Background studies for EURECA
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Transcript of Background studies for EURECA
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
Residual background
Edelweiss (fid. volume Ge) 3 evts/kg.d 1 / 105 1 / 30 000 kg.d
EURECA Ge 0.3 evts/kg.d 1 / 105 1 / 300 000 kg.d
Pia Loaiza AARM 19-20 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 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
Element C Si Mn P S Cr Mo Ni Ti
Min (%) 16.5 2.0 10.5 (5xC)
Max (%) 0.08 1.00 2.00 0.045 0.015 18.5 2.5 13.5 0.7
Pia Loaiza AARM 19-20 March 2010
Sample G2 G3 G5 G6
Vendor Ilsenburg Ugine&Alz Acroni Ilsenburg228Ra (mB/kg) < 0.86 < 1 1.0 0.5 < 1.1
228Th (mB/kg) <0.11 < 0.41 1.5 0.2 <0.27
226Ra (mB/kg) <0.24 < 0.74 1.0 0.6 <0.35
234mPa (mB/kg) <12 < 45 54 16 <38
235U (mB/kg) <0.63 < 1.5 2.5 1.5 < 1.5
40K (mB/kg) <0.93 < 1.1 < 0.81 < 1.1
60Co (mB/kg) 14.0 0.1 13.8 0.7 18.3 0.7 13 0.6
137Cs (mB/kg) <0.16 <0.36 < 0.1 <0.39
7Be (mB/kg) <3 <5.7 4.8 1.7 13 2.5
54Mn (mB/kg) 1.50.1 0.92 0.24 1.7 0.2 1.4 0.2
58Co (mB/kg) 0.99 0.12 0.56 0.23 0.69 0.16 0.59 0.2
56Co (mB/kg) 0.17 0.06 <0.62 0.28 0.10 <0.42
46Sc (mB/kg) 0.24 0.06 <0.54 0.47 0.14 <0.31
48V (mB/kg) 0.36 0.07 0.27 0.11 0.22 0.09 0.40 0.12
U < 1 mBq/kg, Th < 1 mBq/kg, 40K < 1 mBq/kg, 60Co ~ 10 mBq/kg
Pia Loaiza AARM 19-20 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 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