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Geoneutrinos detection in Borexino

Geoneutrinos detection in Borexino. ISAPP 2004 International School on AstroParticle Physics LNGS Italy – June 28 th – July 9 th 2004. Lino Miramonti. Earth emits a tiny heat flux with an average value of Φ H ~ 60-80 mW/m 2 Integrating over the Earth surface: H E ~ 30-40 TW.

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Geoneutrinos detection in Borexino

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  1. Geoneutrinos detection in Borexino ISAPP 2004 International School on AstroParticle Physics LNGS Italy – June 28th – July 9th 2004 Lino Miramonti Lino Miramonti

  2. Earth emits a tiny heat flux with an average value of ΦH~ 60-80 mW/m2 Integrating over the Earth surface: HE ~ 30-40 TW Detecting antineutrino emitted by the decay of radioactive isotopes It is possible to study the radiochemical composition of the Earth Giving constrain on the heat generation within the Earth. Lino Miramonti

  3. 238U 232Th 40K Radioelements The 235U chain contribution can be neglected (ε is the present natural isotopic abundance) Lino Miramonti

  4. Principle of anti-neutrino detection The best method to detect electron antineutrino is the classic Cowan Reines reaction of capture by proton in a liquid scintillator: The electron antineutrino tag is made possible by a delayed coincidence of the e+ and by a 2.2 MeV γ-ray emitted by capture of the neutron on a proton after a delay of ~ 200 µs Threshold Lino Miramonti

  5. 238U and 232Th chains have 4 βwith E > 1.8 MeV : Anti-neutrino from 40K are under threshold! The terrestrial antineutrino spectrum above 1.8 MeV has a “2-component” shape. high energy component coming solely from U chain and low energy component coming with contributions from U + Th chains This signature allows individual assay of U and Th abundance in the Earth Lino Miramonti

  6. Borexino is an unsegmented detector featuring 300 tons of ultra-pure liquid scintillator (C9H12) viewed by 2200 PMTs ΔM is the neutron-proton mass difference and fn values come from n β decay PC + PPO (1,5 g/l) r = 0.88 g cm-3 n = 1.505 background The most problematic background for this reaction is due to fast neutrons (especially those produced by muon interactions) At LNGS µ reducing factor ~ 106 ( ~1 µ m-2 h-1) Borexino µ veto ~ 1/5000 ( ~0.07 µ m-2 y-1) Threshold: 250 keV (due to 14C) Energy Resolution: FWHM  12% @ 1 MeV Spatial Resolution:  10 cm @ 1 MeV Lino Miramonti

  7. Geo-neutrinos can probe the Earth’s interior Geochemical analysis Only the crust and the very upper mantle are directly accessible to geochemical analysis Seismology By seismology analysis is possible to reconstruct the density profile but not the chemical composition of the earth. Geoneutrinos Geoneutrinos can provide the chemical composition (in terms of U, Th and K) of the Earth interior • Thank to Geoneutrinos it will be possible: • To measure the long lived radioisotopes inside the Earth (Earth’s radioactivity) • To test the origins of the Earth: The Bulk Silicate Earth Lino Miramonti

  8. Equation for Heat (H) and Neutrinos Luminosity (L) H L Lino Miramonti

  9. Primitive Mantle The starting point for determining the distribution of U, Th and K in the present CRUST and MANTLE is understanding the composition of the “Bulk Silicate Earth” (BSE), which is the model representing the primordial mantle prior to crust formation consistent with observation and geochemistry (equivalent in composition to the modern mantle plus crust). BSE concentrations of: have been suggested H M Mantle= 68% M Earth M(U) = 20 ppb · 0.68 · 6·1027g = 8.5·1019g • In the BSE model: • The radiogenic heat production H rate is ~ 20 TW • (~ 8 TW from U, ~ 8.6 TW from Th, ~ 3 TW from K) • The antineutrino production L is dominated by K. L Lino Miramonti

  10. During the formation of the Earth’s crust the primitive mantle was depleted (in U, Th and K) while the crust was enriched. Continental Crust: average thickness ~ 40 km Oceanic Crust: average thickness ~ 6 km CC is about 10 times richer in U and Th than OC Samples measurements of the crust provide isotopic abundance information: It is possible to deduce the average U and Th concentrations in the present depleted mantle. Crust type and thickness data in the form of a global crust map: A Global Crustal Model at 2° x 2° (http://quake.wr.usgs.gov/study/CrustalStructure/) Lino Miramonti

  11. Borexino is located in the Gran Sasso underground laboratory (LNGS) in the center of Italy: 42°N 14°E Data from the International Nuclear Safety Center(http://www.insc.anl.gov) Lino Miramonti

  12. Positron energy spectrum from antineutrino events in Borexino The number expected events in Borexino are: The background will be: The reactor anti-neutrino background has a well-known shape: it can be easily subtracted allowing (~8 of them in the same spectral region as the terrestrial anti-ν) U+Th European Reactors Lino Miramonti

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