Low background gamma spectrometry at the Laboratoire Souterrain de Modane

1. 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

2. Entrance tunnel 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 Modane Operated by CNRS and CEA Pia Loaiza AARM-Berkeley 19-20 March 2010

3. Total Vol: 3500 m3 Ge room: 70 m2: + 2 secondaries: hall of 18 m2 and 21m2 Main hall 30m x 10 m x 10m Muon Flux 4.2  m-2 d-1 (5.14 ± 0.39) 10-9cm-2 s-1 NIM A262 (1987) 463 Neutron flux (3.570.05stat0.27sys )x 10-6 n cm-2 s-1 thermal (1.1 0.1stat)x 10-6 n cm-2 s-1E > 1 MeV subm. To J. Phys. G: Nucl. Phys. Radon concentration Astrop. Phys. 9 (1998) 163 5 to 15 Bq/m3 Pia Loaiza AARM-Berkeley 19-20 March 2010

4. Radon reduction facility Principle: HPGe’s Output: Same as Kamioka system Pia Loaiza AARM-Berkeley 19-20 March 2010

5. HPGe Gamma-spectrometers at LSM 13 HPGe detectors for: • Material screening for EDELWEISS, SuperNEMO and ultra low background instrumentation. Pia Loaiza AARM-Berkeley 19-20 March 2010

6. Environmental studies • 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. Monitoring of radioactive contamination in the atmosphere Measurements of artificial radionuclides in certain samples require very low backgrounds. Those measurements are carried out at the LSM. 7Be and 137Cs concentration in the atmosphere Pia Loaiza AARM-Berkeley 19-20 March 2010

7. HPGe’s internal background Pia Loaiza AARM-Berkeley 19-20 March 2010

8. HPGe detectors development : Planar HPGe 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 Suited for E < 600 keV Good resolution at low energies Pulse-tube SELECTION OF ALL MATERIALS MODIFIED CONFIGURATION Pulse-tube controller We use a pulse-tube to cool down instead of liquid Nitrogen (for the first time in a HPGe in LSM) 5 cm archeological lead, 210Pb < 0.1 Bq/kg 15 cm Pb standard lead , approx 10-20 Bq/kg Pia Loaiza AARM-Berkeley 19-20 March 2010

9. Performances Resolution: 850 eV at 122 keV Integral 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

10. Where do we stand in terms of sensibility? Example of measurements at LSM: Mafalda detector-planar: IRIS detector-coaxial, measurements by Abdel Nachab for SuperNEMO coll.: Pia Loaiza AARM-Berkeley 19-20 March 2010

11. 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

12. 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 SuperNEMO 40 mBq/kg in 214Bi 3 mBq/kg in 228Th needed for PMTS Specific detector 2 Bq/kg 208Tl 10 Bq/kg 214Bi double beta sources Need to gain around factor 3 in sensibility to reach 20 Bq/kg in Cu Time-consuming measurements : 2 to 3 months need more detectors further reduction of background Pia Loaiza AARM-Berkeley 19-20 March 2010

13. Sharing knowledge We know it’s possible to get a sensitivity of 20 Bq/kg Our colleagues from Gran Sasso have obtained: Today: - sharing knowledege on ‘good materials’ - on clean methods for cutting, shaping pieces Pia Loaiza AARM-Berkeley 19-20 March 2010

14. 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

15. 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  Detector-specific radioctivity measurements Example: the BiPo detector for SuperNEMO b- a Plastic scintillateurs Source foil Pia Loaiza AARM-Berkeley 19-20 March 2010