Introduction to the Toxicology application Accelerator Mass Spectrometry

Analysis of 210Pb by Accelerator Mass Spectrometry

Adam Sookdeo, Supervisor: Jack Cornett M.Sc. Candidate University of OttawaTo live a creative life, we most lose our fear of being wrong. Joseph Chilton Pearce

1Overview Radon Generating a stable beamQuantification and measurements of 210Pb Removal of Inferences Standard curve of 210PbConclusions

Radon

Image modified from Health Canada http://www.hc-sc.gc.ca/ewh-semt/radiation/radon/decay_scheme-eng.php Accessed March 20133 Measurements of 210PbMethod Detection limitTimeICP-MS90mBq/LMinutesCC-ICP-MS688mBq/LMinutes -spectrometry440mBq 1000minLSC7 mBq 8-9days +in-growth period-spectrometry0.1-1mBq3-5days + 3-5month in-growth periodHou, 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: 105-139. 2008

Amr, M.A., Al-Saad K.A., Helal, A.I. Ultra-trace Measurements of 210Pb in natural occurring radioactive materials by ICP-MS. Nuclear Instruments and Methods in Physics Research A: 237-241, 2010.

ICP-MS takes about 30sec to allow the sample to pass through, 20 secs of asparation and 20 or so sec for analysis of analyte

ICP-MS abduance sensitivity 208/210 = 10^9AMS 208/210= 10^12 potenially 10^134The Project Can we measure a daughter product of 222Rn, 210Pb by Accelerator Mass Spectrometry (AMS), quantitatively?

Here I will mention that AMS is ultra sensitive can count millions of atomsCan eliminate isobarsHas low background 5

To measure 210Pb there were four important steps

Generating negative beam: Strongest currents CompoundsIonAverage Current of 208PbX- at 10kev (nA)aTheoretical current for 208PbX- at 15kev (nA)bPbO +AgF2 (F-208Pb-O)-3436.38PbF2 *208PbF3-120128.4PbF2 + AgF2 +CsF208PbF3-175187.3*The Cs sputter source was optimized for this samplea Current was collected in 30min b Assumed 15% loss in 3hrs Theoretical calculation of count rate for 210Pb 8.2mg of PbF2 was packed into the targets

Ionization efficiency= 208PbF3- produced Initial concentration of 208Pb atoms

Ionization efficiency= 1.20x10-3

Theoretical calculation of count rate for 210Pb continued At terminal voltage VT = 1.4500 MV, the following stripping yields were measured:208PbF3- 208Pb+121.2 %208PbF3- 208Pb+213.6 %208PbF3- 208Pb+32.40 %208PbF3- 208Pb+40.62 %208PbF3- 208Pb+50.08 %208PbF3- 208Pb+60.01 %

Work was preformed by Dr. ZhaoTo bend Pb+3 ions the VT has to be 0.9600MV. The stripping yield becomes 0.76% Theoretical calculation of count rate for 210Pb continued Overall efficiency = ionization efficiency* transmission efficiency for Pb+3 Overall efficiency = 1.23x10-3 * 0.76x10-3 = 9.35x10-5

Therefore, 1mBq or 1.01x106 atoms of 210Pb would generate: Atoms measured in 3 hours= Atoms added * Overall efficiency = 10 counts

To measure 210Pb there were four important processes

Isotope dilutionImage form http://en.wikipedia.org/wiki/File:Principle_of_isotope_dilution.jpg Accessed April 2014Quantifying 210Pb with isotope dilution205Pb isotope dilution 205Pb+3 + 205Tl+3 68Zn+1137Ba+2Accounting for Thallium interferences 68Zn+1135Ba+2203Tl+3208Pb isotope dilution 210Pb MeasurementsAccumulated 210Pb+3 spectrum70Zn+1 Mass to charge problem: 70 +140 = 210 1 2 3210Pb is measured in a +3 charge state or m/z 210 3140Ce+2

To measure 210Pb there were four important processes

Column Chemistry to remove interferences

Removal of interferences70Zn+1 140Ce+2Accumulated 210Pb+3 spectrum

To measure 210Pb there were four important processes

208Pb isotope dilution 70Zn+1 140Ce+2Packing material CsF and AgF2But based on isotope dilution 400mBq of 210Pb was measuredAccounting for the efficiency differences between detectorsMeasurements of Pb-210Method Detection limitTimeICP-MS90 mBq/LMinutesCC-ICP-MS688 mBq/LMinutes-spectrometry440 mBq 1000minLSC7 mBq 8-9days +in-growth period-spectrometry0.1-1mBq3-5days + 3-5month in-growth periodAMS0.04*-1.5 mBq 3-6 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: 105-139. 2008

Amr, M.A., Al-Saad K.A., Helal, A.I. Ultra-trace Measurements of 210Pb in natural occurring radioactive materials by ICP-MS. Nuclear Instruments and Methods in Physics Research A: 237-241, 2010.

* 0.3mBq detection limit with new AMSConclusionsAcknowledgments Prof. Jack CornettProf. Liam Kieser Dr. Xiaolei Zhao Prof. Ted LitherlandPDF. Chris CharlesDr. Nimal DeSilvaJack Satterly Geochronology laboratory

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