chen OCPA Underground Science 14 July 21, 2008 Chemical Composition of the Earth  chondrites are primitive meteorites  thought to represent the primordial composition of the solar system  why? relative element abundances in C1 carbonaceous chondrites matches that in the solar photosphere for “refractory elements”  U and Th are refractory elements  K is moderately volatile

15 July 21, Solar photosphere (atoms Si = 1E6) C1 carbonaceous chondrite (atoms Si = 1E6) H C N Li B O

16 M. Chen OCPA Underground Science 16 July 21, 2008 Bulk Silicate Earth  the Earth forms from accreting primordial material in the solar system, an iron metal core separates and compatible metals go into the core  but U, Th (and K?) are lithophile; they prefer to be in the silicate or molten rock around the iron core Earth is basically “rock metal”  can thus estimate the amount of U and Th in the “primitive mantle” using chondrites, the size of the Earth, after core- mantle differentiation → this is the “Bulk Silicate Earth” model  …then, the crust becomes enriched in U, Th and K resulting in a mantle that is depleted (compared to BSE concentrations)

17 July 21, K, Th & U in the Continental Crust Enriched by factor 100 over Primitive Mantle Compositional models for the bulk continental crust Depleted K, Th, U Enriched K, Th, U Cont. Crust ~ 0.6% by mass of silicate earth

18 M. Chen OCPA Underground Science 18 July 21, 2008

19 M. Chen OCPA Underground Science 19 July 21, 2008 Earth Geoneutrino Models  start with the BSE  take reference values for composition of continental and oceanic crust (these come from rock samples)  subtract the crust from the BSE to get the present “residual” mantle  because continental and oceanic are so different, need to use a map of the crust (thickness and crust type) to calculate expected flux at different locations of detectors from C. Rothschild, M. Chen and F. Calaprice 1998

20 M. Chen OCPA Underground Science 20 July 21, 2008 Geoneutrino Flux / Crust Map from Fiorentini, Mantovani, et al. nuclear power reactor background

21 M. Chen OCPA Underground Science 21 July 21, 2008 Getting Back to Geoscience Questions  test fundamental models of Earth’s chemical origin are measured fluxes consistent with predictions based upon the BSE? so far yes, KamLAND 2008 measurement central value equals the BSE predicted flux  test basic ideas of the composition of the crust rock samples used to determine the composition of the crust  depth variations not easily sampled are the basic ideas about the continents and how concentrations are enriched compared to the mantle correct? it suggests measurements at a continental site and one that probes the mantle would be very interesting

22 July 21, 2008 KamLAND: 33 events per year (1000 tons CH 2 ) / 142 events reactor SNO+: 44 events per year (1000 tons CH 2 ) / 38 events reactor Geoneutrinos in SNO+ SNO+ geo-neutrinos and reactor backgroundKamLAND geo-neutrino detection…July 28, 2005 in Nature KamLAND

23 23 July 21, 2008 Geo- from Continental Crust crust: blue mantle: black total: red in SNO+

24 M. Chen OCPA Underground Science 24 July 21, 2008 Good Location for Continental Geo- The Canadian Shield near SNO+ is one of the oldest pieces of continent. Extensive mining activity near Sudbury suggests that the local geology is extremely well studied. W.F. McDonough in Science 317, 1177 (2007) “One proposal is to convert the Sudbury Neutrino Observatory (SNO) to “SNO+” (4). This 1000-ton detector is sited in a mine in Ontario, Canada, and represents an optimal location for measuring the distribution of heat-producing elements in the ancient core of a continent. Here, the antineutrino signal will be dominated by the crustal component at about the 80% level. This experiment will provide data on the bulk composition of the continents and place limits on competing models of the continental crust’s composition.”

25 M. Chen OCPA Underground Science 25 July 21, 2008 Good Location Far from Continents  in the middle of the ocean, near Hawaii, far from continents and also far from nuclear power reactors; depth of 4 km  proposed experiment is Hanohano 10 kton or larger mobile, sinkable retrievable

26 M. Chen OCPA Underground Science 26 July 21, 2008 Hanohano Geoneutrino Sources

27 M. Chen OCPA Underground Science 27 July 21, 2008 Hanohano  moveable geoneutrino detector that probes the chemistry (U, Th) of and the radiogenic heat in the deep Earth  geologists want to know: lateral variability mantle plumes upwelling from the core-mantle boundary mantle convection models  synergy with crust geo- detectors

28 M. Chen OCPA Underground Science 28 July 21, 2008 Concluding Remarks  geoneutrinos prospects transformative science! probe fundamental, big questions in geology  geoneutrino detection, like the Earth itself, is a work in progress!


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