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Background studies for EURECA

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. EURECA.

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Background studies for EURECA

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  1. 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 19-20 March 2010

  2. EURECA • 10-10 pb goal = no background in 150 000 kg.d • Joint effort from teams from EDELWEISS, CRESST, ROSEBUD, CERN, + others… • >>100 kg cryogenic experiment, multi-target • Part of ILIAS/ASPERA European Roadmap • Preferredsite: 60 000 m3 extension of present LSM (4 /m2/d), to be dug in 2011-2012 Pia Loaiza AARM 19-20 March 2010

  3. EDELWEISS II: GAMMA REJECTION -equivalent to ~103 kgd Rejection better than 1 in 105 0 events arXiv:0905.0753 accepted by PLB Gamma Pia Loaiza AARM 19-20 March 2010

  4. First shielding configuration: the ‘submarine’ design HALL B: DARK MATTER (EURECA TYPE) water water Hall B 12000 m3 Internal dimensions (2400 m3): 11x6x46 m Approx. dimensions: 18x15x50 m Pia Loaiza AARM 19-20 March 2010

  5. Events from 2cm thick water-tank per 100 kg Ge per year , 10 keV <Er< 50 keV Simulations by V. Kudryavtsev et al ~2 ·105 Pia Loaiza AARM 19-20 March 2010

  6. Gamma background from stainless steel water tank for the ‘submarine’ configuration • 10-10 pb goal = no background in 150 000 kg.d • from stainless steel water-tank: 2 ·105 evts/100 kg year = 8 ·105 evts in 150 000 kg.d • Gamma rejection factor in EDWII : 1 in 105 Untolerable gamma background Pia Loaiza AARM 19-20 March 2010

  7. ‘Pool’ configuration Preliminary layout, to be evolved By CEA/IRFU Pia Loaiza AARM 19-20 March 2010

  8. cryostat Pure water -neutron Radiation level -gamma -neutron gamma Cold Amplis neutron Signals in/out Pia Loaiza AARM 19-20 March 2010

  9. Attenuation of gamma-rays by water Plot by V. Kudryavtsev et al • Swimming-pool: without water, comparable e recoil event rate expected wrt ‘submarine’ design • Around factor 106 - 107 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 Pia Loaiza AARM 19-20 March 2010

  10. 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), 10-50 keV: Which translates to: → roughly, we need the previous Cu purity to get acceptable backg levels Pia Loaiza AARM 19-20 March 2010

  11. Beta background and rejection EDELWEISS II: beta calibration with a 210Pb source: arXiv:0905.0753v1 Pia Loaiza AARM 19-20 March 2010

  12. 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 19-20 March 2010

  13. Measurements of extremely low radioactivity levels in stainless steel for GERDA NIM A Vol. 593, 448 (2008) , W. Maneschg et al W. Manesch, H. Simgen: Private comm. Amount of costly copper to be used depends drastically on the contamination of stainless steel Measurement campaign in collaboration with trading company Nironit Samples from different European manufacturers Commonly available stainless steel : 1.4571 - 316Ti has very low concentrations in primordial radionuclides (Mo content allows high corrosion resistance) Pia Loaiza AARM 19-20 March 2010

  14. U < 1 mBq/kg, Th < 1 mBq/kg, 40K < 1 mBq/kg, 60Co ~ 10 mBq/kg Pia Loaiza AARM 19-20 March 2010

  15. Concentrations in SS used in previous experiments 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 Pia Loaiza AARM 19-20 March 2010

  16. Pia Loaiza AARM 19-20 March 2010

  17. ‘Xenon stainless steel’ 316Ti steel Provider: NironitEdelstahlhandel GmbH & Co. KG Producer: Fábrica del Campo de Gibraltar, Cádiz Grade of the material : X6CrNiMoTi17-12-2. Works Grade : ACX -280.  Need to scan the samples since the 60Co content may vary with charge number Pia Loaiza AARM 19-20 March 2010

  18. 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. Pure iron does not rust Cheaper than SS Would need a rejection factor ~ 105 if no external shielding Pia Loaiza AARM 19-20 March 2010

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