Pia Loaiza AARM-Berkeley 19-20 March 2010

Low background gamma spectrometry at the Laboratoire Souterrain de Modane

The LSM laboratory

HPGe detectors development at LSM

LSM HPGe detectors’s performance

Costs

Future needs in gamma spectrometry

Pia Loaiza AARM-Berkeley 19-20 March 2010

CanfrancCanfranc

Modane

Laboratoire Souterrain de Modane

Deepest underground laboratory in Europe: 4800 m.w.e

2nd deepest underground in the world

Located in the Fréjus tunnel at the french-italian border

Entrance tunnel

Operated by CNRS and CEA

Pia Loaiza AARM-Berkeley 19-20 March 2010

Primordial Radionuclides

Rock213 Bq/kgK

Concrete1.4 ppm

Concrete1.9 ppm

Concrete77 Bq/kg

Rock2.45 ppm232Th

Rock0.84 ppm238U

Primordial Radionuclides

Rock213 Bq/kgK

Concrete1.4 ppm

Concrete1.9 ppm

Concrete77 Bq/kg

Rock2.45 ppm232Th

Rock0.84 ppm238U

5 to 15 Bq/m3

Radon concentration

Total Vol: 3500 m3

Ge room: 70 m2:

+ 2 secondaries: hall of 18 m2 and 21m2

Neutron flux(3.570.05stat0.27sys )x 10-6 n cm-2 s-1 thermal(1.1 0.1stat) x 10-6 n cm-2 s-1 E > 1 MeV

NIM A262 (1987) 463 Muon Flux 4.2 m-2 d-1 (5.14 ± 0.39) 10-9 cm-2 s-1

Astrop. Phys. 9 (1998) 163

subm. To J. Phys. G: Nucl. Phys.

Main hall30m x 10 m x 10m

Pia Loaiza AARM-Berkeley 19-20 March 2010

Time during which radon is trappedin the « filter » : Tr = K(T) M / Q

K(T) : dynamic adsorption coeff.M : charcoal massQ : Air rate

2 charcoal towers : T1 = -53 C, T2 = -45 CM = 2 x 450 kg

Vol. clean air : 125 m3/hActivity 222Rn = 15 mBq/m3

Radon reduction facility

Output:

Principle:

Same as Kamioka system

HPGe’s

Pia Loaiza AARM-Berkeley 19-20 March 2010

• Material screening for EDELWEISS, SuperNEMO and ultra low background instrumentation.

HPGe Gamma-spectrometers at LSM 13 HPGe detectors for:

Pia Loaiza AARM-Berkeley 19-20 March 2010

7Be and 137Cs concentration in the atmosphere

Monitoring of radioactive contamination in the atmosphere

Measurements of artificial radionuclides in certainsamples require very low backgrounds. Those measurements are carried out at the LSM.

• Measurement of environmental radioactivity Radionuclides in the U and Th decay series are useful chronometers for the determination of many processes in the environment. The low natural radioactivity encountered necessitate instrumentation capable of measuring very low radionuclide concentrations.Some applications :

Quantitative evaluation of both horizontal and vertical mixing rates in the open ocean.

Determination of the rate of particle deposition on the marine sediment layer (originated by both biological and physical processes).

The decay of 210Pb provides a dating method which has been applied to lake sediments.

Environmental studies

Pia Loaiza AARM-Berkeley 19-20 March 2010

Detector Type Volume Total and peak background rate (counts/day)

40-2700 keV 352 keV 583 keV 1461 keV

MONDEUSE well 220 cc 770 4.2 2.7 5

ROUSSETE well 430 cc 692 4.1 2.9 7.2

ABYMES well 980 cc 828 5.6 5.6 5.6

XXL well 844 cc 821 6.8 <1.8 11.6

HERMINE N 197 cc 313 1.2 1.5 2.3

HELLAZ P 204 cc 515 4.5 0.5 1.4

JASMIN P 380 cc 529 2.0 1.41 1.71

GENTIANE N 215 cc 178 < 0.21 0.38 0.65

IRIS P 400 cc 282 1.02 1.46 3.01

MAFALDA plan 150 cc 150 < 0.3 < 0.3 < 0.4

HPGe’s internal background

Pia Loaiza AARM-Berkeley 19-20 March 2010

Collaboration with CANBERRA and CENBG (Centre d’Etudes Nucléaires de Bordeaux Gradignan)

Crystal dimensions: = 80 mm h=30 mm Vol = 150 cm3

Mass=0.8 kg

We use a pulse-tube to cool down instead of liquid Nitrogen (for the first time in a HPGe in LSM)

Suited for E < 600 keVGood resolution at low energies

Pulse-tube controller

Pulse-tube

HPGe detectors development : Planar HPGe

5 cm archeological lead, 210Pb < 0.1 Bq/kg15 cm Pb standard lead , approx 10-20 Bq/kg

SELECTION OF ALL MATERIALSMODIFIED CONFIGURATION

Pia Loaiza AARM-Berkeley 19-20 March 2010

Performances

Resolution: 850 eV at 122 keVIntegral count rate 20 keV <E < 1500 keV : 150 cpd

All peak-rates < 1 c/day, except 210Pb

Pia Loaiza AARM-Berkeley 19-20 March 2010

Where do we stand in terms of sensibility?Example of measurements at LSM:

Sample Mass(g)

Time(h)

40K(mBq/kg)

137Cs(mBq/kg)

226Ra(µBq/kg)

228Ra(µBq/kg)

228Th(µBq/kg)

GLUE 1 2500 768 < 1.5 < 0.1 < 135 < 274 < 174

GLUE 2 2373 869 < 1.5 < 0.3 < 170 < 274 < 166

IRIS detector-coaxial, measurements by Abdel Nachab for SuperNEMO coll.:

Sample Mass(g)

Time(h)

210Pb(mBq/kg)

234Th(mBq/kg)

226Ra(mBq/kg)

228Ra(mBq/kg)

228Th(mBq/kg)

Aluminium 1025 132 < 9 <3 <0.9 <1 1.00.3

Epoxy 47 384 357 143 92 < 6 103

Mafalda detector-planar:

Pia Loaiza AARM-Berkeley 19-20 March 2010

Costs

Detector with dedicated low-background developpement: between 100 kEuro and 200 kEuro, depending on crystal mass, cooling system,…

Shielding: Archeological lead: about 200-250 Euros/kg, Low activity lead: about 2 Euros/kg

Lead casting: around 20 kEuros

Commercial acquisition system (hardware + software) : about 10 kEuro

Pia Loaiza AARM-Berkeley 19-20 March 2010

Which sensitivities for the future experiments?

EURECA: • Present rejection factor ~ 105

• According to simulations: ~105 evts/year in 10 keV<E<50 keV in 1000 kg of Ge from Cu 226Ra, 228Th : 20 Bq/kg

Need to gain around factor 3 in sensibility to reach 20 Bq/kg in CuTime-consuming measurements : 2 to 3 months

need more detectors

SuperNEMO 40 mBq/kg in 214Bi 3 mBq/kg in 228Th needed for PMTS

further reduction of background

2 Bq/kg 208Tl 10 Bq/kg 214Bi double beta sources

Specificdetector

Pia Loaiza AARM-Berkeley 19-20 March 2010

Sharing knowledge

We know it’s possible to get a sensitivity of 20 Bq/kgOur colleagues from Gran Sasso have obtained:

Material Weight days 226RaBq/kg

228Th Bq/kg

40KBq/kg

60CoBq/kg

Copper 125 kg 100.7 <16 <19 <88 <10

Today:- sharing knowledege on ‘good materials’- on clean methods for cutting, shaping pieces

Pia Loaiza AARM-Berkeley 19-20 March 2010

Summary

Long tradition at LSM for development of low-background HPGe detectors

Sensitivities at LSM today ~ 10 mBq/kg 210Pb, 3 mBq/kg 238U (234Th) – planar detector ~200 Bq/kg for 226Ra, 228Th – coaxial detector

Sensitvities needed for future experiments, namely EURECA ~10 Bq/kg

Need further reduction of intrinsic background

Taking into account the Gran Sasso experience, the sensitivities needed are reacheable

Pia Loaiza AARM-Berkeley 19-20 March 2010

Detector-specific radioctivity measurementsExample: the BiPo detector for SuperNEMO

• Measurement of 208Tl and 214Bi concentration in foil-sources and other thin materials

• Goal : measurement of 10 m2 of foil-sources (40 mg/cm2) in 1 month with sensibility :– Volume concentrations : 208Tl < 2 Bq/kg & 214Bi < 10 Bq/kg– Surface concentrations : 208Tl < 0.1 Bq/m2 & 214Bi < 0.5 Bq/m2

• Detection of the BiPo cascade : + delayed

Plastic scintillateurs Source foil