ISAPP 2004 International School on Astro Particle Physics

Earth emits a tiny heat flux with an average value of ΦH ~ 60

238 U 232 Th 40 K The 235 U chain contribution can be neglected

The best method to detect electron antineutrino is the classic Cowan Reines reaction of

238 U and 232 Th chains have 4 β with E > 1. 8

Borexino is an unsegmented detector featuring 300 tons of ultra-pure liquid scintillator (C 9

Geo-neutrinos can probe the Earth’s interior Geochemical analysis Only the crust and the very

Equation for Heat (H) and Neutrinos Luminosity (L) ISAPP 2004 International School on Astro.

Primitive Mantle The starting point for determining the distribution of U, Th and K

During the formation of the Earth’s crust the primitive mantle was depleted (in U,

Borexino is located in the Gran Sasso underground laboratory (LNGS) in the center of

The number expected events in Borexino are: The background will be: The reactor anti-neutrino

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

Earth emits a tiny heat flux with an average value of ΦH ~ 60 -80 m. W/m 2 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. ISAPP 2004 International School on Astro. Particle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004 Lino Miramonti 2

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

The best method to detect electron antineutrino is the classic Cowan Reines reaction of capture by proton in a liquid scintillator: Threshold ISAPP 2004 International School on Astro. Particle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004 The electron antineutrino tag is made possible by a delayed coincidence of the e+ and by a 2. 2 Me. V γ-ray emitted by capture of the neutron on a proton after a delay of ~ 200 µs Lino Miramonti 4

238 U and 232 Th chains have 4 β with E > 1. 8 Me. V : Anti-neutrino from 40 K end. point [Th-chain] 228 Ac < 2. 08 Me. V [Th-chain] 212 Bi < 2. 25 Me. V [U-chain] 234 Pa < 2. 29 Me. V [U-chain] 214 Bi < 3. 27 Me. V are under threshold! The terrestrial antineutrino spectrum above 1. 8 Me. V 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 ISAPP 2004 International School on Astro. Particle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004 Lino Miramonti 5

Borexino is an unsegmented detector featuring 300 tons of ultra-pure liquid scintillator (C 9 H 12) viewed by 2200 PMTs PC + PPO (1, 5 g/l) r = 0. 88 g cm-3 n = 1. 505 ΔM is the neutron-proton mass difference and f n values come from n β decay 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 ke. V (due to 14 C) Energy Resolution: FWHM 12% @ 1 Me. V Spatial Resolution: 10 cm @ 1 Me. V ISAPP 2004 International School on Astro. Particle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004 Lino Miramonti 6

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 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 ISAPP 2004 International School on Astro. Particle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004 Lino Miramonti 7

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

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 M Mantle= 68% M Earth M(U) = 20 ppb · 0. 68 · 6· 1027 g = 8. 5· 1019 g 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. ISAPP 2004 International School on Astro. Particle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004 Lino Miramonti 9

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: 238 U Primitive Mantle (BSE) It is possible to deduce the average U and Th concentrations in the present depleted mantle. 232 Th 20 ppb (20 ppb)· 3. 8 Continental Crust 910 ppb 3500 ppb Oceanic Crust 100 ppb 360 ppb 15 ppb 60 ppb 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/Crustal. Structure/) ISAPP 2004 International School on Astro. Particle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004 Lino Miramonti 10

Borexino is located in the Gran Sasso underground laboratory (LNGS) in the center of Italy: 42°N 14°E Calculated anti-νe flux at the Gran Sasso Laboratory (106 cm-2 s-1) U Crust Th Mantle 1. 8 1. 4 Crust Total (U+Th) Reactor BKG 5. 9 0. 65 Mantle 1. 5 1. 2 ISAPP 2004 International School on Astro. Particle Physics - Laboratori Nazionali del Gran Sasso - 28 June 9 July 2004 Data from the International Nuclear Safety Center (http: //www. insc. anl. gov) Lino Miramonti 11

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