LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 Low-level techniques applied in experiments looking for rare events Germanium spectrosco py Grzegorz Zuzel Max Planck Institute for Nuclear Physics, Heidelberg, Germany Radon detection Mass spectromet ry Conclusion s Introducti on
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LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 Low-level techniques applied in experiments.
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LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
Low-level techniques applied in experiments looking for
rare eventsGermanium spectroscopy
Grzegorz ZuzelMax Planck Institute for Nuclear Physics, Heidelberg, Germany
Radon detection
Mass spectrometry
Conclusions
Introduction
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
1. Introduction
Low-level techniques: experimental techniques which allow to investigate very low activities of natural and artificially produced radio-isotopes.
• material screening (Ge spectroscopy, ICPMS, NA)• surface screening (,, spectroscopy)• study of radioactive noble gases (emanation, diffusion)• purification techniques (gases, liquids)• background events rejection techniques• modeling of background in experiments (Monte Carlo)
Low-level techniques are “naturally” coupled with the experiments looking for rare events (detection of neutrinos, search for dark matter, search for 0ν2 decay, search for proton decay, ...), where the backgrounds identification and reduction plays a key role.
Germanium spectroscopy
Radon detection
Mass spectrometry
Conclusions
Introduction
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
2. Germanium spectroscopy
Germanium spectroscopy
Radon detection
Mass spectrometry
Conclusions
Introduction
Germanium spectroscopy is one of the most powerful techniques to identify γ-emmiters (U/Th chain, 40K, 60Co,...).
• excellent energy resolution (~ 2 keV)• high purity detectors (low intrinsic background)
In order to reach high sensitivity it is necessary:
• reduce backgrounds originating from external sources - active/passive shielding (underground localizations) - reduction of radon in the sample chamber
• assure (reasonably) large volumes of samples• assure precise calculations/measurements of detection efficiencies
Highly sensitive Ge spectroscopy is a perfect tool for material screening
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
2. Germanium spectroscopy
Germanium spectroscopy
Radon detection
Mass spectrometry
Conclusions
Introduction
GeMPIs at GS (3800 m w.e.)
• GeMPI I operational since 1997 (MPIK)• GeMPI II built in 2004 (MCavern)• GeMPI III constructed in 2007
(MPIK/LNGS) • Worlds most sensitive spectrometers
GeMPI I:
• Crystall: 2.2 kg, r = 102 %
• Bcg. Index (0.1-2.7 MeV): 6840 cts/kg/year• Sample chamber: 15 l
Sensitivity:~10 Bq/kg
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
2. Germanium spectroscopy
Germanium spectroscopy
Radon detection
Mass spectrometry
Conclusions
Introduction
Detectors at MPI-K: Dario, Bruno and Corrado
Sensitivity:~1 mBq/kg
MPI-K LLL: 15 m w.e.
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
2. Germanium spectroscopy
Germanium spectroscopy
Radon detection
Mass spectrometry
Conclusions
Introduction
Selected results: steel for the GERDA cryostat (MPIK/LNGS)
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
3. Radon detection
Germanium spectroscopy
Radon detection
Mass spectrometry
Conclusions
Introduction
Radon 222Rn and its daughters form one of the most dangerous source of background in many experiments
• inert noble gas• belongs to the 238U chain (present in any material)• high diffusion and permeability• wide range of energy of emitted radiation (with the daughters)• surface contaminations with radon daughters (heavy metals)• broken equilibrium in the chain at 210Pb level
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
3. Radon detection
Germanium spectroscopy
Radon detection
Mass spectrometry
Conclusions
Introduction
Proportional counters
• Developed for the GALLEX/GNO experiment• Hand-made at MPI-K (~ 1 cm3 active volume)• In case of 222Rn only α-decays are detected • 50 keV threshold - bcg: 0.1 – 2 cpd - total detection efficiency of ~ 1.5• Absolute detection limit ~ 30 µBq (15 atoms)
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
3. Radon detection
Germanium spectroscopy
Radon detection
Mass spectrometry
Conclusions
Introduction
222Rn in gases (N2/Ar) - MoREx
222Rn detection limit: ~0.5 Bq/m3 (STP)
[1 atom in 4 m3]
• 222Rn adsorption on activated carbon• several AC traps available (MoREx/MoRExino)• pre-concentration from 100 – 200 m3
• purification is possible (LTA)
A combination of 222Rn pre-concentration and low-background counting gives the most sensitive technique for radon detection in gases
222Rn/226Ra in water - STRAW
222Rn detection limit: ~0.1 mBq/m3
226Ra detection limit: ~0.8 mBq/m3
• 222Rn extraction from 350 liters• 222Rn and 226Ra measurements possible
Great importance for BOREXINO, GERDA, EXO, XENON, XMASS, WARP, CLEAN, …
Production rate: 100 m3/h222Rn ≤0.5 Bq/m3 (STP)
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
3. Radon detection
Germanium spectroscopy
Radon detection
Mass spectrometry
Conclusions
Introduction
222Rn emanation and diffusion
Absolute sensitivity ~100 Bq [50 atoms]
Blanks:20 l 50 Bq 80 l 80 Bq
Sensitivity ~ 10-13 cm2/s
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
• 222Rn monitoring in gases• Shape adopted to the electrical field• Volume: 750 l• Sensitivity goal: ~ 50 Bq/m3
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
3. Radon detection
Germanium spectroscopy
Radon detection
Mass spectrometry
Conclusions
Introduction
222Rn daughters on surfaces (M. Wojcik)
• Screening of 210Po with an alpha spectrometer 50 mm Si-detector, bcg ~ 5 /d (1-10 MeV) sensitivity ~ 20 mBq/m2 (100 mBq/kg, 210Po)
• Screening of 210Bi with a beta spectrometer 250 mm Si(Li)-detectors, bcg ~ 0.18/0.40 cpm sensitivity ~ 10 Bq/kg
• Screening of 210Pb (46.6 keV line) with a gamma spectrometer 25 % - n-type HPGe detector with an active and a passive shield sensitivity ~ 20 Bq/kg
• Only small samples can be handled – artificial contamination needed: e.g. discs loaded with 222Rn daughters
Copper cleaning tests
• Etching removes most of 210Pb and 210Bi (> 98 %) but not 210Po• Electropolishing is more effective for all elements but proper conditions have to be found (e.g. 210Po reduction from 30 up to 200)