Purification of nitrogen argon
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Purification of nitrogen (argon). Grzegorz Zuzel MPI-K Heidelberg. Outline. Motivation of this research Radioactive noble gases in the atmosphere Methods of analysis Purification of N 2 /Ar Measurements of 222 Rn content in argon gas Conclusions and planned activity. Motivation.

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Purification of nitrogen (argon)

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Purification of nitrogen argon

Purification of nitrogen (argon)

Grzegorz Zuzel

MPI-K Heidelberg

IDEA Meeting, LAL-Orsay, 14-15 April 2005


Outline

Outline

  • Motivation of this research

  • Radioactive noble gases in the atmosphere

  • Methods of analysis

  • Purification of N2/Ar

  • Measurements of 222Rn content in argon gas

  • Conclusions and planned activity

IDEA Meeting, LAL-Orsay


Motivation

Motivation

  • Ultra-pure LN2/LAr will be used in the GERDA experiment

    - Cooling medium for Ge-crystals

    - Passive shield against external radiation

    - Active shield (LAr)

  • Developed techniques could be applied in other low-level projects

IDEA Meeting, LAL-Orsay


Outline1

Outline

  • Motivation of the research

  • Radioactive noble gases in the atmosphere

  • Methods of analysis

  • Purification of N2/Ar

  • Measurements of 222Rn content in nitrogen and argon gas

  • Conclusions and planned activity

IDEA Meeting, LAL-Orsay


Radioactive noble gases in the atmosphere

Radioactive noble gases in the atmosphere

IDEA Meeting, LAL-Orsay


Outline2

Outline

  • Motivation of the research

  • Radioactive noble gases in the atmosphere

  • Methods of analysis

  • Purification of N2/Ar

  • Measurements of 222Rn content in nitrogen and argon gas

  • Conclusions and planned activity

IDEA Meeting, LAL-Orsay


Low level proportional counters

Low-level proportional counters

IDEA Meeting, LAL-Orsay


Counter filling line

Counter filling line

  • Sample purification

  • Mixing with counting

  • gas (P10)

  • Counter filling

IDEA Meeting, LAL-Orsay


Sensitivities

Sensitivities

  • 222Rn: -only α-decays detected - 50 keV threshold (bkg: 0.2 – 2 cpd)- total detection efficiency ~1.5  abs. detection limit ~30 µBq (15 atoms)

  • 39Ar and 85Kr: - β-decays detected - 0.6 keV threshold (bkg: 1 – 5 cpd) - total det. efficiency ~0.5  abs. det. limit ~100 µBq (5x10485Kr atoms)

IDEA Meeting, LAL-Orsay


Purification of nitrogen argon

Measurements of 222Rn in gases – MoREx (Mobile Radon Extraction Unit)

222Rn detection limit: ~0.3 μBq/m3

IDEA Meeting, LAL-Orsay


Ar and kr mass spectrometry

Ar and Kr: mass spectrometry

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)

IDEA Meeting, LAL-Orsay


Purification of nitrogen argon

Outline

  • Motivation of the research

  • Radioactive noble gases in the atmosphere

  • Methods of analysis

  • Purification of N2/Ar

  • Measurements of 222Rn content in nitrogen and argon gas

  • Conclusions and planned activity

IDEA Meeting, LAL-Orsay


Different possibilities

Different possibilities

  • Distillation - high costs and energy consumption

  • Sparging (e.g. with He) - boiling point for contaminants must be lower than for the gas to be purified

    - high purity carier gas needed

  • Adsorption - successfully used for 222Rn removal from nitrogen - a lot of experience at MPI-K

IDEA Meeting, LAL-Orsay


Henrys law

Henrys law

  • n = number of moles adsorbed [mol/kg]

  • p = partial pressure of adsorptive [Pa]

  • H = Henry constant [mol/(kg·Pa)]

  • H determines the retention volume:

n = H  p

VRet = HRTmAds

IDEA Meeting, LAL-Orsay


Purification in the column

Purification in the column

n = Hp

IDEA Meeting, LAL-Orsay


Purification of nitrogen argon

Adsorption models

IDEA Meeting, LAL-Orsay


Purification of n 2 ln 2 from 222 rn

Purification of N2/LN2 from 222Rn

  • Strong binding to almost all adsorbers

  • Easy trapping with activated carbon @ 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

IDEA Meeting, LAL-Orsay


Purification of n 2 ln 2 from kr

Purification of N2/LN2 from Kr

  • Advanced models needed to describe adsorption of multi-component system N2/Kr – e.g. pore size of the adsorber and its internal polarity has to be taken into account

  • Henry coefficient is expected to be higher for pure gas phase adsorption (@ T > 77 (87) K for N2 (Ar))

    - Cooling: LAr (for N2), pressurized liquid gases

    (for LAr) or gas phase cooling

  • Pores, low polarity and adsorption from gas phase should lead to H ~1 mol/kg/Pa

IDEA Meeting, LAL-Orsay


Purification of nitrogen argon

Henry constant and pore size

IDEA Meeting, LAL-Orsay


Considered adsorbers

Considered adsorbers

  • Molecular sieves, polar (Si/Al ~ 1) 5/10 Å

  • Hydrophobic zeolite MFI-type: low internal polarity (Si/Al ~ 75), pores ~6.6 Å

  • Hydrophobic zeolite BEA-type: Si/Al ~ 200, pores ~5.3 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

IDEA Meeting, LAL-Orsay


Experimental setup

Experimental setup

IDEA Meeting, LAL-Orsay


Results

Results

Synthetic carbon, CarboAct

ZEOCAT, 5.3Å, Si/Al  200

IDEA Meeting, LAL-Orsay


Results1

Results

IDEA Meeting, LAL-Orsay


Purification of n 2 summary

Purification of N2 – Summary

  • 222Rn removal rather easy, even from LN2

    • Low 222Rn emanation rate of the adsorber required

  • Ar removal impossible (no Ar reduction observed)

  • Kr removal requires:

    • Low temperature gas phase adsorption

    • Activated carbons seem to be more suitable than zeolits

    • Pore size-tuning required

IDEA Meeting, LAL-Orsay


Purification of nitrogen argon

Purification of Ar

  • (Almost) no difference between Ar and N2 for adsorption on activated carbon

  • However higher temperatures have to be considered (~100 K for pure gas phase adsorption)

  • 222Rn removal is not a problem

IDEA Meeting, LAL-Orsay


Purification of nitrogen argon

Outline

  • Motivation of the research

  • Production of N2 and Ar

  • Radioactive noble gases in the atmosphere

  • Methods of analysis

  • Purification of N2/Ar

  • Measurements of 222Rn content in nitrogen and argon gas

  • Conclusions and planned activity

IDEA Meeting, LAL-Orsay


222 rn in nitrogen and argon

222Rn in nitrogen and argon

LN2 class 4.0, usually ~ 50 m3 (STP)

of gas taken

CRn ~ 50 µBq/m3

Two measurements performed for Ar, class 4.6

IDEA Meeting, LAL-Orsay


Purification of nitrogen argon

Outline

  • Motivation of the research

  • Production of N2 and Ar

  • Radioactive noble gases in the atmosphere

  • Methods of analysis

  • Purification of N2/Ar

  • Measurements of 222Rn content in nitrogen and argon gas

  • Conclusions and planned activity

IDEA Meeting, LAL-Orsay


Conclusions and planned activity

Conclusions and planned activity

  • Nitrogen purification intensively studied

    - Adsorbers selection based on the adsorption theory

    - Experimental tests are ongoing (zeolites already tested)

    - For Kr removal from nitrogen better suitable seem to be

    activated carbons

    - Adsorption from the pure gas phase has to be studied

  • First results of purity and purification tests for Ar available

    - 222Rn removal from Ar possible

    - 222Rn concentration in argon seems to be significantly higher than in

    nitrogen of similar quality

  • Purity tests for different supply chains are planned (N2/Ar)

  • Although the program was slightly extended it is progressing as scheduled

IDEA Meeting, LAL-Orsay


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