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ISAPP 2004 International School on AstroParticle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004Lino Miramonti 1 ISAPP 2004 International.

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Presentation on theme: "ISAPP 2004 International School on AstroParticle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004Lino Miramonti 1 ISAPP 2004 International."— Presentation transcript:

1 ISAPP 2004 International School on AstroParticle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004Lino Miramonti 1 ISAPP 2004 International School on AstroParticle Physics LNGS Italy – June 28 th – July 9 th 2004

2 ISAPP 2004 International School on AstroParticle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004Lino Miramonti 2 Earth emits a tiny heat flux with an average value of Φ H ~ mW/m 2 Integrating over the Earth surface: H E ~ TW Giving constrain on the heat generation within the Earth. Detecting antineutrino emitted by the decay of radioactive isotopes It is possible to study the radiochemical composition of the Earth

3 ISAPP 2004 International School on AstroParticle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004Lino Miramonti 3 (ε is the present natural isotopic abundance) 238 U 232 Th 40 K The 235 U chain contribution can be neglected

4 ISAPP 2004 International School on AstroParticle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004Lino Miramonti 4 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 The best method to detect electron antineutrino is the classic Cowan Reines reaction of capture by proton in a liquid scintillator:

5 ISAPP 2004 International School on AstroParticle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004Lino Miramonti U and 232 Th chains have 4 β with E > 1.8 MeV : end.point [Th-chain] 228 Ac< 2.08 MeV [Th-chain] 212 Bi< 2.25 MeV [U-chain] 234 Pa< 2.29 MeV [U-chain] 214 Bi< 3.27 MeV Anti-neutrino from 40 K 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

6 ISAPP 2004 International School on AstroParticle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004Lino Miramonti 6 Threshold: 250 keV (due to 14 C) Energy Resolution: FWHM 1 MeV Spatial Resolution: 10 1 MeV PC + PPO (1,5 g/l) = 0.88 g cm -3 n = Borexino is an unsegmented detector featuring 300 tons of ultra-pure liquid scintillator (C 9 H 12 ) viewed by 2200 PMTs The most problematic background for this reaction is due to fast neutrons (especially those produced by muon interactions) At LNGS µ reducing factor ~ 10 6 ( ~1 µ m -2 h -1 ) Borexino µ veto ~ 1/5000 ( ~0.07 µ m -2 y -1 ) ΔM is the neutron-proton mass difference and f n values come from n β decay

7 ISAPP 2004 International School on AstroParticle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004Lino Miramonti 7 Geo-neutrinos can probe the Earths 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 (Earths radioactivity) To test the origins of the Earth: The Bulk Silicate Earth

8 ISAPP 2004 International School on AstroParticle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004Lino Miramonti 8 Equation for Heat (H) and Neutrinos Luminosity (L)

9 ISAPP 2004 International School on AstroParticle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004Lino Miramonti 9 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). 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. BSE concentrations of: have been suggested M Mantle = 68% M Earth M(U) = 20 ppb · 0.68 · 6·10 27 g = 8.5·10 19 g Primitive Mantle

10 ISAPP 2004 International School on AstroParticle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004Lino Miramonti 10 During the formation of the Earths crust the primitive mantle was depleted (in U, Th and K) while the crust was enriched. Samples measurements of the crust provide isotopic abundance information: 238 U 232 Th Primitive Mantle (BSE)20 ppb(20 ppb)·3.8 Continental Crust910 ppb3500 ppb Oceanic Crust100 ppb360 ppb Present depleted Mantle15 ppb60 ppb 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: Global Crustal Model A Global Crustal Model at 2° x 2° (http://quake.wr.usgs.gov/study/CrustalStructure/) Continental Crust: average thickness ~ 40 km Oceanic Crust: average thickness ~ 6 km CC is about 10 times richer in U and Th than OC

11 ISAPP 2004 International School on AstroParticle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004Lino Miramonti 11 Borexino is located in the Gran Sasso underground laboratory (LNGS) in the center of Italy: 42°N 14°E Calculated anti-ν e flux at the Gran Sasso Laboratory (10 6 cm -2 s -1 ) UThTotal (U+Th)Reactor BKG CrustMantleCrustMantle Data from the International Nuclear Safety Center (http://www.insc.anl.gov)

12 ISAPP 2004 International School on AstroParticle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004Lino Miramonti 12 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)


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