GERDA General Meeting, Tübingen, 9.-11. November 2005 Nitrogen and argon radiopurity Grzegorz Zuzel for TG11 MPI-K Heidelberg MPI-K Heidelberg

GERDA General Meeting, GERDA General Meeting,

Tübingen, 9.-11. November 2005Tübingen, 9.-11. November 2005

Nitrogen and argon radiopurityNitrogen and argon radiopurity

Grzegorz ZuzelGrzegorz Zuzelfor TG11for TG11

MPI-K HeidelbergMPI-K Heidelberg

Grzegorz ZuzelGrzegorz Zuzel GERDA General Meeting, TübingenGERDA General Meeting, Tübingen 09.-11. Nov. 200509.-11. Nov. 2005

3939Ar, Ar, 4242Ar and Ar and 8585KrKr - in argon - in nitrogen

222222Rn in nitrogen and argon Rn in nitrogen and argon - concentrations in different qualities- concentrations in different qualities - emanation from the storage tanks- emanation from the storage tanks - purification tests- purification tests

Purification system for LNPurification system for LN22/LAr (?)/LAr (?) Conclusions and planned activityConclusions and planned activity

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3939Ar, Ar, 4242Ar and Ar and 8585KrKr

Q-value of Q-value of 3939Ar and Ar and 8585Kr below 700 keV – relevant in case Kr below 700 keV – relevant in case of dark matter detectionof dark matter detection

Dead-time could be a problem when Ar scintillation is Dead-time could be a problem when Ar scintillation is used (slow decay time: ~ 1used (slow decay time: ~ 1µµs)s)

4242Ar is naturally lowAr is naturally low

Decay modeDecay mode SourceSource Concentration (STP)Concentration (STP)

222222RnRnTT1/21/2 = 3.8 d = 3.8 d

, , , , Primordial Primordial 238238UU 1 - ?00 Bq/m1 - ?00 Bq/m33 air air

8585KrKrTT1/21/2 = 10.8 y = 10.8 y

(687 keV) , (687 keV) , 235235U fission U fission

(nuclear fuel reprocessing plants)(nuclear fuel reprocessing plants)

1.4 Bq/m1.4 Bq/m33 air air1.2 MBq/m1.2 MBq/m33 Kr Kr

3939ArArTT1/21/2 = 269 y = 269 y

(565 keV) (565 keV) CosmogenicCosmogenic 17 mBq/m17 mBq/m33 air air

1.8 Bq/m1.8 Bq/m33 Ar Ar

4242ArArTT1/21/2 = 32.9 y = 32.9 y

(600 keV)(600 keV)CosmogenicCosmogenic

0.50.5 µµBq/mBq/m33 air air50 50 µµBq/mBq/m33 Ar Ar


3939Ar and Ar and 8585KrKr in argonin argon Dead time: Dead time:

Assume 10 mAssume 10 m33 active volume active volume– 3939Ar rate: 15 kHz Ar rate: 15 kHz 1.5 % 1.5 % Fine!Fine!– 8585Kr rate not higher Kr rate not higher ≤ 0.3≤ 0.3 ppm Kr required ppm Kr required

Results from a 2.3 kg WARP test stand : Results from a 2.3 kg WARP test stand : ~ 0.6 ppm~ 0.6 ppm

Other measurement possibilities: Other measurement possibilities: - mass spectrometry of Krmass spectrometry of Kr- direct counting of direct counting of 8585KrKr


3939ArAr in argonin argon 3939Ar and dark matter detection (H. Simgen)Ar and dark matter detection (H. Simgen)


3939Ar, Ar, 4242Ar and Ar and 8585KrKr in argonin argon 3939Ar gives a significant increase of background in the Ar gives a significant increase of background in the

low energy regionlow energy region Ar scintillation used as a veto helps, however...Ar scintillation used as a veto helps, however... background index stays at the level background index stays at the level

of ~ 1 cts/keVof ~ 1 cts/keVrecrec/kg/y, which limits the ability for dark /kg/y, which limits the ability for dark matter detectionmatter detection

Kr present in Ar at the ppm level would give similar Kr present in Ar at the ppm level would give similar contribution (through contribution (through 8585Kr)Kr)

Contribution from Contribution from 4242Ar gives 4Ar gives 41010-5-5 events/(kgevents/(kgyykeV) at QkeV) at Q andand is also negligible for is also negligible for dark matter dark matter


3939Ar and Ar and 8585KrKr in nitrogenin nitrogenDescriptionDescription Ar [ppm]Ar [ppm] Kr [ppt]Kr [ppt]

MESSER RPNMESSER RPN2 2 (4.0, used in HD)(4.0, used in HD) 200200 1 6801 680

Air Liquide RPNAir Liquide RPN2 2 (4.0, used at GS)(4.0, used at GS) 1010 4040

Air Liquide HPNAir Liquide HPN22 1010 3030

Air Liquide 6.0Air Liquide 6.0 1414 1313

Linde Worms (7.0)Linde Worms (7.0) 0.0150.015 0.050.05

SOL Mantova (6.0)SOL Mantova (6.0) 0.0050.005 0.040.04

Westfalen AG Hörstel (6.0)Westfalen AG Hörstel (6.0) 0.00050.0005 0.060.06

1 ppt Kr = 1 µBq/m3 (STP)1 ppm Ar = 1.2 µBq/m3 (STP)

If LN2 is used 39Ar and 85Kr should not affect detection of dark matter





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222222Rn in nitrogen and argonRn in nitrogen and argon

According to the simulations:

222Rn in LN2/LAr at the level of ~ 0.3 mBq/m3

→ B ~ 10-4 cts/keV/kg/y

0.3 mBq/m3 liquid → 0.5 µBq/m3 gas (STP)


222222Rn concentration in Ar of different Rn concentration in Ar of different qualities (Westfalen AG)qualities (Westfalen AG)

Quality 222Rn concentration

[mBq/m3 (STP)]

Remarks

5.0 8.4 ± 0.2 At the filling time

6.0 0.38 ± 0.03 At the filling time

Specification: 0.5 10-3 mBq/m3 gas (STP)


222222Rn concentration in NRn concentration in N22 of different of different

qualitiesqualities

Quality 222Rn concentration

[mBq/m3 (STP)]

4.0 0.05 – 0.2

7.0 ~ 0.001

Conclusions:

- initial 222Rn content in nitrogen is lower than in argon of a similar class- however 222Rn decays (T1/2 =3.8 d) – emanation from the storage tank limits the final purity


222222Rn emanation from storage tanksRn emanation from storage tanksTank descriptionTank description Volume [mVolume [m33]] 222222Rn emanation rate Rn emanation rate

[mBq][mBq]

Storage tank for argon Storage tank for argon 5.0 (Westfalen)5.0 (Westfalen)

2.92.9 177 177 ± 7± 7

Storage tank for argon Storage tank for argon 6.0 (Westfalen)6.0 (Westfalen)

0.660.66 42 42 ± 2± 2

Special storage tank for Special storage tank for ultra-pure gases (Linde)ultra-pure gases (Linde)

33 2.7 2.7 ± 0.3± 0.3

CRn 1µBq/m3 Ar (STP)

It should be possible to have argon with low enough 222Rn concentration without purification


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Nitrogen purification from Nitrogen purification from 222222RnRnLiquid nitrogen purification plant works at GS for Borexino

222Rn in N2 beforepurif. ~50 μBq/m3

222Rn in N2 afterpurif. < 0.3 μBq/m3

Red. factor: > 100Ads. mass: ~2 kg


Argon purification from Argon purification from 222222RnRn

222Rn in Ar beforepurif. ~200 μBq/m3

222Rn in Ar afterpurif. < 0.5 μBq/m3

Red. factor: > 400Ads. mass: ~0.15 kg

MoREx: Mobile Radon Extraction Unit


Ar purification from Ar purification from 222222RnRn

Init. CRn [mBq/m3]

Final CRn [mBq/m3]

Red. factor

R

R/MMAdsAds

[1/kg][1/kg]0.20 ± 0.02 < 0.0005 (90% CL)< 0.0005 (90% CL) > 400> 400 > 2700> 2700

Purification in gas phase

Purification in liquid phase

Init. CRn [mBq/m3]

Final CRn [mBq/m3]

Red. factor

R

R/MMAdsAds

[1/kg][1/kg]5.4 ± 0.1 0.60 ± 0.02 99 300300

0.10 ± 0.01 0.006 ± 0.001 1717 570570

Average:Average: 1313 ~ 400~ 400


LNLN22/LAr purification from /LAr purification from 222222RnRn

It is possible to effectively remove radon from It is possible to effectively remove radon from argon / nitrogenargon / nitrogen

Removal of Removal of 222222Rn from liquid phase is Rn from liquid phase is somewhat less effective than from gas phase somewhat less effective than from gas phase


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Purification system for LNPurification system for LN22/LAr (?)/LAr (?)

Having clean storage tanks we do not need a Having clean storage tanks we do not need a purification system, but it has several advantages:purification system, but it has several advantages:

Operational conditions for the cryo-plant are more Operational conditions for the cryo-plant are more relaxed (safety, shorter “access” time)relaxed (safety, shorter “access” time)

The same system can be used for LNThe same system can be used for LN22 and LAr and LAr

purificationpurification We know how to build such a plant (Borexino plant)We know how to build such a plant (Borexino plant) Optimal column size ~200 g (LArGe) / ~1 kg Optimal column size ~200 g (LArGe) / ~1 kg

(GERDA) of CarboAct (need some further tests)(GERDA) of CarboAct (need some further tests)


Purification system for LArPurification system for LAr


ConclusionsConclusions LNLN22 allows investigation of 0 allows investigation of 022 (and dark matter) (and dark matter) 3939Ar limits ability to detect dark matter if LAr is usedAr limits ability to detect dark matter if LAr is used It is possible to buy „It is possible to buy „222222Rn-free“ LNRn-free“ LN22 (proven in frame (proven in frame

of Borexino)of Borexino) 222222Rn content in fresh argon is higher than in Rn content in fresh argon is higher than in

nitrogen of similar qualitynitrogen of similar quality It should be also possible to have „It should be also possible to have „222222Rn-free“ LAr Rn-free“ LAr

without purification – still to be confirmedwithout purification – still to be confirmed 222222Rn removal from argon as effective as from Rn removal from argon as effective as from

nitrogennitrogen From the radiopurity point of view for GERDA 0From the radiopurity point of view for GERDA 022

experiment LAr and LNexperiment LAr and LN22 can be used can be used


Planned activityPlanned activity

Measure Measure 222222Rn content in argon after long Rn content in argon after long storage in the tank of known emanationstorage in the tank of known emanation

8585Kr/Kr measurement in argonKr/Kr measurement in argon Test of a purification system for LArGe Test of a purification system for LArGe

(design for GERDA)(design for GERDA) Full supply chain test of ultra-pure nitrogen Full supply chain test of ultra-pure nitrogen

for Borexino – results interesting also for for Borexino – results interesting also for GERDAGERDA

Documents

GERDA General Meeting, Tübingen, 9.-11. November 2005 Nitrogen and argon radiopurity Grzegorz Zuzel for TG11 MPI-K Heidelberg MPI-K Heidelberg