IDEA Meeting, , Paris, France New results on the Argon purification Grzegorz Zuzel Max-Planck-Institut für Kernphysik, Heidelberg

IDEA Meeting, , Paris, France Outlook  Applications of ultra-pure gases  Purification techniques  Detection of 222 Rn, 39 Ar and 85 Kr  Argon purity and purification  A new purification plant for LAr  Test of a nitrogen delivery chain  Summary

IDEA Meeting, , Paris, France Applications of ultra-pure gases (GERDA)  Tasks: - cooling of Ge crystals - shielding against external radiation  Requirements: - low boiling point - high purity  Base line: LAr, option: LN 2  LN 2 : experience from B OREXINO  LAr: better shielding properties, scintillation  Removal of radio-isotopes from (L)N 2 /(L)Ar crucial  Developed techniques can be applied in other projects (EXO, XENON, XMASS, WARP, CLEAN, …)

IDEA Meeting, , Paris, France Applications of ultra-pure gases (general)  Clean rooms ( 222 Rn – reduced atmosphere)  Clean benches  - detectors assembly  Rn-free atmosphere (nitrogen)  Blanketing  Cleaning  222 Rn emanation (cleanliness) measurements

IDEA Meeting, , Paris, France Purification techniques  Distillation: High costs and high energy consumption Big plants  Adsorption: Relatively cheap Successfully applied for 222 Rn removal (B OREXINO )  Sparging Pure gas needed anyway Boiling points are important  Buy ultra-pure gases: If commercial products fulfill requirements If purity can be kept during transportation

IDEA Meeting, , Paris, France Purification by adsorption N 2 /LN 2 + impur.N 2 /LN 2 N 2 /LN 2 + impur.N 2 /LN 2 N 2 /LN 2 + impur.N 2 /LN 2 + some impur.. Ideal situation: Real situation: VN  VN   N 2 /LN 2 + impur. V1V1 V2V2 V3V3

IDEA Meeting, , Paris, France Purification by adsorption n = H  p

IDEA Meeting, , Paris, France Possible contaminations Decay modeSourceConcentration (STP) 222 R n T 1/2 = 3.8 d , ,  Primordial 238 U1 - ?00 Bq/m 3 air 85 Kr T 1/2 = 10.8 y  (687 keV),  235 U fission (nuclear fuel reprocessing plants) 1.4 Bq/m 3 air 1.2 MBq/m 3 Kr 39 Ar T 1/2 = 269 y  (565 keV) Cosmogenic 17 mBq/m 3 air 1.8 Bq/m 3 Ar 42 Ar T 1/2 = 32.9 y  (600 keV) Cosmogenic 0.5 µBq/m 3 air 50 µBq/m 3 Ar  Q-value of 39 Ar and 85 Kr below 700 keV – relevant in case of dark matter detection  Dead time could be a problem when Ar scintillation is used (slow decay time: ~ 1µs)  42 Ar is naturally low

IDEA Meeting, , Paris, France Detection of 222 Rn, 39 Ar and 85 Kr Detection limit 0.5 µBq/m 3 (1 atom in 4 m 3 )

IDEA Meeting, , Paris, France Detection of 222 Rn, 39 Ar and 85 Kr Mass spectrometry of Ar and Kr Ar: cm 3 (1 ppb; ~1.4 nBq/m 3 for 39 Ar in N 2 ) Kr: cm 3 (0.1 ppt; ~0.1 µBq/m 3 for 85 Kr in N 2 )

IDEA Meeting, , Paris, France Nitrogen purification from Kr and Ar

IDEA Meeting, , Paris, France Nitrogen purification from Kr at -186 C

IDEA Meeting, , Paris, France 222 Rn emanation of carbon adsorbers Adsober Henry‘s constant [mol/Pa/kg] 222 Rn emanation rate [mBq/kg] Synthetic carbon CarboAct 0.21 ± ± 0.1 Carbosieve SIII (molecular sieve) 0.34 ± ± 0.2  Kr adsorption ability and 222 Rn emanation rate comparable  CarboAct is final choice (grain size, availability and prize)

IDEA Meeting, , Paris, France Argon purity studies  Argon, originally as a backup solution, became the GERDA base line  Scope of our project was extended to investigations of Argon purity and purification  Only 222 Rn seems to be relevant ( 39 Ar and 85 Kr can influence only the dead time of the detector). Allowed concentration at the level of 1  Bq/m 3 (STP, B ~ c/kg/y/keV)  Purification tests were done using CarboAct as an adsorber

IDEA Meeting, , Paris, France 222 Rn in Argon CompanyQuality 222 Rn [mBq/m 3 ] Air LiquideAr LINDE AGAr Westfalen AGAr Westfalen AGAr Westfalen AGAr Ar initially less pure than nitrogen (~0.05 mBq/m 3 ) Systematic effect due to production in air separation plants and storage (distribution)

IDEA Meeting, , Paris, France 222 Rn removal from nitrogen

IDEA Meeting, , Paris, France 222 Rn removal from nitrogen Volume [m 3 ] Initial conc. [mBq/m 3 ] Final conc. [  Bq/m 3 ] Reduction factor [1/kg]  <0.5>                10 Purity at the 1  Bq/m 3 level achieved Gas phase purification is more efficient 10 times bigger trap than 60 g-trap used in the liquid phase adsorption should be sufficient to stand 1 m 3 of LAr 150 g 60 g

IDEA Meeting, , Paris, France Ar purification plant

IDEA Meeting, , Paris, France A new adsorption column Size: 120  650 mm Volume: ~5 L CarboAct mass: 602 g 2 temperature sensors Pressure gauge Burst disc Cryo-valves Metal sealed (CF-100) Column ready for tests

IDEA Meeting, , Paris, France Test of the gas delivery path  One of the options to get ultra-pure gases is to buy them  It has to be proved that it is possible to produce them and later on deliver without loosing the purity  Crucial is cleanliness of the storage and transportation tanks ( 222 Rn emanation)

IDEA Meeting, , Paris, France 222 Rn emanation from storage tanks Tank from Quality of stored gas Vol. [m 3 ] 222 Rn activity in saturation [mBq] specific 222 Rn act. [mBq/m 3 ] Westfalen AG technical3 177 ± 659 ± 2 LINDE ± ± 0.1 Westfalen AG ± 263 ± 3 SOL ± 64.1 ± 0.4

IDEA Meeting, , Paris, France Testing SOL nitrogen Total 222 Rn budget inside tank: 65 mBq Converted in 222 Rn concentration: 6  Bq/m 3 (STP) Initial concentrations: 222 Rn: - Ar: 6 ppb Kr: 0.04 ppt

IDEA Meeting, , Paris, France Testing SOL nitrogen – initial 222 Rn

IDEA Meeting, , Paris, France Testing SOL nitrogen – 222 Rn, Ar and Kr ConditionsC Ar [ppb]C Kr [ppt]C Rn [µBq/m 3 ] V LN2 ~14.2 m 3 p ~10.5 barg 12.3    1 V LN2 ~14.2 m 3 p ~11 barg 11.1    0.6 V LN2 ~13.5 m 3 p ~11 barg 11.7    0.7 V LN2 ~6 m 3 p ~15 barg 7.4    1 V LN2 ~3 m 3 p ~15 barg 12.3    1 V LN2 ~0.8 m 3 p ~15 barg 16    5 Tank empty p ~15 barg 19    15 Is it possible to keep high purity of the gas during transportation Ar, Kr and 222 Rn do not change with the filling level of the tank The tank should not be drained! ( 222 Rn) to keep high purity of a gas

IDEA Meeting, , Paris, France Summary  Theoretical studies helped to select proper adsorbing materials and purification techniques  For a new purification system CarboAct was selected due to low 222 Rn emanation rate, good adsorption properties and reasonable prize  Project has been extended for Ar purification (gas/liquid phase)  A new adsorption column has been designed and constructed according to the results obtained for a 60-g trap  Alternative concept: no purification – instead avoiding contaminations. Full delivery chain successfully tested for nitrogen. Ar, Kr and 222 Rn can be kept under control at very low level!  Future: tests of the 5-l column