Transcript oct04_LN_zuzel

Techniques for analysis and
purification of nitrogen and argon
Grzegorz Zuzel
MPI-K Heidelberg
IDEA Meeting, MPI-K Heidelberg, 21-22.October 2004
Outline
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Motivation of this research
Production of N2 and Ar
Radioactive noble gases in the atmosphere
Methods of analysis
Purification of N2 and Ar
Conclusions and planned activity
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Motivation
 Ultra-pure LN2/LAr will be used by the
GERDA experiment
- Cooling medium for „naked“ Ge crystals
- Shield against external radiation
 Developed techniques could be applied in
other low-level experiments
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Outline
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Motivation of the research
Production of N2 and Ar
Radioactive noble gases in the atmosphere
Methods of analysis
Purification of N2 and Ar
Conclusions and planned activity
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Production of N2 and Ar
 N2 and Ar are produced
from air by rectification
 Traces of atmospheric
noble gases remain in
final product
 Final purity depends on
individual plant and
handling
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Outline
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Motivation of the research
Production of N2 and Ar
Radioactive noble gases in the atmosphere
Methods of analysis
Purification of N2 and Ar
Conclusions and planned activity
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Radioactive noble gases in the
atmosphere
222Rn
85Kr
39Ar
42Ar
Grzegorz Zuzel
Source
Concentration (STP)
Primordial 238U
10 - ?00 Bq/m3 air
235U
fission (nuclear fuel
reprocessing plants)
1.4 Bq/m3 air
1.2 MBq/m3 Kr
Cosmogenic
17 mBq/m3 air
1.8 Bq/m3 Ar
Cosmogenic
0.5 µBq/m3 air
50 µBq/m3 Ar
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Requirements for GERDA
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222Rn:
– MC simulations [Bernhard Schwingenheuer]:
– 0.3 µBq/m3 N2 (STP) = 10-4 evt/(kgykeV)
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42Ar:
– MC simulations [Stefan Schönert]:
– 50 µBq/m3 Ar (STP) = 410-5 events/(kgykeV)
42Ar
Grzegorz Zuzel
naturally low enough
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Requirements for GERDA
 Q-value of 39Ar and 85Kr below 700 keV
 But dead-time problem when Ar scintillation is
used (slow decay time:1µs)
 Assume 10 m3 active volume
–
–
39Ar
rate: 17 kHz
85Kr rate not higher

OK!
≤ 0.3 ppm krypton
required
 In case of LN2 and dark matter detection:
– 39Ar < 2.4 µBq/m3 N2 (0.2 ppm Ar in N2)
– 85Kr < 1 µBq/m3 N2 (1 ppt Kr in N2)
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Outline
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Motivation of the research
Production of N2 and Ar
Radioactive noble gases in the atmosphere
Methods of analysis
Purification of N2 and Ar
Conclusions and planned activity
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Low-level proportional counters
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Low-level proportional counters
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Developed for the GALLEX experiment
Can be applied for α- and β-detection
Handmade at MPI-K (ultra-pure quartz)
Background ~1 cpd for E > 0.5 keV
Active volume of about 1 cm3
Special filling procedure is required
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Counter filling line
connections for different
gases (Kr, Ar, Xe, N2, CH4, ...)
main line
getter-pump
highly pure
old xenon
port for
proportional
counter
flow meter
to
pump
helium
gas
exit
small
carbon
trap
chromosorb
trap
big
carbon
trap
Toepler pump
to main pump
Grzegorz Zuzel
mercury
manometer
gas
exit
silicagel
trap
sample container
(dismountable) carbon trap for
helium-purification
NaOH-trap
against CO2
thermistor
exchangeable
chromatography column
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Sensitivities
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222Rn:
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39Ar
- only α-decays detected
- 50 keV threshold (bkg: 0.2 – 2 cpd)
- total detection efficiency ~1.5
 abs. detection limit ~30 µBq (15 atoms)
and 85Kr: - β-decays detected
cpd)
- 0.6 keV threshold (bkg: 1-5
- total det. efficiency ~0.5
 abs. det. limit ~100 µBq
(5x104 85Kr
atoms)
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Measurements of 222Rn in gases –
MoREx (Mobile Radon Extraction Unit)
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Measurements of 222Rn in gases –
MoREx (Mobile Radon Extraction Unit)
222Rn
detection limit: ~0.3 μBq/m3
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Ar and Kr: mass spectrometry
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Ar and Kr: mass spectrometry
 Devoted to investigate rare gases in terrestial and
extraterrestial samples
 Coupled with the sample preparation and purification
sections (cryo- and getter pumps)
 System operated at ultra-high vacuum (10-10 mbar)
 Sample size typically ~1cm3
 Detection limits:
Ar: 10-9 cm3 (1 ppb; ~1.4 nBq/m3 for 39Ar in N2)
Kr: 10-13 cm3 (0.1 ppt; ~0.1 µBq/m3 for 85Kr in N2)
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Outline
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
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

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Motivation of the research
Production of N2 and Ar
Radioactive noble gases in the atmosphere
Methods of analysis
Purification of N2 and Ar
Conclusions and planned activity
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Different possibilities
 Distillation
- high costs and energy consumption
 Sparging (e.g. with He)
than
- boiling point for contaminants must be lower
for the gas to be purified
 Adsorption
- successfully used for 222Rn removal from nitrogen
- a lot of experience at MPI-K
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Gas purification by adsorption
 Applied when high purities are required
 Based on differences in binding
energies
 Strong dependence on temperature
 Activated carbons and zeolites are
widely used as adsorbers
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Henrys law
n=Hp
 n = number of moles adsorbed [mol/kg]
 p = partial pressure of adsorptive [Pa]
 H = Henry constant [mol/(kg·Pa)]
 H determines the retention volume:
VRet = HRTmAds
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Purification in the column
CN = ½ C 0
C0
H
VRe t
RTmads
CN
VRet  H ( )
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
VP
21-22. Oct. 2004
Single component adsorption model
 Prediction of Henry constant for adsorption
on activated carbon
 Only one parameter is involved: TC•pC-0.5
 Allows to compare adsorption of different
components
S. Maurer, Ph.D. thesis, TU Munich (2000)
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Single component adsorption
model
Gas
TC
[K]
PC
[bar]
TC·PC-0.5
[K·bar-0.5]
H [mol/(kg·Pa)]
@ 77 Kelvin
Ar
151
49
21.6
2E+2
N2
126
34
21.6
2E+2
Kr
209
55
28.2
2E+5
Rn
377
63
47.6
1E+14
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Purification of N2/LN2 from 222Rn
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Strong binding to almost all adsorbers
Easy trapping with activated carbon at 77 K
Problem: 222Rn emanation due to 226Ra
Requires careful material selection
Activated carbon „CarboAct“:
– 222Rn emanation rate (0.3  0.1) mBq/kg
– 100 times lower than other carbons
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Purification of N2/LN2 from Kr
 Single component adsorption model fails for binary
system N2/Kr
 More advanced models predict strong dependence of
H on the pore size of the adsorber and its internal
polarity
 Henry coefficient expected to be higher for pure gas
phase adsorption (at T > 77 (87) K for N2 (Ar))
 Cooling: LAr (for N2) or pressurized liquid gases
 Pores, low polarity and adsorption from gas phase should
lead to H ~1 mol/kg/Pa
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Henry constant and pore size
1e+09
1e+08
Henry coeffizient H [ mol/(kg*Pa) ]
1e+07
Krypton
1e+06
100000
10000
1000
100
10
Nitrogen
1
0.1
0.01
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Pore size b [ Angstroem ]
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Considered adsorbers
 Hydrophobic zeolite MFI-type: low internal
polarity, pores ~5.3 Å
 Hydrophobic zeolite BEA-type: a bit larger
polarity than for MFI, pores ~6.6 Å
 “Carbo Act” F3/F4: low 222Rn emanation
rate, wide pore size distribution
 Charcoal Cloth FM 1-250, fabric
 Activated Carbon C38/2, optimized for
solvent recovery
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Experimental setup
C0
CN
VP
VRe t  H ( )
gas
Sample
purif ication
Mass spectr.
liquid
N2
6.0
600-L dewar with
Kr-enriched (100 - 400 ppt)
liquid nitrogen
Grzegorz Zuzel
LN 2, LAr
100/300-cm3 column
filled w ith adsorber
bubbler
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Purification of N2 – Summary

222Rn
removal rather easy, even from LN2
 Ar removal impossible
 Kr removal requires:
– Low temperature gas phase adsorption
– Pore size-tuned adsorbers with low internal
polarity
– Low 222Rn emanation rate
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Single component adsorption
model
Gas
TC
[K]
PC
[bar]
TC·PC-0.5
[K·bar-0.5]
H [mol/(kg·Pa)]
@ 77 Kelvin
Ar
151
49
21.6
2E+2
N2
126
34
21.6
2E+2
Kr
209
55
28.2
2E+5
Rn
377
63
47.6
1E+14
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Purification of Ar
 (Almost) no difference between Ar and N2
for adsorption on activated carbon
 However higher temperatures have to be
considered
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222Rn
removal should not be a problem
 Kr removal from Ar even more challenging
than for N2 (especially for large amounts)
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Outline



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
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Motivation of the research
Production of N2 and Ar
Radioactive noble gases in the atmosphere
Methods of analysis
Purification of N2 and Ar
Conclusions and planned activity
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004
Conclusions and planned activity
 Techniques for measuring ultra-low radioactivity
levels available @ MPI-K
 Nitrogen purification intensively studied
- Adsorbers selection based on the adsorption theory
- Experimental tests are ongoing
- Purity tests for different supply chains are planned
 Argon purification seems to be a very similar
problem
 Purity and purification tests for Ar recently started
 Although the program was slightly extended it is
progressing as scheduled
Grzegorz Zuzel
IDEA Meeting, MPI-K Heidelberg
21-22. Oct. 2004