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Nitrogen and argon radiopurity

Nitrogen and argon radiopurity. Grzegorz Zuzel for TG11 MPI-K Heidelberg. Outline. 39 Ar, 42 Ar and 85 Kr - in argon - in nitrogen 222 Rn in nitrogen and argon - concentrations in different qualities

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Nitrogen and argon radiopurity

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

  2. Outline • 39Ar, 42Ar and 85Kr - in argon - in nitrogen • 222Rn in nitrogen and argon - concentrations in different qualities - emanation from the storage tanks - purification tests • Purification system for LN2/LAr (?) • Conclusions and planned activity GERDA General Meeting, Tübingen

  3. 39Ar, 42Ar and 85Kr • Q-value of 39Ar and 85Kr 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) • 42Ar is naturally low GERDA General Meeting, Tübingen

  4. 39Ar and 85Krin argon • Dead time: Assume 10 m3 active volume • 39Ar rate: 15 kHz  1.5 % Fine! • 85Kr 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 85Kr GERDA General Meeting, Tübingen

  5. 39Arin argon • 39Ar and dark matter detection (H. Simgen) GERDA General Meeting, Tübingen

  6. 39Ar, 42Ar and 85Krin argon • 39Ar 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 of ~ 1 cts/keVrec/kg/y, which limits the ability for dark matter detection • Kr present in Ar at the ppm level would give similar contribution (through 85Kr) • Contribution from 42Ar gives 410-5 events/(kgykeV) at Q andis also negligible for dark matter GERDA General Meeting, Tübingen

  7. 39Ar and 85Krin nitrogen 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 GERDA General Meeting, Tübingen

  8. Outline • 39Ar, 42Ar and 85Kr - in argon - in nitrogen • 222Rn in nitrogen and argon - concentrations in different qualities - emanation from the storage tanks - purification tests • Purification system for LN2/LAr (?) • Conclusions and planned activity GERDA General Meeting, Tübingen

  9. 222Rn 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) GERDA General Meeting, Tübingen

  10. 222Rn concentration in Ar of different qualities (Westfalen AG) Specification: 0.5  10-3 mBq/m3 gas (STP) GERDA General Meeting, Tübingen

  11. 222Rn concentration in N2 of different qualities • 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 GERDA General Meeting, Tübingen

  12. 222Rn emanation from storage tanks CRn 1µBq/m3 Ar (STP) It should be possible to have argon with low enough 222Rn concentration without purification GERDA General Meeting, Tübingen

  13. Outline • 39Ar, 42Ar and 85Kr - in argon - in nitrogen • 222Rn in nitrogen and argon - concentrations in different qualities - emanation from the storage tanks - purification tests • Purification system for LN2/LAr (?) • Conclusions and planned activity GERDA General Meeting, Tübingen

  14. Nitrogen purification from 222Rn Liquid nitrogen purification plant works at GS for Borexino 222Rn in N2 before purif. ~50 μBq/m3 222Rn in N2 after purif. < 0.3 μBq/m3 Red. factor: > 100 Ads. mass: ~2 kg GERDA General Meeting, Tübingen

  15. Argon purification from 222Rn MoREx: Mobile Radon Extraction Unit 222Rn in Ar before purif. ~200 μBq/m3 222Rn in Ar after purif. < 0.5 μBq/m3 Red. factor: > 400 Ads. mass: ~0.15 kg GERDA General Meeting, Tübingen

  16. Ar purification from 222Rn Purification in gas phase Purification in liquid phase GERDA General Meeting, Tübingen

  17. LN2/LAr purification from 222Rn • It is possible to effectively remove radon from argon / nitrogen • Removal of 222Rn from liquid phase is somewhat less effective than from gas phase GERDA General Meeting, Tübingen

  18. Outline • 39Ar, 42Ar and 85Kr - in argon - in nitrogen • 222Rn in nitrogen and argon - concentrations in different qualities - emanation from the storage tanks - purification tests • Purification system for LN2/LAr (?) • Conclusions and planned activity GERDA General Meeting, Tübingen

  19. Purification system for LN2/LAr (?) 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 LN2 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) GERDA General Meeting, Tübingen

  20. Purification system for LAr GERDA General Meeting, Tübingen

  21. Conclusions • LN2 allows investigation of 02 (and dark matter) • 39Ar limits ability to detect dark matter if LAr is used • It is possible to buy „222Rn-free“ LN2 (proven in frame of Borexino) • 222Rn content in fresh argon is higher than in nitrogen of similar quality • It should be also possible to have „222Rn-free“ LAr without purification – still to be confirmed • 222Rn removal from argon as effective as from nitrogen • From the radiopurity point of view for GERDA 02 experiment LAr and LN2 can be used GERDA General Meeting, Tübingen

  22. Planned activity • Measure 222Rn content in argon after long storage in the tank of known emanation • 85Kr/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 GERDA General Meeting, Tübingen

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