1. 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 March 2010

2. Pia Loaiza AARM-Berkeley 19-20 March 2010
Laboratoire Souterrain de Modane
Deepest underground laboratory in
Europe: m.w.e
2nd deepest underground in the world
Located in the Fréjus tunnel at the french-italian border
Entrance tunnel
Modane
Operated by CNRS and CEA
Pia Loaiza AARM-Berkeley March 2010

3. Pia Loaiza AARM-Berkeley 19-20 March 2010
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) 10-9 cm-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 E > 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 March 2010

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

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

6. Monitoring of radioactive contamination in the atmosphere
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 March 2010

7. Pia Loaiza AARM-Berkeley 19-20 March 2010
HPGe’s internal background
Detector
Type
Volume
Total and peak background rate (counts/day)
keV
352 keV
583 keV
1461 keV
MONDEUSE
well
220 cc
770
4.2
2.7 5
ROUSSETE
430 cc
692
4.1
2.9
7.2
ABYMES
980 cc
828
5.6
XXL
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
380 cc
529
2.0
1.41
1.71
GENTIANE
215 cc
178
< 0.21
0.38
0.65
IRIS
400 cc
282
1.02
1.46
3.01
MAFALDA
plan
150 cc
150
< 0.3
< 0.4
Pia Loaiza AARM-Berkeley March 2010

8. Pia Loaiza AARM-Berkeley 19-20 March 2010
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 Bq/kg
Pia Loaiza AARM-Berkeley March 2010

9. Pia Loaiza AARM-Berkeley 19-20 March 2010
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 March 2010

10. Pia Loaiza AARM-Berkeley 19-20 March 2010
Where do we stand in terms of sensibility?
Example of measurements at LSM:
Mafalda detector-planar:
Sample
Mass
(g)
Time
(h)
210Pb
(mBq/kg)
234Th
226Ra
228Ra
228Th
Aluminium
1025
132
< 9
<3
<0.9
<1
1.00.3
Epoxy 47
384
357
143
92
< 6
103
IRIS detector-coaxial, measurements by Abdel Nachab for SuperNEMO coll.:
Sample
Mass
(g)
Time
(h)
40K
(mBq/kg)
137Cs
226Ra
(µBq/kg)
228Ra
228Th
GLUE 1
2500
768
< 1.5
< 0.1
< 135
< 274
< 174
GLUE 2
2373
869
< 0.3
< 170
< 166
Pia Loaiza AARM-Berkeley March 2010

11. 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 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 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 March 2010

13. Pia Loaiza AARM-Berkeley 19-20 March 2010
Sharing knowledge
We know it’s possible to get a sensitivity of 20 Bq/kg
Our colleagues from Gran Sasso have obtained:
Material
Weight
days
226Ra
Bq/kg
228Th Bq/kg
40K
60Co
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 March 2010

14. 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 March 2010

15. Detector-specific radioctivity measurements
Example: 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  b- a
Plastic scintillateurs
Source foil
Pia Loaiza AARM-Berkeley March 2010