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The role of Po-210 and Pb-210 in Low Radioactivity Experiments and Ultrapure Water. Marco G. Giammarchi Istituto Nazionale di Fisica Nucleare Via Celoria 16 – 20133 Milano (Italy) marco.giammarchi@mi.infn.it http://pcgiammarchi.mi.infn.it/giammarchi/. Po and Pb Radioisotopes
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The role of Po-210 and Pb-210 in Low Radioactivity Experiments and Ultrapure Water Marco G. Giammarchi Istituto Nazionale di Fisica Nucleare Via Celoria 16 – 20133 Milano (Italy) marco.giammarchi@mi.infn.it http://pcgiammarchi.mi.infn.it/giammarchi/ • Po and Pb Radioisotopes • LowRadioactivityExperiments • Role of Po and Pb Isotopes • Ultrapure Water INCO-PoPb-2013 - Mangalore, February 2013
Po and Pb RadioIsotopes They are located at the end of U,Th radioactive chains Thorium Uranium INCO-PoPb-2013 - Mangalore, February 2013
The Actinium and Neptuniumseries (a lessimportantrole in experiments) Neptunium Uranium 235 INCO-PoPb-2013 - Mangalore, February 2013
A sort of summary of abundant isotopes (incomplete) INCO-PoPb-2013 - Mangalore, February 2013
Low Radioactivity Experiments Astrophysics & Cosmology Astroparticle Physics Particle & Nuclear Physics Research topics: • Solar Neutrinos • Double Beta Decay • Proton Stability • Geoneutrinos • Supernovae detection • …. Impact on fundamental physics (Weak Interactions, Neutrino Oscillation, Standard Model) Physics experiments in which the signal searched for in swamped in a very high (dominant) background INCO-PoPb-2013 - Mangalore, February 2013
Laboratori Nazionali del Gran Sasso 1700 m of rock to shield against cosmic rays 3 Experimental Halls, each the size of a football field INCO-PoPb-2013 - Mangalore, February 2013
BorexinoDetector Scintillator: 270 t PC+PPO (1.5 g/l) in a 150 m thick innernylon vessel (R = 4.25 m) Stainless Steel Sphere: R = 6.75 m 2212 PMTs 1350 m3 Buffer region: PC+DMPquencher (5 g/l) 4.25 m < R < 6.75 m Water Tank: and n shield water Č detector 208 PMTs in water 2100 m3 Outer nylon vessel: R = 5.50 m (222Rn barrier) Carbon steel plates 20 steel legs INCO-PoPb-2013 - Mangalore, February 2013
The Borexino Detector for Solar Neutrino Physics at Gran Sasso Eν = 862 keV (monoenergetic) ΦSSM = 4.8· 109 ν s-1 cm2 Electron recoil spectrum Cross Section 10-44 cm2 (@ 1MeV) INCO-PoPb-2013 - Mangalore, February 2013 8
A tribute to the main author of the Borexino Proposal INCO-PoPb-2013 - Mangalore, February 2013
What is the matter with a Low Background Experiment? • SIGNAL • 50 events/day in 300 tonnes of liquid scintillator in Borexino (Be-7 signal) • BACKGROUNDS • Cosmic Rays (even undeground!) will need to be reduced by a factor ≈ 103 • Radioactivity of Materials. For U,Th, K normal concentrations, say as an example, 10-11 g/g of 238U Signal to Noise ratio can be as low aso 50 / 3x106 !! INCO-PoPb-2013 - Mangalore, February 2013
Role of Po and Pb Isotopes In the U-238 chain Po-218: 6.0 MeV, T(1/2)=3.10 min, αdecay. The best Rn-222 tracer (after Rn-222 itself) Po-214: 7.7 MeVαdecay. With a half-life of 1.64x10-4 s, itis the basis of the famous Bi-Po tagging (delayedcoincidence of 214 isotopes) Po-210: 5.3 MeVαdecay out of equilibrium with the rest of the chain. Half-life of 138.4 days (can move in materials) Pb-214: A Rndaughter with a 1.024 MeV, 26.8 minbeta+gamma to Bi-214. Pb-210: 0.22 MeVβ+γ 22.3 yrslifetime. Build-up isotope! Pb-206: stable. Will end the U-238 chain. INCO-PoPb-2013 - Mangalore, February 2013
In the Th-232 chain Po-216: 6.8 MeV, T(1/2)=0.15 s, αdecay. The best Rn-220 (Thoron) tracer Po-212: 1.12 MeVαdecay. With a half-life of 3x10-7 s, itis the basis of the famous Bi-Po tagging (delayedcoincidence of 212 isotopes) Pb-212: A Rndaughter with a T(1/2)=10.6 hrminbeta+gammadecay to Bi-212. Pb-208: stable. Will end the Th-232 chain. What does it mean in a large scale Low Background Experiment? INCO-PoPb-2013 - Mangalore, February 2013
Borexino single photoelectron spectrum to search for Solar Neutrinos Po-210 alphadecay Not in equilibrium with Rn-222 Concentration of Po-210 in our scintillator before the analysis cuts INCO-PoPb-2013 - Mangalore, February 2013
Pb-210 and Bi-210 background Bi-210 decays Concentration of Pb-210 in our scintillator E cannot measure by analytic methods. We can measure by counting. But in doing this we face all radioactivity components INCO-PoPb-2013 - Mangalore, February 2013
Single volume liquid scintillator detectors SNO+ KamLAND Borexino 300t Running since 2007. 1000t Starting in 2012 1000t Running since 2002. MiniBOONE 700t Running since 2004. INCO-PoPb-2013 - Mangalore, February 2013
Ultrapure Water • Widelyused in LowRadioactivityExperiments: • Cheap • Widelyavailable • Flexibleshielding • Can be purified • Can be used for cleaning Purification processes to reach the lowest level of contamination possible INCO-PoPb-2013 - Mangalore, February 2013
Borexino Main Water Purification Plant Filtering Reverse Osmosis Ion removal Degassing Ultra-Q F153 0.1 μm Pre F140 1000 l/h RO2 EDI Stripping White Tank F141 1500 l/h 3000 l/h F156 0.02 μm G159 RO1 Degassifier Liqui-Cel POU G154
Summary of the Water Purification System performance (Bq/kg) Unfortunately, no real clue on Pb or Po isotopes Pb-208 measured as a tracer with hi-res mass spectrometry INCO-PoPb-2013 - Mangalore, February 2013
Conclusions • Po, Pb (Bi) radiosotopes are important as a limiting background to Low Radioactivity Experiments • We do not understand Po,Pb radioisotopes in (e.g.) scintillators • Limited information on Po,Pb radioisotopes in (e.g.) scintillators • We know nothing about Po,Pb leftover in Ultrapure Water INCO-PoPb-2013 - Mangalore, February 2013
Thankyou for yourattention INCO-PoPb-2013 - Mangalore, February 2013
Discrimination between alpha and beta decays in scintillators (PSD) A technique to discard alpha decays in the scintillator and extract the signal Discrimination between alphas and beta decays: INCO-PoPb-2013 - Mangalore, February 2013