Low background radioactivity measurements Pia Loaiza Laboratoire Souterrain

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 11 -15 April 2011

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 n Source Shielding close mat. Det. e- Rn U, Th, K (n, , , ) • External gamma radiation, neutrons Reduction Shielding Injection of • Rn and its progenies Radon-reduced air • Radioimpurities in shielding materials • Radioimpurities in materials close to detectors material screening • Contaminants in detector itself Pia Loaiza ANDES Workshop 11 -15 April 2011 2

How low is ‘low’ ? q ROCK in the Laboratoire Souterrain de Modane: 238 U : (10. 4 2. 5 ) Bq/kg 232 Th : (9. 96 0. 82) Bq/kg q CABLES in Edelweiss II: 226 Ra : (10 7) m. Bq/kg 228 Th < 6 m. Bq/kg q COPPER in Edelweiss II: 226 Ra : < 40 Bq/kg 228 Th : (24 +/- 12) Bq/kg ‘normal’ levels ~10 Bq/kg 1, 4 kg of cables ~10 m. Bq/kg will cause 0. 7 neutron/ kg Ge/ year [20 -200] ke. V, (gamma background shielded by Pb) on the limit of acceptable levels ~10 -100 Bq/kg is OK Edelweiss II, NEMO 3 materials screened with a sensitivity about 1 m. Bq/kg (1 Bq= 1 disintegration/s) Pia Loaiza ANDES Workshop 11 -15 April 2011 3

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

Mass spectrometry, Neutron Activation Analysis, Alpha-spectrometry ICP-MS ~ 0. 01 ppb U/Th (about 0. 1 m. Bq/kg) 238 U decay chain HOW TO MEASURE? • Mass spectrometry • Neutron Activation Analysis • Alpha-spectrometry • Gamma spectrometry Sub-chains Pia Loaiza ANDES Workshop 11 -15 April 2011 5

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

Low background Ge detectors for gamma-ray spectrometry Detection Limit Backg. R . M. I. t 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 7

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

Background sources in Ge gamma spectrometry deep underground SOURCE REDUCTION q External gamma radiation (up to 2. 6 Me. V 208 Tl) Shielding q Radioimpurities in cryostat Material selection neutron q Rn and its progenies Rn reduced air q Radioimpurities in the shielding materials Material selection DET. - 210 Bi (210 Pb) e 511 ke. V Rn Pb e+ e. Pia Loaiza ANDES Workshop 11 -15 April 2011 9

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

Gamma-ray spectrometry at LSM 13 HPGe detectors for: • Material screening for Super. NEMO, 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 11

Where do we stand in terms of sensibility? Selected results of radioactivity measurements for material selection: Material Detector Mass (g) Time (h) 210 Pb 234 Th(238 U) 226 Ra 228 Th (m. Bq/kg) Aluminium Mafalda (Planar) 1025 132 <9 <3 <0. 9 <1 1. 0 0. 3 Epoxy Mafalda (Planar) 47 384 35 7 14 3 9 2 <6 10 3 Glue Iris (Coaxial) 2500 768 < 0. 135 < 0. 274 < 0. 174 Copper Ge. MPI 2 (coaxial) 42500 564 <0. 06 0. 02 0. 01 Low energies: 46 ke. V, 63 ke. V, 92 ke. V Higher energies: 200 ke. V < E < 3000 ke. V Pia Loaiza ANDES Workshop 11 -15 April 2011 12

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 1986 Lac du Bourget Tchernobyl Nuclear weapons tests Dating using artificial radionucleides 137 Cs and 241 Am 210 Pb excess is used to determine the sedimentation rate ( in this case 3. 9 mm/year) Pia Loaiza ANDES Workshop 11 -15 April 2011 13

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 14

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

Other applications Material selection for integrated circuits Bordeaux wine dating The concentration of 137 Cs provides a simple method to estimate the wine age. 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 gammaspectrometres is being explored G. Warot, P. Loaiza REE 3, Mars 2010, 51 Pia Loaiza ANDES Workshop 11 -15 April 2011 16

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 m. Bq/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 17

Pia Loaiza ANDES Workshop 11 -15 April 2011 18

Costs § Detector with dedicated low-background developpement: between 100 k. Euro and 200 k. Euro, 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 k. Euros § Commercial acquisition system (hardware + software) : about 10 k. Euro Pia Loaiza ANDES Workshop 11 -15 April 2011 19

Which sensitivities for the future experiments? EURECA: • Present rejection factor ~ 105 • According to simulations: ~105 evts/year in 10 ke. V<E<50 ke. V in 1000 kg of Ge from Cu 226 Ra, 228 Th : 20 Bq/kg Super. NEMO 40 m. Bq/kg in 214 Bi 3 m. Bq/kg in 228 Th 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 20

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

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 Pia Loaiza ANDES Workshop 11 -15 April 2011 22 des détecteurs IRMM est comparable à ceux de sites plus profonds

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. Pia Loaiza ANDES Workshop 11 -15 April 2011 23