Pia Loaiza AARM 19-20 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
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Pia Loaiza AARM 19-20 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 19-20 March 2010
• 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
• Preferred site: 60 000 m3 extension of present LSM (4 /m2/d), to be dug
in 2011-2012
EURECA
Pia Loaiza AARM 19-20 March 2010
0 events
-equivalentto ~103 kgd
arXiv:0905.0753 accepted by PLB
Gamma
Rejection better than 1 in 105
EDELWEISS II: GAMMA REJECTION
Pia Loaiza AARM 19-20 March 2010
HALL B: DARK MATTER (EURECA TYPE)H
all B
120
00 m
3
Approx. dimensions:18x15x50 m
Internal dimensions (2400 m3):11x6x46 m
water
wat
er
First shielding configuration: the ‘submarine’ design
Pia Loaiza AARM 19-20 March 2010
STAINLESS STEEL 226Ra 228Th 40K 60Co SUM
Borexino
Steel for flanches
Astrop. Phys. 18, 1 (2002)
A (mBq/kg)
6.2 1.2 6.5 1.6 < 13 14 1
Single e- recoils
270000 304000 < 30000 600000 1208000
Double Chooz
Outkumpu
P. Loaiza
A (mBq/kg)
5 2 5.5 1.3 < 15 14 2
Single e- recoils
216000 260000 <34000 600000 1114000
Edelweiss
304L
C. Goldbach, G. Nollez
A (mBq/kg)
4 2 5 2 14 10 14 3
Single e- recoils
173000 224000 32000 600000 1032000
GERDA
Ugine&Alz
1.4571 - 316TiW. Maneschg et alNIM A 593, 448 (2008)
A (mBq/kg)
< 0.74 < 0.41 < 1.1 13.8 0.7
Single e- recoils
< 32000 <19100 < 2500 593000 648000
XENON
Fábrica del Campo de
Gibraltar, Cádiz
316Ti
From L. Baudis, IDM08
A (mBq/kg)
< 1.3 < 0.9 < 7.1 1.4
Single e- recoils
57000 <42000 < 16000 60200 176000
Events from 2cm thick water-tank per 100 kg Ge per year , 10 keV <Er< 50 keV
~2 ·105
Simulations by V. Kudryavtsev et al
Pia Loaiza AARM 19-20 March 2010
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
‘Pool’ configuration
Preliminary layout, to be evolved
By CEA/IRFU
Pia Loaiza AARM 19-20 March 2010
cryostat
Cold
Signalsin/out
Amplis
Pure water
Radiation level-gamma-neutron
-neutron
neutron
gamma
Pia Loaiza AARM 19-20 March 2010
Attenuation of gamma-rays by water
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
Plot by V. Kudryavtsev et al
Pia Loaiza AARM 19-20 March 2010
238U 232Th 40K 60Co
A (ppb) 0.01 0.01 10 1 mBq/kg
Single e- recoils/year
1.9 ·105 4 ·105
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:
Copper 226Ra 228Th 40K 60Co SUM
NOSV
G. Heusser, LRT2004
A (Bq/kg) < 20 < 23 < 90 < 10
Single e- recoils/year
~ 2 ·104 ~ 4 ·103 ~ 2 ·104
Which translates to:
→ roughly, we need the previous Cu purity to get acceptable backg levels
Pia Loaiza AARM 19-20 March 2010
Beta background and rejection
arXiv:0905.0753v1
EDELWEISS II: beta calibration with a 210Pb source:
Beta background Level of 210Pb backg in ROI ID rejection factor
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
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 alW. Manesch, H. Simgen: Private comm.
Commonly available stainless steel : 1.4571 - 316Ti has very low concentrations in primordial radionuclides(Mo content allows high corrosion resistance)
Measurement campaign in collaboration with trading company NironitSamples from different European manufacturers
For easier comparison activities are given as U, Th and K concentrations. For the conversion of 226Ra into U and 228Th into Th secular equilibriumwas assumed although this is seldom the case
Concentrations in SS used in previous experiments
Collab. Ref. / measure Description 238U (ppb)
mBq/kg
232Th
(ppb)
mBq/kg
natK
(ppm)
mBq/kg
60Co
(mBq/kg)
BOREXINO Ast.Phys. 18, 1, 2002
AISI304L for SSS 0.370.07
4.60.9
2.80.3
11.41.1
< 0.45
< 14
61
Steel for flanges 0.50.1
6.21.2
1.60.4
6.5 1.6
< 0.42
<13
141
Steel for storage vessel
1.40.2
173
0.90.6
3.82.6
<0.6
<19
122
Steel TK3B for storage vessel
0.40.1
51
1.20.5
52
0.130.06
4 2
463
DOUBLE CHOOZ
P. Loaiza Outokumpu 0.410.16
52
1.40.3
5.5 1.3
<0.47
<15
142
EDW C. Goldbag and G. Nollez
304L 0.320.16
42
1.2 0.5
5 2
0.450.32
14 10
143
Pia Loaiza AARM 19-20 March 2010
Pia Loaiza AARM 19-20 March 2010
‘Xenon stainless steel’ 316Ti steel
Provider: Nironit Edelstahlhandel 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 sincethe 60Co content may vary with charge number
Pia Loaiza AARM 19-20 March 2010
NEMO 3/SUPERNEMO PURE IRONIron 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 214Bi (226Ra)
(mBq/kg)
208Tl
(228Th)
(mBq/kg)
40K
(mBq/kg)
60Co
(mBq/kg)
Pure Iron < 0.6 < 0.8 < 5 1.70.4
Pure iron does not rust
Cheaper than SS
Single recoils from:
Electron recoils
(vessel - 2 cm thick)
U < 0.6 mBq/kg < 26390
Th < 0.8 mBq/kg < 37400
40K < 5 mBq/kg < 11565
60Co: 1.7 mBq/kg 73100
Sum< 148455
< 1.5 x 105
Would need a rejection factor ~ 105 if no external shielding