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Low background radioactivity measurements

Low background radioactivity measurements. Pia Loaiza Laboratoire Souterrain de Modane CNRS/CEA, France. Why do we need ultra-low radioactivity measurements? Low background gamma spectrometry: How to achieve high sensitivity ? Material selection in astroparticle experiments

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Low background radioactivity measurements

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  1. Low background radioactivity measurements Pia Loaiza Laboratoire Souterrain de Modane CNRS/CEA, France • Why do we need ultra-low radioactivity measurements? • Low background gamma spectrometry: • How to achieve high sensitivity ? • Material selection in astroparticle experiments • Geochemistry applications • Environmental control • Other applications

  2. n  Shielding close mat. Det. U,Th,K (n,,,) e- Rn Why do we need measurements of ultra-low radioactivity levels ? • Dark matter and 0 experiments : natural radioactivity induces background in rare event searches experiments  need to reduce drastically the radioactive background by material selection Source Reduction • External gamma radiation, • neutrons • Rn and its progenies • Radioimpurities in shielding • materials • Radioimpurities in materials • close to detectors • Contaminants in detector itself Shielding Injection of Radon-reduced air material screening Pia Loaiza ANDES Workshop 11-15 April 2011

  3. How low is ‘low’ ? • ROCK in the Laboratoire Souterrain de Modane: 238U : (10.4  2.5 ) Bq/kg 232Th : (9.96  0.82) Bq/kg • CABLES inEdelweiss II: • 226Ra : (10  7) mBq/kg • 228Th < 6 mBq/kg • COPPER in Edelweiss II: 226Ra : < 40 Bq/kg 228Th : (24 +/- 12) Bq/kg ‘normal’ levels ~10 Bq/kg 1,4 kg of cables ~10 mBq/kg will cause 0.7 neutron/ kg Ge/ year [20-200] keV, (gamma background shielded by Pb)  on the limit of acceptable levels ~10-100 Bq/kg is OK Edelweiss II, NEMO3 materials screened with a sensitivity about 1 mBq/kg (1 Bq= 1 disintegration/s) Pia Loaiza ANDES Workshop 11-15 April 2011

  4. Present and future Gamma background in EDWII: 200 evts/kg Ge/day [20-3000] keV 80 evts/kg Ge/day [20-200] keV EURECA will need Cu with 226Ra, 228Th ~20 Bq/kg to reach dark matter sensitivity goal SuperNEMO needs 0 sources : 208Tl < 2 Bq/kg & 214Bi < 10 Bq/kg Pia Loaiza ANDES Workshop 11-15 April 2011

  5. Mass spectrometry, Neutron Activation Analysis, Alpha-spectrometry ICP-MS ~ 0.01 ppb U/Th (about 0.1 mBq/kg) 238U decay chain HOW TO MEASURE? • Mass spectrometry • Neutron Activation Analysis • Alpha-spectrometry • Gamma spectrometry Sub-chains Pia Loaiza ANDES Workshop 11-15 April 2011

  6. Mass spectrometry, Neutron Activation Analysis, Alpha spectrometry Gamma emitters 232Th decay chain Sub-chains Pia Loaiza ANDES Workshop 11-15 April 2011

  7. Backg. R Detection Limit   . M. I. t Low background Ge detectors for gamma-ray spectrometry • R = resolution • = efficiency I = intensity of the line M = sample mass t = time of measurement To improve sensitivity  BACKGROUND REDUCTION • Cosmic rays reduction: go underground • Environmental gamma reduction: shielding • Intrinsic background reduction: material selection Pia Loaiza ANDES Workshop 11-15 April 2011

  8. 3300 m.w.e + shielding Background sources in Ge gamma-ray spectrometry • Muons on surface GO UNDERGROUND! Background of HPGe spectrometer: 2 106 muons/m2 day on surface 15 m.w.e 15 m.w.e + shielding 26muons/m2 day at 3300 m.w.e (Applied Rad and Isotopes 53 (2000) 191) Pia Loaiza ANDES Workshop 11-15 April 2011

  9. neutron  210Bi (210Pb) DET. - e- 511 keV Pb Rn e- e+ Background sources in Ge gamma spectrometry deep underground Pia Loaiza ANDES Workshop 11-15 April 2011

  10. Ge detector types COAXIAL WELL PLANAR high resolution at low energies high sample mass high efficiency The choice depends on what we want to measure Pia Loaiza ANDES Workshop 11-15 April 2011

  11. Gamma-ray spectrometry at LSM 13 HPGe detectors for: • Material screening for SuperNEMO, Edelweiss and ultra low background instrumentation • (coaxial, planar) • Environmental studies • (well type, planar) • Environmental monitoring • (well type) • Developpement of low background Ge for -spectromety: • Planar, P. Loaiza et al, NIM A 634 (2011) 64–70 • Coaxial (arrived 2011) Pia Loaiza ANDES Workshop 11-15 April 2011

  12. Where do we stand in terms of sensibility? Selected results of radioactivity measurements for material selection: Low energies: 46 keV, 63 keV, 92 keV Higher energies: 200 keV < E < 3000 keV Pia Loaiza ANDES Workshop 11-15 April 2011

  13. Geodynamic studies Studies in lake sediments use radionucleide profiles to date and obtain the sedimentation rates. The requirement on sensitivity is less stringent than those for material selection, but still need low background detectors. 1963 Nuclear weapons tests 1986 Tchernobyl Lac du Bourget Dating using artificial radionucleides 137Cs and 241Am 210Pb excess is used to determine the sedimentation rate ( in this case 3.9 mm/year) Pia Loaiza ANDES Workshop 11-15 April 2011

  14. Geodynamic studies in the southern hemisphere Kastner et al, Global and Planetary Change 72 (2010) 201-214 Lago del Desierto • Lakes Puyehue and Icalma : • F. Arnaud et al, Science of the Total • Environment 366 (2006) 837-850 • Chile and Peru: • Muñoz et al, Deep-Sea Research II 51 • (2004) 2523-2541 Pia Loaiza ANDES Workshop 11-15 April 2011

  15. Environmental monitoring Monitoring of radioactive contamination in the atmosphere Measurements of artificial radionuclides in certain samples require very low backgrounds. 7Be and 137Cs concentration in the atmosphere Pia Loaiza ANDES Workshop 11-15 April 2011

  16. Other applications Bordeaux wine dating The concentration of 137Cs provides a simple method to estimate the wine age. Material selection for integrated circuits Philippe Hubert, Europhysics News (2005) Vol. 36 No. 1 Atmospheric neutrons and on-chip radioactive impurities ( -particle emitters), induce soft-errors in the semiconductors Material selection using high sensitive gamma- spectrometres is being explored G. Warot, P. Loaiza REE 3, Mars 2010, 51 Pia Loaiza ANDES Workshop 11-15 April 2011

  17. SUMMARY • Ultra-low radioactivity measurements are needed for material selection in rare • event searches, like 0 experiments and dark matter • Required levels today ~ 1 - 0.1 mBq/kg • Required levels in future ~ 10 Bq/kg • Method of measurement depends on the radioelement: Mass spectrometry (ICP-MS) for long-lived isotopes, gamma-ray spectrometry for gamma-ray emitters • To improve sensitivity in Ge for -ray spectrometry background must be reduced: • - Cosmic rays reduction: go underground • - Environmental gamma reduction: shielding • - Intrinsic background reduction: material selection • Low-background gamma-ray spectrometry used in several fields: astroparticle physics, geodynamic studies, environmental monitoring, … • Low background Ge for gamma-spectrometry is an ideal tool to be placed in a young underground laboratory: needed for rare-event searches but also may be used for several applications. Low cost. Pia Loaiza ANDES Workshop 11-15 April 2011

  18. Pia Loaiza ANDES Workshop 11-15 April 2011

  19. Costs • Detector with dedicated low-background developpement: • between 100 kEuro and 200 kEuro, depending on crystal mass, • cooling system,… • Shielding: Archeological lead: about 200-250 Euros/kg, Low activity lead: about 2 Euros/kg Lead casting: around 20 kEuros • Commercial acquisition system (hardware + software) : about 10 kEuro Pia Loaiza ANDES Workshop 11-15 April 2011

  20. Which sensitivities for the future experiments? EURECA: • Present  rejection factor ~ 105 • According to simulations: ~105 evts/year in 10 keV<E<50 keV in 1000 kg • of Ge from Cu 226Ra, 228Th : 20 Bq/kg SuperNEMO 40 mBq/kg in 214Bi 3 mBq/kg in 228Th needed for PMTS The necessary sensitivity levels are reached, but time-consuming measurements needed need more detectors further reduce background? Pia Loaiza ANDES Workshop 11-15 April 2011

  21. Performances Planar Resolution: 850 eV at 122 keV Integral count rate 20 keV <E < 1500 keV : 150 cpd All peak-rates < 1 c/day, except 210Pb Pia Loaiza ANDES Workshop 11-15 April 2011

  22. Bruit de fond intégral de quelques détecteurs Ge pour la spectrométrie gamma, divisé par la masse du cristal, en fonction de la profondeur des différents sites souterrains. Le détecteur ‘LSCE’ est de type puits et installé au Laboratoire Souterrain de Modane, ‘JRC-IRMM’ correspond à un détecteur de type coaxial installé au Laboratoire Hades, en Belgique, ‘LNGS’ correspond au taux d’un détecteur coaxial appartenant au groupe du Max Planck Institute de Heidelberg, installé au Gran Sasso. La composante cosmique ne contribue pas au bruit de fond au IRMM : le taux intégral des détecteurs IRMM est comparable à ceux de sites plus profonds Pia Loaiza ANDES Workshop 11-15 April 2011

  23. Radionuclides in the U and Th decay series are useful chronometers for the determination of many processes in the environment. The low natural radioactivity encountered necessitate instrumentation capable of measuring very low radionuclide concentrations. • Some applications : • Quantitative evaluation of both horizontal and vertical mixing rates in the open ocean. • Determination of the rate of particle deposition on the marine sediment layer (originated by both biological and physical processes). • The decay of 210Pb provides a dating method which has been applied to lake sediments. Pia Loaiza ANDES Workshop 11-15 April 2011

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