Transcript A large volume detector for 222Rn in gas

Introduction
Germanium
spectroscopy
Radon detection
Low-level techniques applied
in experiments looking for
rare events
Mass
spectrometry
Grzegorz Zuzel
Conclusions
Max Planck Institute for Nuclear Physics, Heidelberg, Germany
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.
Introduction
Germanium
spectroscopy
Radon detection
Mass
spectrometry
Conclusions
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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.
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
2. Germanium spectroscopy
Germanium spectroscopy is one of the most powerful techniques to
identify γ-emmiters (U/Th chain, 40K, 60Co,...).
Introduction
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excellent energy resolution (~ 2 keV)
high purity detectors (low intrinsic background)
Germanium
spectroscopy
Radon detection
In order to reach high sensitivity it is necessary:
Mass
spectrometry
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reduce backgrounds originating from external sources
- active/passive shielding (underground localizations)
- reduction of radon in the sample chamber
Conclusions
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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
GeMPIs at GS (3800 m w.e.)
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Introduction
Germanium
spectroscopy
Radon detection
Mass
spectrometry
Conclusions
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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
Detectors at MPI-K: Dario, Bruno and Corrado
Introduction
Germanium
spectroscopy
Radon detection
Mass
spectrometry
Conclusions
MPI-K LLL: 15 m w.e.
Sensitivity:
~1 mBq/kg
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
2. Germanium spectroscopy
Selected results: different materials
Introduction
228Th
226Ra
40K
Copper
≤ 0.012
≤ 0.016
≤ 0.088
Lead
DowRun
≤ 0.022
≤ 0.029
0.044  0.014
(27 4)103
Mass
spectrometry
Ancient lead
≤ 0.072
≤ 0.045
≤ 0.27
≤ 1300
Conclusions
Kapton cable
Germanium
spectroscopy
Radon detection
Teflon
0.023  0.015 0.021  0.009
≤4
96
210Pb
0.54  0.11
130  60
Specific activities in [mBq/kg]
G. Heusser et al.
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
2. Germanium spectroscopy
Selected results: steel for the GERDA cryostat (MPIK/LNGS)
Introduction
Germanium
spectroscopy
Radon detection
Mass
spectrometry
Conclusions
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
3. Radon detection
Radon 222Rn and its daughters form one of the most dangerous
source of background in many experiments
Introduction
Germanium
spectroscopy
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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
Radon detection
Mass
spectrometry
Conclusions
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
3. Radon detection
Proportional counters
Introduction
Germanium
spectroscopy
Radon detection
Mass
spectrometry
Conclusions
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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
222Rn
Introduction
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Germanium
spectroscopy
in gases (N2/Ar) - MoREx
222Rn
adsorption on activated carbon
several AC traps available (MoREx/MoRExino)
pre-concentration from 100 – 200 m3
purification is possible (LTA)
222Rn
detection limit:
~0.5 Bq/m3 (STP)
[1 atom in 4 m3]
A combination of 222Rn pre-concentration and low-background
counting gives the most sensitive technique for radon detection in gases
Radon detection
Great importance for BOREXINO, GERDA,
EXO, XENON, XMASS, WARP, CLEAN, …
Mass
spectrometry
Conclusions
222Rn/226Ra
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in water - STRAW
222Rn
extraction from 350 liters
222Rn and 226Ra measurements possible
222Rn
detection limit: ~0.1 mBq/m3
Production rate: 3100 m3/h
226Ra detection limit:
~0.8 mBq/m
222Rn ≤0.5 Bq/m3 (STP)
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
3. Radon detection
222Rn
Introduction
Germanium
spectroscopy
Radon detection
emanation and diffusion
Blanks:
20 l  50 Bq
80 l  80 Bq
Absolute sensitivity
~100 Bq [50 atoms]
Mass
spectrometry
Conclusions
Sensitivity ~ 10-13 cm2/s
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
3. Radon detection
BOREXINO nylon foil
1 ppt U required
(~12 Bq/kg for 226Ra)
Ddry = 2x10-12 cm2/s (ddry= 7 m)
Dwet = 1x10-9 cm2/s (dwet = 270 m)
Introduction
Germanium
spectroscopy
Adry= Asf + 0.14  Abulk
Awet= Asf +Abulk
Radon detection
Separation of the bulk
and surface 226Ra conc.
was possible through
222Rn emanation
Mass
spectrometry
Conclusions
Very sensitive technique:
(CRa ~ 10 Bq/kg)
Bx IV foil:
bulk ≤ 15 Bq/kg
surface ≤ 0.8 Bq/m2
total = (16  4) Bq/kg (1.2 ppt U eqiv.)
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
3. Radon detection
Online 222Rn monitoring: electrostatic chamber (J. Kiko)
Introduction
Germanium
spectroscopy
Radon detection
Mass
spectrometry
Conclusions
• 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
222Rn
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Introduction
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Germanium
spectroscopy
Radon detection
Mass
spectrometry
Conclusions
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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
250 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)
Etching: 1% H2SO4 + 3% H2O2 Electropolishing: 85 % H3PO4 + 5 % 1-butanol
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
4. Mass spectrometry
Noble gas mass spectrometer
VG 3600
magnetic sector field
spectrometer.
Introduction
Germanium
spectroscopy
Used to investigate
noble gases in the
terrestial and extraterrestial samples.
Radon detection
Mass
spectrometry
Adopted to test the
nitrogen purity and
purification methods.
Conclusions
Detection limits: Ar: 10-9 cm3
Kr: 10-13 cm3
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4. Mass spectrometry
Ar and Kr in nitrogen for the BOREXINO experiment (SOL)
Introduction
Requirements:
Germanium
spectroscopy
< 7 Bq/m3
39Ar: < 0.5 Bq/m3
85Kr: < 0.2 Bq/m3
222Rn:
Radon detection
Mass
spectrometry
Ar: < 0.4 ppm
Kr: < 0.1 ppt
Conclusions
8 Bq/m3
Ar: 0.01 ppm
Kr: 0.02 ppt
222Rn:
Results:
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
4. Mass spectrometry
Kr in nitrogen: purification tests
Introduction
Germanium
spectroscopy
gas
Radon detection
Mass
spectrometry
Sample
purification
Mass spectr.
liquid
N2
6.0
Conclusions
600-L dewar with
Kr-enriched liquid
nitrogen (Westfalen A.G.)
LAr
300-cm3 column
filled with adsorber
bubbler
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
5. Conclusions
Introduction
Germanium
spectroscopy
Radon detection
Mass
spectrometry
Conclusions
• Low-level
techniques
have
“natural”
application in experiments looking for rare
events.
• There is a long tradition and a lot of
experience at MPI-K in this field
(GALLEX/GNO, HDM, BOREXINO, GERDA).
• Several detectors and experimental methods
were developed allowing measurements even
at a single atoms level.
• Some of the developed/applied techniques are
world-wide most sensitive (Ge spectroscopy,
222Rn detection).
• The ”low-level sub-group” is a part of the new
division of M. Lindner.
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007
2. Germanium spectroscopy
Comparison of different detectors
Introduction
Germanium
spectroscopy
Radon detection
Mass
spectrometry
Conclusions
Slide from M. Hult
LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007