1. IDEA Meeting, LAL-Orsay, 14-15 April 2005 Purification of nitrogen (argon) Grzegorz Zuzel MPI-K Heidelberg

2. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay  Motivation of this research  Radioactive noble gases in the atmosphere  Methods of analysis  Purification of N 2 /Ar  Measurements of 222 Rn content in argon gas  Conclusions and planned activity Outline

3. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay  Ultra-pure LN 2 /LAr will be used in the GERDA experiment - Cooling medium for Ge-crystals - Cooling medium for Ge-crystals - Passive shield against external radiation - Passive shield against external radiation - Active shield (LAr) - Active shield (LAr)  Developed techniques could be applied in other low-level projects Motivation

4. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Outline  Motivation of the research  Radioactive noble gases in the atmosphere  Methods of analysis  Purification of N 2 /Ar  Measurements of 222 Rn content in nitrogen and argon gas  Conclusions and planned activity

5. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Radioactive noble gases in the atmosphere Source Concentration (STP) 222 Rn Primordial 238 U 10 - ?00 Bq/m 3 air 85 Kr 235 U fission (nuclear fuel reprocessing plants) 1.4 Bq/m 3 air 1.2 MBq/m 3 Kr 39 Ar Cosmogenic 17 mBq/m 3 air 1.8 Bq/m 3 Ar 42 Ar Cosmogenic 0.5 µ Bq/m 3 air 50 µ Bq/m 3 Ar

6. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Outline  Motivation of the research  Radioactive noble gases in the atmosphere  Methods of analysis  Purification of N 2 /Ar  Measurements of 222 Rn content in nitrogen and argon gas  Conclusions and planned activity

7. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Low-level proportional counters

8. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Counter filling line Sample purification Sample purification Mixing with counting Mixing with counting gas (P10) gas (P10) Counter filling Counter filling

9. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay  222 Rn: - only α- decays detected - 50 keV threshold (bkg: 0.2 – 2 cpd) - total detection efficiency ~1.5  abs. detection limit ~30 µBq (15 atoms)  39 Ar and 85 Kr : - β -decays detected - 0.6 keV threshold (bkg: 1 – 5 cpd) - total det. efficiency ~0.5  abs. det. limit ~100 µBq (5x10 4 85 Kr atoms) Sensitivities

10. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Measurements of 222 Rn in gases – MoREx (Mobile Radon Extraction Unit) 222 Rn detection limit: ~0.3 μ Bq/m 3

11. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Ar and Kr: mass spectrometry Ar: 10 -9 cm 3 (1 ppb; ~1.4 nBq/m 3 for 39 Ar in N 2 ) Kr: 10 -13 cm 3 (0.1 ppt; ~0.1 µBq/m 3 for 85 Kr in N 2 )

12. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Outline  Motivation of the research  Radioactive noble gases in the atmosphere  Methods of analysis  Purification of N 2 /Ar  Measurements of 222 Rn content in nitrogen and argon gas  Conclusions and planned activity

13. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay  Distillation - high costs and energy consumption  Sparging (e.g. with He) - boiling point for contaminants must be lower than for the gas to be purified - high purity carier gas needed - high purity carier gas needed  Adsorption - successfully used for 222 Rn removal from nitrogen - a lot of experience at MPI-K Different possibilities

14. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Henrys law  n = number of moles adsorbed [mol/kg]  p = partial pressure of adsorptive [Pa]  H = Henry constant [mol/(kg·Pa)]  H determines the retention volume: n = H  p V Ret = H  R  T  m Ads

15. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Purification in the column n = H  p

16. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Adsorption models Gas T C [K] P C [bar] T C ·P C -0.5 [K·bar -0.5 ] H [mol/(kg·Pa)] @ 77 K Pore size [Å] Ar1514921.6 2×10 2 6.8 N2N2N2N21263421.6 7 Kr2095528.2 2×10 5 7 Rn3776347.6 10 14 ~8

17. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay  Strong binding to almost all adsorbers  Easy trapping with activated carbon @ 77 K  Problem: 222 Rn emanation due to 226 Ra - Requires careful material selection - Requires careful material selection - Activated carbon „CarboAct“: - Activated carbon „CarboAct“: 222 Rn emanation rate (0.3  0.1) mBq/kg, 222 Rn emanation rate (0.3  0.1) mBq/kg, ~100 times lower than other carbons ~100 times lower than other carbons Purification of N 2 /LN 2 from 222 Rn

18. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay  Advanced models needed to describe adsorption of multi-component system N 2 /Kr – e.g. pore size of the adsorber and its internal polarity has to be taken into account  Henry coefficient is expected to be higher for pure gas phase adsorption (@ T > 77 (87) K for N 2 (Ar)) - Cooling: LAr (for N 2 ), pressurized liquid gases - Cooling: LAr (for N 2 ), pressurized liquid gases (for LAr) or gas phase cooling (for LAr) or gas phase cooling  Pores, low polarity and adsorption from gas phase should lead to H ~1 mol/kg/Pa Purification of N 2 /LN 2 from Kr

19. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Henry constant and pore size

20. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay  Molecular sieves, polar (Si/Al ~ 1) 5/10 Å  Hydrophobic zeolite MFI-type: low internal polarity (Si/Al ~ 75), pores ~6.6 Å  Hydrophobic zeolite BEA-type: Si/Al ~ 200, pores ~5.3 Å  “Carbo Act” F3/F4: low 222 Rn emanation rate, wide pore size distribution  Charcoal Cloth FM 1-250, fabric  Activated Carbon C38/2, optimized for solvent recovery Considered adsorbers

21. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Experimental setup

22. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Results ZEOCAT, 5.3Å, Si/Al  200 Synthetic carbon, CarboAct

23. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Results Adsorber description NH[mol/Pa/kg] Molecular sieve 5Å, Si/Al  1 (Carl Roth GmbH) no purification observed Molecular sieve 10Å, Si/Al  1 (Carl Roth GmbH) ≥ 1 > 2  10 -4 Zeolite, ZEOCAT, 5.3Å, Si/Al  200 (Südchemie) 4 ± 1 (6 ± 1)  10 -3 Zeolite, MFI-Type (powder), 6.6Å, Si/Al  75 (Zeochem) 1 ± 1 (6 ± 2)  10 -3 Synthetic carbon, CarboAct (CarboAct) 1 ± 1 (6 ± 2)  10 -2

24. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay  222 Rn removal rather easy, even from LN 2 –Low 222 Rn emanation rate of the adsorber required  Ar removal impossible (no Ar reduction observed)  Kr removal requires: –Low temperature gas phase adsorption –Activated carbons seem to be more suitable than zeolits –Pore size-tuning required Purification of N 2 – Summary

25. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Purification of Ar  (Almost) no difference between Ar and N 2 for adsorption on activated carbon  However higher temperatures have to be considered (~100 K for pure gas phase adsorption)  222 Rn removal is not a problem

26. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Outline  Motivation of the research  Production of N 2 and Ar  Radioactive noble gases in the atmosphere  Methods of analysis  Purification of N 2 /Ar  Measurements of 222 Rn content in nitrogen and argon gas  Conclusions and planned activity

27. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay 222 Rn in nitrogen and argon LN 2 class 4.0, usually ~ 50 m 3 (STP) of gas taken C Rn ~ 50 µBq/m 3 Two measurements performed for Ar, class 4.6 Sample No. Description C Rn in trap 1 [mBq/m 3 ] C Rn in trap 2 [mBq/m 3 ] 1 117 m 3 of gas taken 2.9 ± 0.2 – 2 141 m 3 of gas taken 0.20 ± 0.02 < 0.0005 (90% CL)

28. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay Outline  Motivation of the research  Production of N 2 and Ar  Radioactive noble gases in the atmosphere  Methods of analysis  Purification of N 2 /Ar  Measurements of 222 Rn content in nitrogen and argon gas  Conclusions and planned activity

29. 14-15 April 2005 Grzegorz ZuzelIDEA Meeting, LAL-Orsay  Nitrogen purification intensively studied - Adsorbers selection based on the adsorption theory - Adsorbers selection based on the adsorption theory - Experimental tests are ongoing (zeolites already tested) - Experimental tests are ongoing (zeolites already tested) - For Kr removal from nitrogen better suitable seem to be - For Kr removal from nitrogen better suitable seem to be activated carbons activated carbons - Adsorption from the pure gas phase has to be studied - Adsorption from the pure gas phase has to be studied  First results of purity and purification tests for Ar available - 222 Rn removal from Ar possible - 222 Rn removal from Ar possible - 222 Rn concentration in argon seems to be significantly higher than in - 222 Rn concentration in argon seems to be significantly higher than in nitrogen of similar quality nitrogen of similar quality  Purity tests for different supply chains are planned (N 2 /Ar)  Although the program was slightly extended it is progressing as scheduled Conclusions and planned activity