Analysis of 210 Pb by Accelerator Mass Spectrometry Adam Sookdeo, Supervisor: Jack Cornett M.Sc. Candidate University of Ottawa “To live a creative life, we most lose our fear of being wrong.” – Joseph Chilton Pearce

Overview Radon Generating a stable beam Quantification and measurements of 210 Pb Removal of Inferences Standard curve of 210 Pb Conclusions

Radon Image modified from Health Canada semt/radiation/radon/decay_scheme-eng.php Accessed March 2013http:// semt/radiation/radon/decay_scheme-eng.php

Measurements of 210 Pb MethodDetection limitTime ICP-MS90mBq/LMinutes CC-ICP-MS688mBq/LMinutes γ -spectrometry 440mBq1000min LSC7 mBq8-9days +in-growth period α -spectrometry 0.1-1mBq3-5days + 3-5month in- growth period Hou, X., Ross, P. Critical comparison of Radiometric and Mass Spectrometric methods for the determination of radionuclides in enviromental, biological and nuclear waste samples. Analytica Chimca: Amr, M.A., Al-Saad K.A., Helal, A.I. Ultra-trace Measurements of 210 Pb in natural occurring radioactive materials by ICP-MS. Nuclear Instruments and Methods in Physics Research A: , 2010.

The Project Can we measure a daughter product of 222 Rn, 210 Pb by Accelerator Mass Spectrometry (AMS), quantitatively?

To measure 210 Pb there were four important steps Generating a stable PbF3 - beam Quantification and measurements of 210Pb Removal of interferences Standard curve of 210 Pb

Generating negative beam: Strongest currents CompoundsIonAverage Current of 208 PbX - at 10kev (nA) a Theoretical current for 208 PbX - at 15kev (nA) b PbO +AgF 2 (F- 208 Pb-O) PbF 2 * 208 PbF PbF 2 + AgF 2 +CsF 208 PbF * The Cs sputter source was optimized for this sample a Current was collected in 30min b Assumed 15% loss in 3hrs

Theoretical calculation of count rate for 210 Pb 8.2mg of PbF 2 was packed into the targets Ionization efficiency= 208 PbF 3 - produced Initial concentration of 208 Pb atoms Ionization efficiency= 1.20x10 -3

Theoretical calculation of count rate for 210 Pb continued At terminal voltage V T = MV, the following stripping yields were measured: 208 PbF 3 -  208 Pb % 208 PbF 3 -  208 Pb % 208 PbF 3 -  208 Pb % 208 PbF 3 -  208 Pb % 208 PbF 3 -  208 Pb % 208 PbF 3 -  208 Pb % Work was preformed by Dr. Zhao To bend Pb +3 ions the V T has to be MV. The stripping yield becomes 0.76%

Theoretical calculation of count rate for 210 Pb continued Overall efficiency = ionization efficiency* transmission efficiency for Pb +3 Overall efficiency = 1.23x10 -3 * 0.76x10 -3 = 9.35x10 -5 Therefore, 1mBq or 1.01x10 6 atoms of 210 Pb would generate: Atoms measured in 3 hours= Atoms added * Overall efficiency = 10 counts

To measure 210 Pb there were four important processes Generating a stable PbF3 - beam Quantification and measurements of 210Pb Removal of interferences Standard curve of 210 Pb

Isotope dilution Image form Accessed April 2014http://en.wikipedia.org/wiki/File:Principle_of_isotope_dilution.jpg

Quantifying 210 Pb with isotope dilution Measure in Faraday cup not MCA Counting efficiency changes Abundant and variable in samples 208 Pb Measure counts in MCA Thallium-205 Not readily available 205 Pb

205 Pb isotope dilution 205 Pb Tl Zn Ba +2

Accounting for Thallium interferences 68 Zn Ba Tl +3

208 Pb isotope dilution 71pA of 208 Pb ug of 208 Pb Zero pA of 208 Pb +3 Blank

210 Pb Measurements Accumulated 210 Pb +3 spectrum 70 Zn +1 Mass to charge problem: = Pb is measured in a +3 charge state or m/z Ce +2

To measure 210 Pb there were four important processes Generating a stable PbF3 - beam Quantification and measurements of 210Pb Removal of interferences Standard curve of 210 Pb

Column Chemistry to remove interferences Load resin Convert to Bromide form Load sampleWash Elute with HCl

Removal of interferences 70 Zn Ce +2 Accumulated 210 Pb +3 spectrum

To measure 210 Pb there were four important processes Generating a stable PbF3 - beam Quantification and measurements of 210Pb Removal of interferences Standard curve of 210 Pb

208 Pb isotope dilution 70 Zn Ce +2 Packing material CsF and AgF 2 But based on isotope dilution 400mBq of 210 Pb was measured

Accounting for the efficiency differences between detectors

Measurements of Pb-210 MethodDetection limitTime ICP-MS90 mBq/LMinutes CC-ICP-MS688 mBq/LMinutes γ -spectrometry 440 mBq1000min LSC7 mBq8-9days +in-growth period α -spectrometry 0.1-1mBq3-5days + 3-5month in-growth period AMS0.04 * -1.5 mBq3-6 hours Hou, X., Ross, P. Critical comparison of Radiometric and Mass Spectrometric methods for the determination of radionuclides in enviromental, biological and nuclear waste samples. Analytica Chimca: Amr, M.A., Al-Saad K.A., Helal, A.I. Ultra-trace Measurements of 210 Pb in natural occurring radioactive materials by ICP-MS. Nuclear Instruments and Methods in Physics Research A: , * 0.3mBq detection limit with new AMS

Conclusions PbF3 - produces the strongest beam208 Pb can be used as yield tracer but: There is a difference in efficiency between atom detector and current detector Expect limit of detection to be 0.3mBq with newer AMS.

Acknowledgments Prof. Jack Cornett Prof. Liam Kieser Dr. Xiaolei Zhao Prof. Ted Litherland PDF. Chris Charles Dr. Nimal DeSilva Jack Satterly Geochronology laboratory

Thank you