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


• 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


0 events

-equivalentto ~103 kgd

arXiv:0905.0753 accepted by PLB

Gamma

Rejection better than 1 in 105

EDELWEISS II: GAMMA REJECTION


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


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


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


‘Pool’ configuration

Preliminary layout, to be evolved

By CEA/IRFU


cryostat

Cold

Signalsin/out

Amplis

Pure water

Radiation level-gamma-neutron

-neutron

neutron

gamma


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


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


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


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


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


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


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



‘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


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

Documents

Background studies for EURECA