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

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen  39 Ar, 42 Ar and 85 Kr - in argon - in nitrogen  222 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 LN 2 /LAr (?)  Conclusions and planned activity Outline

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen 39 Ar, 42 Ar and 85 Kr  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: ~ 1 µ s)  42 Ar is naturally low Decay mode Source Concentration (STP) 222 Rn T 1/2 = 3.8 d , ,  Primordial 238 U 1 - ?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 µ Bq/m 3 air 50 µ Bq/m 3 Ar

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen 39 Ar and 85 Kr in argon  Dead time: Assume 10 m 3 active volume Assume 10 m 3 active volume – 39 Ar rate: 15 kHz  1.5 % Fine! – 85 Kr rate not higher  ≤ 0.3 ppm Kr required Results from a 2.3 kg WARP test stand : ~ 0.6 ppm Other measurement possibilities: -mass spectrometry of Kr -direct counting of 85 Kr

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen 39 Ar in argon  39 Ar and dark matter detection (H. Simgen)

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen 39 Ar, 42 Ar and 85 Kr in argon  39 Ar gives a significant increase of background in the low energy region  Ar scintillation used as a veto helps, however... background index stays at the level background index stays at the level of ~ 1 cts/keV rec /kg/y, which limits the ability for dark matter detection of ~ 1 cts/keV rec /kg/y, which limits the ability for dark matter detection  Kr present in Ar at the ppm level would give similar contribution (through 85 Kr)  Contribution from 42 Ar gives 4  events/(kg  y  keV) at Q  and is also negligible for dark matter

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen 39 Ar and 85 Kr in nitrogen Description Ar [ppm] Kr [ppt] MESSER RPN 2 (4.0, used in HD) Air Liquide RPN 2 (4.0, used at GS) 1040 Air Liquide HPN Air Liquide Linde Worms (7.0) SOL Mantova (6.0) Westfalen AG Hörstel (6.0) ppt Kr = 1 µBq/m 3 (STP) 1 ppm Ar = 1.2 µBq/m 3 (STP) If LN 2 is used 39 Ar and 85 Kr should not affect detection of dark matter

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen  39 Ar, 42 Ar and 85 Kr - in argon - in nitrogen  222 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 LN 2 /LAr (?)  Conclusions and planned activity Outline

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen 222 Rn in nitrogen and argon According to the simulations: 222 Rn in LN 2 /LAr at the level of ~ 0.3 mBq/m 3 → B ~ cts/keV/kg/y 0.3 mBq/m 3 liquid → 0.5 µBq/m 3 gas (STP)

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen 222 Rn concentration in Ar of different qualities (Westfalen AG) Quality 222 Rn concentration [mBq/m 3 (STP)] Remarks ± 0.2At the filling time ± 0.03At the filling time Specification: 0.5  mBq/m 3 gas (STP)

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen 222 Rn concentration in N 2 of different qualities Quality 222 Rn concentration [mBq/m 3 (STP)] – ~ Conclusions: - initial 222 Rn content in nitrogen is lower than in argon of a similar class - however 222 Rn decays (T 1/2 =3.8 d) – emanation from the storage tank limits the final purity

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen 222 Rn emanation from storage tanks Tank description Volume [m 3 ] 222 Rn emanation rate [mBq] Storage tank for argon 5.0 (Westfalen) ± 7 Storage tank for argon 6.0 (Westfalen) ± 2 Special storage tank for ultra-pure gases (Linde) ± ± 0.3 C Rn  1µBq/m 3 Ar (STP) It should be possible to have argon with low enough 222 Rn concentration without purification

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen Outline  39 Ar, 42 Ar and 85 Kr - in argon - in nitrogen  222 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 LN 2 /LAr (?)  Conclusions and planned activity

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen Nitrogen purification from 222 Rn Liquid nitrogen purification plant works at GS for Borexino 222 Rn in N 2 before purif. ~50 μBq/m Rn in N 2 after purif. < 0.3 μBq/m 3 Red. factor: > 100 Ads. mass: ~2 kg

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen Argon purification from 222 Rn 222 Rn in Ar before purif. ~200 μBq/m Rn in Ar after purif. < 0.5 μBq/m 3 Red. factor: > 400 Ads. mass: ~0.15 kg MoREx: Mobile Radon Extraction Unit

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen Ar purification from 222 Rn Init. C Rn [mBq/m 3 ] Final C Rn [mBq/m 3 ] Red. factor R M Ads R/M Ads[1/kg] 0.20 ± 0.02 < (90% CL) > 400 > 2700 Purification in gas phase Purification in liquid phase Init. C Rn [mBq/m 3 ] Final C Rn [mBq/m 3 ] Red. factor R M Ads R/M Ads[1/kg] 5.4 ± ± ± ± Average: ~ 400

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen LN 2 /LAr purification from 222 Rn  It is possible to effectively remove radon from argon / nitrogen  Removal of 222 Rn from liquid phase is somewhat less effective than from gas phase

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen Outline  39 Ar, 42 Ar and 85 Kr - in argon - in nitrogen  222 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 LN 2 /LAr (?)  Conclusions and planned activity

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen Purification system for LN 2 /LAr (?) Having clean storage tanks we do not need a purification system, but it has several advantages: Having clean storage tanks we do not need a purification system, but it has several advantages:  Operational conditions for the cryo-plant are more relaxed (safety, shorter “access” time)  The same system can be used for LN 2 and LAr purification  We know how to build such a plant (Borexino plant)  Optimal column size ~200 g (LArGe) / ~1 kg (GERDA) of CarboAct (need some further tests)

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen Purification system for LAr

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen Conclusions  LN 2 allows investigation of 0 2  (and dark matter)  39 Ar limits ability to detect dark matter if LAr is used  It is possible to buy „ 222 Rn-free“ LN 2 (proven in frame of Borexino)  222 Rn content in fresh argon is higher than in nitrogen of similar quality  It should be also possible to have „ 222 Rn-free“ LAr without purification – still to be confirmed  222 Rn removal from argon as effective as from nitrogen  From the radiopurity point of view for GERDA 0 2  experiment LAr and LN 2 can be used

Nov Grzegorz ZuzelGERDA General Meeting, Tübingen Planned activity  Measure 222 Rn content in argon after long storage in the tank of known emanation  85 Kr/Kr measurement in argon  Test of a purification system for LArGe (design for GERDA)  Full supply chain test of ultra-pure nitrogen for Borexino – results interesting also for GERDA