Transcript Diapositive 1 - University of Minnesota

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
Laboratoire Souterrain de Modane
Deepest underground laboratory in
Europe: 4800 m.w.e
2nd deepest underground in the world
Canfranc
Located in the Fréjus tunnel at the
french-italian border
Modane
Operated by CNRS and CEA
Pia Loaiza AARM-Berkeley 19-20 March 2010
Entrance tunnel
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
Primordial Radionuclides
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-1
E > 1 MeV
238U
232Th
subm. To J. Phys. G:
Nucl. Phys.
Radon concentration
K
0.84 ppm
Rock
1.9 ppm
Concrete
2.45 ppm
Rock
1.4 ppm
Concrete
213 Bq/kg
Rock
77 Bq/kg
Concrete
Astrop. Phys. 9 (1998) 163
5 to 15 Bq/m3
Pia Loaiza AARM-Berkeley 19-20 March 2010
Radon reduction facility
Principle:
Time during which radon is trapped
in the « filter » : Tr = K(T) M / Q
K(T) : dynamic adsorption coeff.
M : charcoal mass
Q : Air rate
2 charcoal towers :
T1 = -53 C, T2 = -45 C
M = 2 x 450 kg
HPGe’s
Output:
Vol. clean air : 125 m3/h
Activity 222Rn = 15 mBq/m3
Same as Kamioka system
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 19-20 March 2010
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
HPGe’s internal background
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
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)
Pulse-tube
Crystal dimensions:
 = 80 mm
h=30 mm
Vol = 150 cm3
Mass=0.8 kg
Suited for E < 600 keV
Good resolution at low energies
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
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
Where do we stand in terms of sensibility?
Example of measurements at LSM:
Mafalda detector-planar:
Sample
Mass
(g)
Time
(h)
210Pb
234Th
226Ra
228Ra
228Th
(mBq/kg)
(mBq/kg)
(mBq/kg)
(mBq/kg)
(mBq/kg)
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
137Cs
226Ra
228Ra
228Th
(mBq/kg)
(mBq/kg)
(µBq/kg)
(µBq/kg)
(µBq/kg)
2500
768
< 1.5
< 0.1
< 135
< 274
< 174
2373
869
< 1.5
< 0.3
< 170
< 274
< 166
GLUE 1
GLUE 2
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
SuperNEMO
40 mBq/kg in 214Bi
3 mBq/kg in 228Th
2 Bq/kg 208Tl
10 Bq/kg 214Bi
needed for PMTS
double beta sources
Specific
detector
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
Sharing knowledge
We know it’s possible to get a sensitivity of 20 Bq/kg
Our colleagues from Gran Sasso have obtained:
Material
Copper
Weight
125 kg
days
100.7
226Ra
228Th
Bq/kg
Bq/kg
<16
<19
40K
60Co
Bq/kg
Bq/kg
<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 measurements
Example: the BiPo detector for SuperNEMO
•
Measurement of
•
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 
•
208Tl
and 214Bi concentration in foil-sources and other thin materials
-
Plastic scintillateurs

Source foil
Pia Loaiza AARM-Berkeley 19-20 March 2010