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