IDEA Meeting, MPI-K Heidelberg, October 2004 Techniques for analysis and purification of nitrogen and argon Grzegorz Zuzel MPI-K Heidelberg

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg  Motivation of this research  Production of N 2 and Ar  Radioactive noble gases in the atmosphere  Methods of analysis  Purification of N 2 and Ar  Conclusions and planned activity Outline

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg  Ultra-pure LN 2 /LAr will be used by the GERDA experiment - Cooling medium for „naked“ Ge crystals - Cooling medium for „naked“ Ge crystals - Shield against external radiation - Shield against external radiation  Developed techniques could be applied in other low-level experiments Motivation

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Outline  Motivation of the research  Production of N 2 and Ar  Radioactive noble gases in the atmosphere  Methods of analysis  Purification of N 2 and Ar  Conclusions and planned activity

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg  N 2 and Ar are produced from air by rectification  Traces of atmospheric noble gases remain in final product  Final purity depends on individual plant and handling Production of N 2 and Ar

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Outline  Motivation of the research  Production of N 2 and Ar  Radioactive noble gases in the atmosphere  Methods of analysis  Purification of N 2 and Ar  Conclusions and planned activity

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg 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

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Requirements for GERDA  222 Rn: –MC simulations [Bernhard Schwingenheuer]: –0.3 µ Bq/m 3 N 2 (STP) = evt/(kg  y  keV)  42 Ar: –MC simulations [Stefan Schönert]: –50 µ Bq/m 3 Ar (STP) = 4  events/(kg  y  keV) 42 Ar naturally low enough

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg  Q-value of 39 Ar and 85 Kr below 700 keV  But dead-time problem when Ar scintillation is used (slow decay time:1 µ s)  Assume 10 m 3 active volume – 39 Ar rate: 17 kHzOK! – 85 Kr rate not higher  ≤ 0.3 ppm krypton required  In case of LN 2 and dark matter detection: – 39 Ar < 2.4 µBq/m 3 N 2 (0.2 ppm Ar in N 2 ) – 85 Kr < 1 µBq/m 3 N 2 (1 ppt Kr in N 2 ) Requirements for GERDA

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Outline  Motivation of the research  Production of N 2 and Ar  Radioactive noble gases in the atmosphere  Methods of analysis  Purification of N 2 and Ar  Conclusions and planned activity

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Low-level proportional counters

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg  Developed for the GALLEX experiment  Can be applied for α- and β -detection  Handmade at MPI-K (ultra-pure quartz)  Background ~1 cpd for E > 0.5 keV  Active volume of about 1 cm 3  Special filling procedure is required Low-level proportional counters

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Counter filling line

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg  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 keV threshold (bkg: 1-5 cpd) - total det. efficiency ~0.5  abs. det. limit ~100 µBq (5x Kr atoms) Sensitivities

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Measurements of 222 Rn in gases – MoREx (Mobile Radon Extraction Unit)

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Measurements of 222 Rn in gases – MoREx (Mobile Radon Extraction Unit) 222 Rn detection limit: ~0.3 μ Bq/m 3

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Ar and Kr: mass spectrometry

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg  Devoted to investigate rare gases in terrestial and extraterrestial samples  Coupled with the sample preparation and purification sections (cryo- and getter pumps)  System operated at ultra-high vacuum ( mbar)  Sample size typically ~1cm 3  Detection limits: 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 ) Ar and Kr: mass spectrometry

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Outline  Motivation of the research  Production of N 2 and Ar  Radioactive noble gases in the atmosphere  Methods of analysis  Purification of N 2 and Ar  Conclusions and planned activity

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg  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  Adsorption - successfully used for 222 Rn removal from nitrogen - a lot of experience at MPI-K Different possibilities

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg  Applied when high purities are required  Based on differences in binding energies  Strong dependence on temperature  Activated carbons and zeolites are widely used as adsorbers Gas purification by adsorption

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg 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

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Purification in the column

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Single component adsorption model  Only one parameter is involved: T Cp C -0.5  Allows to compare adsorption of different components S. Maurer, Ph.D. thesis, TU Munich (2000)  Prediction of Henry constant for adsorption on activated carbon

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Single component adsorption model Gas T C [K] P C [bar] T C ·P C -0.5 [K·bar -0.5 ] H 77 Kelvin Ar E+2 N2N2N2N E+2 Kr E+5 Rn E+14

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg  Strong binding to almost all adsorbers  Easy trapping with activated carbon at 77 K  Problem: 222 Rn emanation due to 226 Ra  Requires careful material selection  Activated carbon „CarboAct“: – 222 Rn emanation rate (0.3  0.1) mBq/kg –100 times lower than other carbons Purification of N 2 /LN 2 from 222 Rn

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg  Single component adsorption model fails for binary system N 2 /Kr  More advanced models predict strong dependence of H on the pore size of the adsorber and its internal polarity  Henry coefficient expected to be higher for pure gas phase adsorption (at T > 77 (87) K for N 2 (Ar))  Cooling: LAr (for N 2 ) or pressurized liquid gases  Pores, low polarity and adsorption from gas phase should lead to H ~1 mol/kg/Pa Purification of N 2 /LN 2 from Kr

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Henry constant and pore size

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg  Hydrophobic zeolite MFI-type: low internal polarity, pores ~5.3 Å  Hydrophobic zeolite BEA-type: a bit larger polarity than for MFI, pores ~6.6 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

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Experimental setup

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg  222 Rn removal rather easy, even from LN 2  Ar removal impossible  Kr removal requires: –Low temperature gas phase adsorption –Pore size-tuned adsorbers with low internal polarity –Low 222 Rn emanation rate Purification of N 2 – Summary

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Single component adsorption model Gas T C [K] P C [bar] T C ·P C -0.5 [K·bar -0.5 ] H 77 Kelvin Ar E+2 N2N2N2N E+2 Kr E+5 Rn E+14

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Purification of Ar  (Almost) no difference between Ar and N 2 for adsorption on activated carbon  However higher temperatures have to be considered  222 Rn removal should not be a problem  Kr removal from Ar even more challenging than for N 2 (especially for large amounts)

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg Outline  Motivation of the research  Production of N 2 and Ar  Radioactive noble gases in the atmosphere  Methods of analysis  Purification of N 2 and Ar  Conclusions and planned activity

Oct Grzegorz ZuzelIDEA Meeting, MPI-K Heidelberg  Techniques for measuring ultra-low radioactivity levels MPI-K  Nitrogen purification intensively studied - Adsorbers selection based on the adsorption theory - Adsorbers selection based on the adsorption theory - Experimental tests are ongoing - Experimental tests are ongoing - Purity tests for different supply chains are planned - Purity tests for different supply chains are planned  Argon purification seems to be a very similar problem  Purity and purification tests for Ar recently started  Although the program was slightly extended it is progressing as scheduled Conclusions and planned activity