Use of Electret Ionization Chambers to Measure Radon in Caves

Transcription

1 Use of Electret Ionization Chambers to Measure Radon in Caves Lawrence E. Welch, Brian E. Paul, Mark D. Jones Knox College, Galesburg, Illinois, USA

2 The Study Area NE Iowa pretty much all Zone 1

3 Coldwater Cave Not a tourist cave Not an ideal laboratory Wet, muddy, high particulate burden, high CO 2 Wading = always Swimming, crawling, climbing = sometimes

4 Airborne Particulates in Coldwater Cave Focused on Formation Defocused to foreground

5 Why EIC? Why Not CRM? CRM advantage gives a temporal stream of data vs. one integrated time average value EIC advantage No electronics No moving parts other than on/off switch

6 More EIC Advantages EIC advantages Scout S L-OO Much smaller Much cheaper CRM EIC EIC Radon Scout Plus S Chamber + electret L-OO Chamber + electret Price ($) Volume (ml)

7 Why not take sequential readings with a single CRM? Much harder to do underground much more involved getting to sample site Only valid if radon activity constant during the study duration Is it?

8 How do EIC s Work? Kotrappa, P., Dempsey, J.C., Ramsey, R.W., and Stieff, L.R., A Practical E-PERM (Electret Passive Environmental Radon Monitor) System for Indoor 222 Rn Measurement. Health Physics, 58(4), pp Print.

9 Using the SPER Reader Rad-Elec, Quick Start Manual, Version 2.321i. Print.

10 Different E-PERM Configurations Not Used in this study Configuration I Configuration II Configuration III

11 Sensitivities of E-PERM Configurations V/pCi/L/day Not Used X Configuration I X Configuration II X Configuration III X George, A.C., and Bredhoff, N., Current State of the Art in Measuring Environmental Radon. Proceedings of the 2011 International Radon Symposium, pp Web. Accessed 20 July, 2016.

12 L-OO chamber modification

13 Packing in Tyvek + Kayaking Bag

14 The issue with S Chambers and Tyvek Envelopes

15 Selecting Location Within The Cave Above water level Look for drips + avoid Good airflow gif North Snake Passage Coldwater Cave

16 Experiment to Evaluate E-PERM Sensors Coldwater Cave, IA Underground river cave, 7.8 ⁰C, high CO 2. 7 locations over 2 km range Run once in December, once in June 60 Hr trial + a 36 Hr trial nested inside the 60

17 Experiment to Evaluate E-PERM Sensors Part II Each site a set of 3 EIC configurations Read initial voltage in the lab, read final voltage: A) Immediately after removal from the cave B) Again after 12-Hr equilibration in the lab

18 Calculating the uncertainty

19 Uncertainty of EIC Output December December June June A Exp B Exp A Exp B Exp Absolute Uncertainties in pci/l 60-Hr 36-Hr 60-Hr 36-Hr 7-site avg 7-site avg 7-site avg 7-site avg Config I (LT electret, S Chamber) Config II(ST electret, L-OO Chamber) Config III (LT electret, L-OO Chamber) Relative Uncertainties in % Config I (LT electret, S Chamber) 5.10% 5.29% 5.05% 5.14% Config II(ST electret, L-OO Chamber) 5.03% 5.09% 5.02% 5.05% Config III (LT electret, L-OO Chamber) 7.23% 10.75% 6.55% 8.24%

20 Radon activity, December Hr Trials 60-Hr Trials, in pci/l Spong P. Pipe Jump'n Off Platform Pothole D. Coon G. Fangs Config I (LT electret, S Chamber) Config II(ST electret, L- OO Chamber) Config III (LT electret, L-OO Chamber) ** config avg Config I + II avg config RSD (%) Config I + II RSD (%)

21 36-Hr Trials, in pci/l Radon activity, December Hr Trials Spong P. Pipe Jump'n Off Platform Pothole D. Coon G. Fangs Config I (LT electret, S Chamber) Config II(ST electret, L- OO Chamber) Config III (LT electret, L-OO Chamber) config avg Config I + II avg config RSD (%) Config I + II RSD (%)

22 60-Hr Trials, in pci/l Radon activity, June Hr Trials Spong P. Pipe Jump'n Off Platform Pothole D. Coon G. Fangs Config I (LT electret, S Chamber) Config II(ST electret, L- OO Chamber) Config III (LT electret, L-OO Chamber) config avg Config I + II avg config RSD (%) Config I + II RSD (%)

23 36-Hr Trials, in pci/l Radon activity, June Hr Trials Spong P. Pipe Jump'n Off Platform Pothole D. Coon G. Fangs Config I (LT electret, S Chamber) Config II(ST electret, L- OO Chamber) Config III (LT electret, L-OO Chamber) config avg Config I + II avg config RSD (%) Config I + II RSD (%)

24 Problems with Configuration III Least sensitive, lowest Δvoltage Most of the readings were OK, but for all 3-EIC sets at the same site, every one with an RSD greater than 10% had a very high value for Configuration III We decided to use average of Configuration I and Configuration II as the best measure for radon activity at the site

25 Config 1/Config 2 Average, December 2015

26 Config 1/Config 2 Average, June 2016

27 Configuration 1 vs. Configuration 2 Results comparable 60 Hr values had 3.7% RSD 36 Hr values had 5.5% RSD really pretty close given that there are no replicate trials 60 Hr vs. 36 Hr Short term variation pretty small here

28 Long Term Variation at the 7 sites Obviously significant seasonal variation Why? Upstream to Downstream trends different Why?

29 Which is better, Configuration I or Configuration II? Size issue would prefer using the L-OO chambers But

30 Working voltage range of electret Average initial voltage of electrets used in the study = 749V Loss of linear response =200V Working voltage range = = 549V

31 Explain cost calculation for electret Cost of a new electret =$25 Value consumed in an experimental trial: = V experimental total working voltage range cost of electret = V experimental 549V $25

32 Comparing Configurations I and II, in terms of cost and capacity Dec 2015 Dec 2015 June 2015 June Hr 36-Hr 60-Hr 36-Hr 7-site Avg 7-site Avg 7-site Avg 7-site Avg ΔV Config I (LT electret, S Chamber) ΔV Config II (ST electret, L-OO Chamber) ΔV Config III (LT electret, L-OO Chamber) Cost Config I (LT electret, S Chamber) $6.47 $3.75 $9.39 $5.55 Cost Config II (ST electret, L-OO Chamber) $11.25 $6.87 $16.42 $9.89 Cost Config III (LT electret, L-OO Chamber) $1.24 $0.68 $2.20 $1.00

33 Cost and Capacity Concerns Low volume Configuration II almost twice as expensive as Configuration I Large ΔV for 60-Hr trials using Configuration II Risk of losing linear response a major concern If radon activity was higher, would have gone off scale in June, even starting with a new E-PERM

34 Reading the Final Electret Voltage with the SPER reader Method I: In Field immediately after exit Adjust to comfortable temp in bunkhouse stove in December No temperature control in June, but mild temperatures present No humidity control Read voltages as soon as Larry gets out of his wetsuit Method II: In lab following equilibration Transport sensors to lab with climate control Low humidity, same temperature as for initial voltage reading Let sensors equilibrate 12 hours in this space Read voltages

35 Comparing Final Voltages

36 How Different Final Voltages would impact calculated radon activity Average Deviation, pci/l from Initial to Equilibrated Config I (LT electret, S Chamber) 6.9 Config II(ST electret, L-OO Chamber) 2.6 Config III (LT electret, L-OO Chamber) 29.6

37 Conclusions EPERM s work in the cave Proper in-cave protocol important Prefer small chamber, but.. Need to get a configuration that produces an intermediate delta V Too small (less than 30V), big uncertainties and too many outliers Too big (over 250V), trials are expensive and risk going into non-linear range

38 Conclusions II Really need some preliminary data to be able to gauge the proper configuration Configuration III looks bad here, but for a longer trial or cave with higher radon, it would become the best configuration Using SPER reader read in temperaturecontrolled lab after allowing sensors time to equilibrate

39 Acknowledgements Funding: Knox College Technical: Rad-Elec Access: Cave Landowners and the Coldwater Cave Project In-Cave Help: Mike Lace, Chris Beck, Ed Klausner, Elizabeth Miller, Scott Dankof, Jordan Kjone

40 The End Larry Welch Knox College Galesburg IL, USA

41 Extra Slides

42 Gamma Radiation Exposure Measurement Why needed? External ionizing radiation Kotrappa, P., and Stieff, L., The Measurement of Very High Levels of 222 Rn Concentrations using Electret Ion Chambers. Proceedings of the 1994 International Radon Symposium, pp Web. Accessed 22 July, 2016.

43 Gamma Radiation Exposure Sensor Arrow-tech Model 2 Gamma Ray Dosimeter Only have 2 units

44 Gamma Radiation Exposure Experimental Data in μr/hr Spong 21.0, Nov July 2016 Pete's Pipe 40.3, July , July 2016 Jump'n Off Point 18.0, Dec Jan 2013 Platform 16.7, Feb July 2016 Pothole Country 53.8, May , July 2016 Dead Coon 25.1, June 2016 Guardian Fangs 24.7, June 2016

45 Gamma Radiation Exposure Best Values vs. Alternative Values Best Values Spong 21.0 Pete's Pipe 40.3 Jump'n Off Point 16.9 Platform 16.7 Pothole Country 53.8 Dead Coon 25.1 Guardian Fangs 24.7 Alternative Values Dec 2015 June 2016 Spong Pete's Pipe Jump'n Off Point Platform Pothole Country Dead Coon Guardian Fangs

46 Comparison of Radon activity calculations with 2 different gamma radiation exposure background sets average deviation best - alternative December 2015 pci/l Config I (LT electret, S Chamber) 0.9 Config II(ST electret, L-OO Chamber) 1.3 Config III (LT electret, L-OO Chamber) 1.4 June 2016 Config I (LT electret, S Chamber) 0.9 Config II(ST electret, L-OO Chamber) 1.3 Config III (LT electret, L-OO Chamber) 1.4 Overall Config I (LT electret, S Chamber) 0.9 Config II(ST electret, L-OO Chamber) 1.3 Config III (LT electret, L-OO Chamber) 1.4