Pia Loaiza AARM March 2010 Background studies for EURECA EURECA The ‘submarine’ (water tank) design: background expected from stainless steel structure The ‘pool’ design: - gamma background from vessel - gamma background from copper - beta background and rejection
Pia Loaiza AARM March pb goal = no background in kg.d Joint effort from teams from EDELWEISS, CRESST, ROSEBUD, CERN, + others… >>100 kg cryogenic experiment, multi- target Part of ILIAS/ASPERA European Roadmap Preferred site: m 3 extension of present LSM (4 /m2/d), to be dug in EURECA
Pia Loaiza AARM March events -equivalent to ~10 3 kgd arXiv: accepted by PLB Gamma Rejection better than 1 in 10 5 EDELWEISS II: GAMMA REJECTION
Pia Loaiza AARM March 2010 HALL B: DARK MATTER (EURECA TYPE) Hall B m 3 Approx. dimensions: 18x15x50 m Internal dimensions (2400 m 3 ): 11x6x46 m water First shielding configuration: the ‘submarine’ design
Pia Loaiza AARM March 2010 STAINLESS STEEL 226 Ra 228 Th 40 K 60 CoSUM Borexino Steel for flanches Astrop. Phys. 18, 1 (2002) A (mBq/kg) 6.2 1.6 < 1 Single e - recoils < Double Chooz Outkumpu P. Loaiza A (mBq/kg) 5 25.5 1.3 < 2 Single e - recoils < Edelweiss 304L C. Goldbach, G. Nollez A (mBq/kg) 4 25 214 1014 3 Single e - recoils GERDA Ugine&Alz Ti W. Maneschg et al NIM A 593, 448 (2008) A (mBq/kg) < 0.74< 0.41< 0.7 Single e - recoils < 32000<19100< XENON Fábrica del Campo de Gibraltar, Cádiz 316Ti From L. Baudis, IDM08 A (mBq/kg) < 1.3< 0.9< Single e - recoils 57000<42000< Events from 2cm thick water-tank per 100 kg Ge per year, 10 keV <E r < 50 keV ~2 ·10 5 Simulations by V. Kudryavtsev et al
Pia Loaiza AARM March 2010 Gamma background from stainless steel water tank for the ‘submarine’ configuration pb goal = no background in kg.d from stainless steel water-tank: 2 ·10 5 evts/100 kg year = 8 ·10 5 evts in kg.d Gamma rejection factor in EDWII : 1 in 10 5 Untolerable gamma background
Pia Loaiza AARM March 2010 ‘Pool’ configuration Preliminary layout, to be evolved By CEA/IRFU
Pia Loaiza AARM March 2010 cryostat Cold Signals in/out Amplis Pure water Radiation level -gamma -neutron neutron gamma
Pia Loaiza AARM March 2010 Attenuation of gamma-rays by water Swimming-pool: without water, comparable e recoil event rate expected wrt ‘submarine’ design Around factor attenuation if 3 m water-shield Different attenuation factors for different energies, hence for K, Co, U series → we expect no gamma-background events in the detectors from water tank vessel in the ‘pool’ design Plot by V. Kudryavtsev et al
Pia Loaiza AARM March U 232 Th 40 K 60 Co A (ppb) mBq/kg Single e - recoils/year 1.9 · ·10 5 Gamma background expected from Cu Simulations by V. Kudryavtsev et al Simulation results for e - recoils expected in 500 kg of Ge from copper parts (cryostat=2173 kg + inner parts = 692 kg), keV: Copper 226 Ra 228 Th 40 K 60 CoSUM NOSV G. Heusser, LRT2004 A ( Bq/kg) < 20< 23< 90< 10 Single e - recoils/year ~ 2 ·10 4 ~ 4 ·10 3 ~ 2 ·10 4 Which translates to: → roughly, we need the previous Cu purity to get acceptable backg levels
Pia Loaiza AARM March 2010 Beta background and rejection arXiv: v1 EDELWEISS II: beta calibration with a 210 Pb source: Beta backgroundLevel of 210 Pb backg in ROIID rejection factor Residual background Edelweiss (fid. volume Ge)3 evts/kg.d 1 / 10 5 1 / kg.d EURECA Ge0.3 evts/kg.d 1 / 10 5 1 / kg.d
Pia Loaiza AARM March 2010 SUMMARY We have considered the water-tank design: Unacceptable gamma background from the stainless steel structure Hence, we’ve chosen the ‘pool’ design: - no gammas expected in detectors from the vessel - need cryostat copper with 20 Bq/kg to get reasonable background levels - beta background should not be a problem if the level of surface contamination is improved by a factor 10 – within reach
Pia Loaiza AARM March 2010 Measurements of extremely low radioactivity levels in stainless steel for GERDA Amount of costly copper to be used depends drastically on the contamination of stainless steel NIM A Vol. 593, 448 (2008), W. Maneschg et al W. Manesch, H. Simgen: Private comm. Commonly available stainless steel : Ti has very low concentrations in primordial radionuclides (Mo content allows high corrosion resistance) Measurement campaign in collaboration with trading company Nironit Samples from different European manufacturers ElementCSiMnPSCrMoNiTi Min (%) (5xC) Max (%) 0.08 1.00 2.00
Pia Loaiza AARM March 2010 SampleG2G3G5G6 VendorIlsenburgUgine&AlzAcroniIlsenburg 228 Ra (mB/kg)< 0.86< 0.5 < Th (mB/kg)<0.11< 0.2 < Ra (mB/kg)<0.24< 0.6 < m Pa (mB/kg)<12< 16 < U (mB/kg)<0.63< 1.5 < K (mB/kg)<0.93< 1.1< 0.81< Co (mB/kg) 14.0 Cs (mB/kg)<0.16<0.36< 0.1< Be (mB/kg)<3< Mn (mB/kg) 1.5 Co (mB/kg) 0.99 Co (mB/kg) 0.17 0.06 < 0.10 < Sc (mB/kg) 0.24 0.06 < 0.14 < V (mB/kg) 0.36 0.12 U < 1 mBq/kg, Th < 1 mBq/kg, 40 K < 1 mBq/kg, 60 Co ~ 10 mBq/kg
Pia Loaiza AARM March 2010 For easier comparison activities are given as U, Th and K concentrations. For the conversion of 226Ra into U and 228Th into Th secular equilibrium was assumed although this is seldom the case Concentrations in SS used in previous experiments Collab.Ref. / measureDescription 238 U (ppb) mBq/kg 232 Th (ppb) mBq/kg nat K (ppm) mBq/kg 60 Co (mBq/kg) BOREXINOAst.Phys. 18, 1, 2002 AISI304L for SSS 0.37 1.1 < 0.45 < 14 6161 Steel for flanges 0.5 1.6 < 0.42 <13 14 1 Steel for storage vessel 1.4 2.6 <0.6 <19 12 2 Steel TK3B for storage vessel 0.4 2 46 3 DOUBLE CHOOZ P. LoaizaOutokumpu 0.41 1.3 <0.47 <15 14 2 EDWC. Goldbag and G. Nollez 304L 0.32 3
Pia Loaiza AARM March 2010
‘Xenon stainless steel’ 316Ti steel Provider: Nironit Edelstahlhandel GmbH & Co. KG Producer: Fábrica del Campo de Gibraltar, Cádiz Grade of the material : X6CrNiMoTi Works Grade : ACX Need to scan the samples since the 60 Co content may vary with charge number
Pia Loaiza AARM March 2010 NEMO 3/SUPERNEMO PURE IRON Iron petals for NEMO 3 Will be used also for SuperNemo AK Steel, provider in France, had already get to an ‘understanding’ concerning the screening of the samples prior to the ‘command’ with LAL: Open to their needs. Material 214 Bi ( 226 Ra) (mBq/kg) 208 Tl ( 228 Th) (mBq/kg) 40 K (mBq/kg) 60 Co (mBq/kg) Pure Iron< 0.6< 0.8< 0.4 Pure iron does not rust Cheaper than SS Single recoils from: Electron recoils (vessel - 2 cm thick) U < 0.6 mBq/kg< Th < 0.8 mBq/kg< K < 5 mBq/kg< Co: 1.7 mBq/kg73100 Sum < < 1.5 x 10 5 Would need a rejection factor ~ 10 5 if no external shielding