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

Pia Loaiza ANDES Workshop April  U,Th,K (n, , ,  ) Shielding close mat. e-e- n Det. Rn External gamma radiation, neutrons Rn and its progenies Radioimpurities in shielding materials Radioimpurities in materials close to detectors Contaminants in detector itself material screening Source Reduction Shielding Injection of Radon-reduced air 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

Pia Loaiza ANDES Workshop April ,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 Edelweiss II, NEMO3 materials screened with a sensitivity about 1 mBq/kg ‘normal’ levels ~10 Bq/kg How low is ‘low’ ?  ROCK in the Laboratoire Souterrain de Modane: 238 U : (10.4  2.5 ) Bq/kg 232 Th : (9.96  0.82) Bq/kg  CABLES in Edelweiss II: 226 Ra : (10  7) mBq/kg 228 Th < 6 mBq/kg  COPPER in Edelweiss II: 226 Ra : < 40  Bq/kg 228 Th : (24 +/- 12)  Bq/kg ~  Bq/kg is OK (1 Bq= 1 disintegration/s)

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

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

Pia Loaiza ANDES Workshop April Th decay chain Gamma emitters Sub-chains Mass spectrometry, Neutron Activation Analysis, Alpha spectrometry

Pia Loaiza ANDES Workshop April Low background Ge detectors for gamma-ray spectrometry  Backg. R . M. I.  t Detection Limit  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 April Background sources in Ge gamma-ray spectrometry Muons on surface GO UNDERGROUND! (Applied Rad and Isotopes 53 (2000) 191) Background of HPGe spectrometer: 3300 m.w.e + shielding 15 m.w.e + shielding muons/m 2 day on surface 26 muons/m 2 day at 3300 m.w.e 15 m.w.e

Pia Loaiza ANDES Workshop April DET.  e-e- neutron 210 Bi ( 210 Pb) -- 511 keV Rn e-e- e+e+ Pb Background sources in Ge gamma spectrometry deep underground SOURCEREDUCTION  External gamma radiation (up to 2.6 MeV 208 Tl)Shielding  Radioimpurities in cryostatMaterial selection  Rn and its progeniesRn reduced air  Radioimpurities in the shielding materialsMaterial selection

Pia Loaiza ANDES Workshop April Ge detector types COAXIALWELLPLANAR high sample mass high efficiency high resolution at low energies The choice depends on what we want to measure

Pia Loaiza ANDES Workshop April 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 April Selected results of radioactivity measurements for material selection: Where do we stand in terms of sensibility? MaterialDetectorMass (g) Time (h) 210 Pb (mBq/kg) 234 Th( 238 U ) (mBq/kg) 226 Ra (mBq/kg) 228 Ra (mBq/kg) 228 Th (mBq/kg) AluminiumMafalda (Planar) < 9<3<0.9<1 1.0  0.3 EpoxyMafalda (Planar)  714  39292 < 6 10  3 GlueIris (Coaxial) < 0.135< 0.274< CopperGeMPI2 (coaxial) <0.04<  0.01 Low energies: 46 keV, 63 keV, 92 keV Higher energies: 200 keV < E < 3000 keV

Pia Loaiza ANDES Workshop April 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. Geodynamic studies Lac du Bourget Dating using artificial radionucleides 137 Cs and 241 Am 1986 Tchernobyl 1963 Nuclear weapons tests 210 Pb excess is used to determine the sedimentation rate ( in this case 3.9 mm/year)

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

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

Pia Loaiza ANDES Workshop April Bordeaux wine dating The concentration of 137 Cs provides a simple method to estimate the wine age. Material selection for integrated circuits Other applications 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 Philippe Hubert, Europhysics News (2005) Vol. 36 No. 1

Pia Loaiza ANDES Workshop April SUMMARY  Ultra-low radioactivity measurements are needed for material selection in rare event searches, like 0  experiments and dark matter Required levels today ~ 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 April

Pia Loaiza ANDES Workshop April Costs  Detector with dedicated low-background developpement: between 100 kEuro and 200 kEuro, depending on crystal mass, cooling system,…  Shielding: Archeological lead: about 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 April Which sensitivities for the future experiments? EURECA: Present  rejection factor ~ 10 5 According to simulations: ~10 5 evts/year in 10 keV<E<50 keV in 1000 kg of Ge from Cu 226Ra, 228Th : 20  Bq/kg The necessary sensitivity levels are reached, but time-consuming measurements needed need more detectors SuperNEMO 40 mBq/kg in 214Bi 3 mBq/kg in 228Th needed for PMTS further reduce background?

Pia Loaiza ANDES Workshop April 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 210 Pb

Pia Loaiza ANDES Workshop April 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 April 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 210 Pb provides a dating method which has been applied to lake sediments.