IDEA Meeting, MPI-K Heidelberg, 21-22.October 2004 Techniques for analysis and purification of nitrogen and argon Grzegorz Zuzel MPI-K Heidelberg

IDEA Meeting, MPI-K Heidelberg, 21-22.October 2004IDEA Meeting, MPI-K Heidelberg, 21-22.October 2004

Techniques for analysis and Techniques for analysis and purification of nitrogen and argonpurification of nitrogen and argon

Grzegorz ZuzelGrzegorz ZuzelMPI-K HeidelbergMPI-K Heidelberg

Grzegorz ZuzelGrzegorz Zuzel IDEA Meeting, MPI-K HeidelbergIDEA Meeting, MPI-K Heidelberg 21-22. Oct. 200421-22. Oct. 2004

Motivation of this researchMotivation of this research Production of NProduction of N22 and Ar and Ar

Radioactive noble gases in the atmosphereRadioactive noble gases in the atmosphere Methods of analysisMethods of analysis Purification of NPurification of N22 and Ar and Ar

Conclusions and planned activityConclusions and planned activity

OutlineOutline


Ultra-pure LNUltra-pure LN22/LAr will be used by the /LAr will be used by the

GERDA experimentGERDA experiment

- Cooling medium for „naked“ Ge crystals- Cooling medium for „naked“ Ge crystals

- Shield against external radiation- Shield against external radiation

Developed techniques could be applied in Developed techniques could be applied in other low-level experimentsother low-level experiments

MotivationMotivation


OutlineOutline

Motivation of the researchMotivation of the research Production of NProduction of N22 and Ar and Ar


Conclusions Conclusions and planned activityand planned activity


NN22 and Ar are produced and Ar are produced

from air by rectificationfrom air by rectification

Traces of atmospheric Traces of atmospheric noble gases remain in noble gases remain in final productfinal product

Final purity depends on Final purity depends on individual plant and individual plant and handlinghandling

Production of NProduction of N22 and Ar and Ar


OutlineOutline





Radioactive noble gases in the Radioactive noble gases in the atmosphereatmosphere

SourceSource Concentration (STP)Concentration (STP)

222222RnRn Primordial Primordial 238238UU 10 - ?00 Bq/m10 - ?00 Bq/m33 air air

8585KrKr235235U fission (nuclear fuel U fission (nuclear fuel

reprocessing plants)reprocessing plants)1.4 Bq/m1.4 Bq/m33 air air

1.2 MBq/m1.2 MBq/m33 Kr Kr

3939ArAr CosmogenicCosmogenic 17 mBq/m17 mBq/m33 air air1.8 Bq/m1.8 Bq/m33 Ar Ar

4242ArAr CosmogenicCosmogenic0.50.5 µµBq/mBq/m33 air air50 50 µµBq/mBq/m33 Ar Ar


Requirements for GERDARequirements for GERDA

222222Rn:Rn:– MC simulations [Bernhard Schwingenheuer]:MC simulations [Bernhard Schwingenheuer]:

– 0.3 0.3 µµBq/mBq/m33 N N22 (STP) = 10 (STP) = 10-4 -4 evt/(kgevt/(kgyykeV)keV)

4242Ar:Ar:– MC simulations [Stefan Schönert]:MC simulations [Stefan Schönert]:– 50 50 µµBq/mBq/m33 Ar (STP) = 4 Ar (STP) = 41010-5-5 events/(kg events/(kgyykeV)keV)

4242Ar naturally low enoughAr naturally low enough


Q-value of Q-value of 3939Ar and Ar and 8585Kr below 700 keVKr below 700 keV But dead-time problem when Ar scintillation is used But dead-time problem when Ar scintillation is used

(slow decay time:1(slow decay time:1µµs)s)

Assume 10 mAssume 10 m33 active volume active volume– 3939Ar rate: 17 kHzAr rate: 17 kHz OK!OK!– 8585Kr rate not higher Kr rate not higher ≤ 0.3≤ 0.3 ppm krypton ppm krypton

required required

In case of LNIn case of LN22 and dark matter detection: and dark matter detection: – – 3939Ar < 2.4 µBq/mAr < 2.4 µBq/m33 N N22 (0.2 ppm Ar in N (0.2 ppm Ar in N22) ) – – 8585Kr < 1 µBq/mKr < 1 µBq/m33 N N22 (1 ppt Kr in N (1 ppt Kr in N22))

Requirements for GERDARequirements for GERDA


OutlineOutline





Low-level proportional countersLow-level proportional counters


Developed for the GALLEX experimentDeveloped for the GALLEX experiment Can be applied for Can be applied for α- α- and and ββ-detection-detection Handmade at MPI-K (ultra-pure quartz)Handmade at MPI-K (ultra-pure quartz) Background ~1 cpd for E > 0.5 keVBackground ~1 cpd for E > 0.5 keV Active volume of about 1 cmActive volume of about 1 cm33

Special filling procedure is requiredSpecial filling procedure is required

Low-level proportional countersLow-level proportional counters


Counter filling lineCounter filling line

getter-pum p

connections for d iffe rentgases (K r, A r, Xe, N , C H , ...)2 4

m ain line

h igh ly pureo ld xenon

Toepler pum p m ercurym anom eterto m ain pum p

flow m eter

carbon trap forhe lium -purifica tion

sam ple conta iner(d ism ountab le)

N aO H -trapagainst C O 2

silicageltrap

sm allcarbon

trapb ig

carbontrap

chrom osorbtrap

gasexit

exchangeablechrom atography co lum n

helium

port forproportionalcounter

topum p

gasexit

therm istor

getter-pum p

connections for d iffe rentgases (K r, A r, Xe, N , C H , ...)2 4

m ain line

h igh ly pureo ld xenon

Toepler pum p m ercurym anom eterto m ain pum p

flow m eter

carbon trap forhe lium -purifica tion

sam ple conta iner(d ism ountab le)

N aO H -trapagainst C O 2

silicageltrap

sm allcarbon

trapb ig

carbontrap

chrom osorbtrap

gasexit

exchangeablechrom atography co lum n

helium

port forproportionalcounter

topum p

gasexit

therm istor


222222Rn: Rn: -- only only α-α-decays detected decays detected

- 50 keV - 50 keV threshold (bkg: 0.2 – 2 cpd)threshold (bkg: 0.2 – 2 cpd) - total detection - total detection efficiency ~1.5efficiency ~1.5 abs. detection limit ~30 abs. detection limit ~30 µBq µBq (15 atoms)(15 atoms)

3939Ar and Ar and 8585KrKr: : - - ββ-decays detected -decays detected - 0.6 keV threshold (bkg: 1-5 cpd) - 0.6 keV threshold (bkg: 1-5 cpd)

- total det. efficiency ~0.5 - total det. efficiency ~0.5 abs. det. limit ~100 µBq abs. det. limit ~100 µBq

(5x10(5x1044 8585Kr atoms)Kr atoms)

SensitivitiesSensitivities


Measurements of Measurements of 222222Rn in gases – Rn in gases –

MoRExMoREx ( (MoMobile bile RRadon adon ExExtraction Unit)traction Unit)


Measurements of Measurements of 222222Rn in gases – Rn in gases – MoRExMoREx ( (MoMobile bile RRadon adon ExExtraction Unit)traction Unit)

222Rn detection limit: ~0.3 μBq/m3


Ar and Kr: mass spectrometryAr and Kr: mass spectrometry


Devoted to investigate rare gases in terrestial and Devoted to investigate rare gases in terrestial and extraterrestial samplesextraterrestial samples

Coupled with the sample preparation and purification Coupled with the sample preparation and purification sections (cryo- and getter pumps)sections (cryo- and getter pumps)

System operated at ultra-high vacuum (10System operated at ultra-high vacuum (10-10-10 mbar) mbar)

Sample size typically ~1cmSample size typically ~1cm33

Detection limits: Detection limits: Ar: 10Ar: 10-9-9 cm cm33 (1 ppb; ~1.4 nBq/m (1 ppb; ~1.4 nBq/m33 for for 3939Ar Ar

in Nin N22) ) Kr: 10 Kr: 10-13-13 cm cm33 (0.1 ppt; ~0.1 µBq/m (0.1 ppt; ~0.1 µBq/m33 for for 8585Kr Kr in Nin N22))

Ar and Kr: mass spectrometryAr and Kr: mass spectrometry


OutlineOutline





Distillation Distillation - high costs and energy consumption- high costs and energy consumption

Sparging (e.g. with He) Sparging (e.g. with He) - boiling point for contaminants must be - boiling point for contaminants must be

lower than lower than for the gas to be purified for the gas to be purified

AdsorptionAdsorption - successfully used for - successfully used for 222222Rn removal from nitrogen Rn removal from nitrogen - a lot of experience at MPI-K - a lot of experience at MPI-K

Different possibilitiesDifferent possibilities


Applied when high purities are requiredApplied when high purities are required

Based on differences in binding Based on differences in binding energiesenergies

Strong dependence on temperatureStrong dependence on temperature

Activated carbons and zeolites are Activated carbons and zeolites are widely used as adsorbers widely used as adsorbers

Gas purification by adsorptionGas purification by adsorption


Henrys lawHenrys law

n = number of moles adsorbed [mol/kg]n = number of moles adsorbed [mol/kg] p = partial pressure of adsorptive [Pa]p = partial pressure of adsorptive [Pa] H = Henry constant [mol/(kgH = Henry constant [mol/(kg··Pa)]Pa)]

H determines the retention volume:H determines the retention volume:

n = H p

VRet = HRTmAds


Purification in the columnPurification in the column

C0

CN

VPVRet H ()

CN

= ½

C0

ads

t

RTm

VH Re


Single component adsorption modelSingle component adsorption model

Only one parameter is involved: TOnly one parameter is involved: TCC••ppCC-0.5-0.5

Allows to compare adsorption of different Allows to compare adsorption of different componentscomponents

S. Maurer, Ph.D. thesis, TU Munich (2000)S. Maurer, Ph.D. thesis, TU Munich (2000)

Prediction of Henry constant for adsorption Prediction of Henry constant for adsorption on activated carbonon activated carbon


Single component adsorption Single component adsorption modelmodel

GasGasTTCC

[K][K]

PPCC

[bar][bar]

TTCC··PPCC-0.5-0.5

[K[K··barbar-0.5-0.5]]

H [mol/(kgH [mol/(kg··Pa)]Pa)]

@ 77 Kelvin@ 77 Kelvin

ArAr 151151 4949 21.621.6 2E+22E+2

NN22 126126 3434 21.621.6 2E+22E+2

KrKr 209209 5555 28.228.2 2E+52E+5

RnRn 377377 6363 47.647.6 1E+141E+14


Strong binding to almost all adsorbersStrong binding to almost all adsorbers Easy trapping with activated carbon at 77 KEasy trapping with activated carbon at 77 K Problem: Problem: 222222Rn emanation due to Rn emanation due to 226226RaRa Requires careful material selectionRequires careful material selection Activated carbon „CarboAct“:Activated carbon „CarboAct“:

– 222222Rn emanation rate (0.3 Rn emanation rate (0.3 0.1) mBq/kg 0.1) mBq/kg

– 100 times lower than other carbons100 times lower than other carbons

Purification of NPurification of N22/LN/LN22 from from 222222RnRn


Single component adsorption model fails for binary Single component adsorption model fails for binary system Nsystem N22/Kr/Kr

More advanced models predict strong dependence of More advanced models predict strong dependence of H on the pore size of the adsorber and its internal H on the pore size of the adsorber and its internal polaritypolarity

Henry coefficient expected to be higher for pure gas Henry coefficient expected to be higher for pure gas phase adsorption (at T > 77 (87) K for Nphase adsorption (at T > 77 (87) K for N22 (Ar)) (Ar))

Cooling: LAr (for NCooling: LAr (for N22) or pressurized liquid gases) or pressurized liquid gases Pores, low polarity and adsorption from gas phase should Pores, low polarity and adsorption from gas phase should

lead to H ~1 mol/kg/Palead to H ~1 mol/kg/Pa

Purification of NPurification of N22/LN/LN22 from Kr from Kr


Henry constant and pore sizeHenry constant and pore size

0 .01

0.1

1

10

100

1000

10000

100000

1e+06

1e+07

1e+08

1e+09

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Hen

ry c

oeffi

zien

t H

[ m

ol/(

kg*P

a)

]

Pore size b [ Angstroem ]

N itrogen

Krypton


Hydrophobic zeolite MFI-type: low internal Hydrophobic zeolite MFI-type: low internal polarity, pores ~5.3 polarity, pores ~5.3 ÅÅ

Hydrophobic zeolite BEA-type: a bit larger Hydrophobic zeolite BEA-type: a bit larger polarity than for MFI, pores ~6.6 polarity than for MFI, pores ~6.6 ÅÅ

““Carbo Act” F3/F4: low Carbo Act” F3/F4: low 222222Rn emanation Rn emanation rate, wide pore size distributionrate, wide pore size distribution

Charcoal Cloth FM 1-250, fabricCharcoal Cloth FM 1-250, fabric Activated Carbon C38/2, optimized for Activated Carbon C38/2, optimized for

solvent recoverysolvent recovery

Considered adsorbersConsidered adsorbers


Experimental setupExperimental setup

gas

liquid

600-L dewar with Kr-enriched (100 - 400 ppt)

liquid nitrogen

Mass spectr.

N2

6.0

Samplepurif ication

LN2, LAr

100/300-cm3 column filled w ith adsorber

bubbler

VRet H ()VP

C0

CN


222222Rn removal rather easy, even from LNRn removal rather easy, even from LN22

Ar removal impossibleAr removal impossible

Kr removal requires:Kr removal requires:– Low temperature gas phase adsorptionLow temperature gas phase adsorption– Pore size-tuned adsorbers with low Pore size-tuned adsorbers with low internal internal

polaritypolarity– Low Low 222222Rn emanation rateRn emanation rate

Purification of NPurification of N22 – Summary – Summary


Single component adsorption Single component adsorption modelmodel

GasGasTTCC

[K][K]

PPCC

[bar][bar]

TTCC··PPCC-0.5-0.5

[K[K··barbar-0.5-0.5]]

H [mol/(kgH [mol/(kg··Pa)]Pa)]

@ 77 Kelvin@ 77 Kelvin

ArAr 151151 4949 21.621.6 2E+22E+2

NN22 126126 3434 21.621.6 2E+22E+2

KrKr 209209 5555 28.228.2 2E+52E+5

RnRn 377377 6363 47.647.6 1E+141E+14


Purification of ArPurification of Ar

(Almost) no difference between Ar and N(Almost) no difference between Ar and N22 for for adsorption on activated carbonadsorption on activated carbon

However higher temperatures have to be However higher temperatures have to be consideredconsidered

222222Rn removal should not be a problemRn removal should not be a problem

Kr removal from Ar even more challenging Kr removal from Ar even more challenging than for Nthan for N22 (especially for large amounts) (especially for large amounts)


OutlineOutline





Techniques for measuring ultra-low radioactivity Techniques for measuring ultra-low radioactivity levels available @ MPI-Klevels available @ MPI-K

Nitrogen purification intensively studiedNitrogen purification intensively studied

- Adsorbers selection based on the adsorption theory- Adsorbers selection based on the adsorption theory

- Experimental tests are ongoing- Experimental tests are ongoing - Purity tests for different supply chains are planned- Purity tests for different supply chains are planned

Argon purification seems to be a very similar Argon purification seems to be a very similar problemproblem

Purity and purification tests for Ar recently startedPurity and purification tests for Ar recently started Although the program was slightly extended it is Although the program was slightly extended it is

progressing as scheduled progressing as scheduled


Documents

IDEA Meeting, MPI-K Heidelberg, 21-22.October 2004 Techniques for analysis and purification of nitrogen and argon Grzegorz Zuzel MPI-K Heidelberg