Actinides in Human Urine by Alpha Pulse Height Analysis (PHA)

Transcription

1 Actinides in Human Urine by Alpha Pulse Height Analysis (PHA) Brian K. Culligan Fellow Scientist April 20, 2012 Health Physics Society Meeting Aiken SC SRNS-L Outline Basic Principals Theory of Alpha PHA Energy & Efficiency Calibration Data Reduction, Method Detection, Decision Level and Uncertainty Analysis Quality Control Rapid Bioassay Method Interferences & Solutions Example Spectra 2 1

2 ALPHA PHA: Theory Alpha energy is converted to electronic signal (pulse) via semiconductor detector. PIPS Detector Intensity of pulse produced is proportional to the alpha energy. Mono-energetic alpha particles Energy Calibration vs. Pulse Intensity (Height) Number of pulses are proportional to the amount of isotope present. Efficiency Calibration 3 ALPHA PHA : Schematic Pre-Amp AMX/ADC (MCA) AIM Signal Pulse PIPS detector Particles Electroplated Sample 4 2

3 Energy Calibration 5 Energy Calibration 6 3

4 Efficiency Calibration Eff = cpm/dpm Weighted Mean Efficiency Calculated over the 4 Calibration isotopes. 7 Data Reduction Chemical recovery - Due to the limitations associated with any chemical process, a means of quantifying analyte losses is required. This is achieved by introducing a known concentration of a radioisotope of the analyte into the sample to be analyzed. This tracer is used to quantify the chemical losses incurred by the analyte during sample preparation. Being an isotope of the analyte, the tracer exhibits precisely the same chemical characteristics as the analyte. 8 4

5 Data Reduction Sample Activity - Once a sample has been chemically prepared and counted, the AMS software conducts a peak search within the respective ROI's; integrates or sums the number of gross counts within each ROI; and imports the background counts associated with each ROI. The activity concentration associated with each radionuclide is then calculated Act 9 Method Detection and Decision Level Minimum Detectable Amount The Minimum Detectable Amount (MDA) is the amount of a radionuclide in a sample that would be expected to go undetected 5% of the time. Decision Level The Decision Level (DL) is that activity in a sample that would have to be present for us to decide with 95% certainty that activity exists in the sample. 10 5

6 Method Detection and Decision Levels 11 Uncertainty Analysis Total Propagated Uncertainty: Efficiency, Half-Life, Recovery, Abundance, Count rate, Tracer AMS Software Calculates 2 Sigma TPU Calculated for each isotope reported Validated by GUM Workbench Analysis 12 6

7 Partial Derivatives used in TPU 13 Quality Control Primary Calibration establishes ENE and EFF NIST Certified Electroplated Standards Background measured after each calibration. Secondary QC Check (Weekly) NIST Traceable Internal Tracers/References Extensive QC Charting Capability in Software ORNL Quarterly and Double Blind Programs DOELAP Accreditation 14 7

8 VERY SMALL Needles in a Haystack! Pu/Np Am U Th 15 Rapid Bioassay Method Acidification (w/ HNO 3 ) and Tracer addition Precipitation (NH 4 OH, Calcium Phosphate) Centrifugation and Clean-Up (w/ HNO 3 and H 2 O 2 ) Dissolution and Column Extraction TEVA-TRU-Sr Triple Stacked Column Final Clean-Up (w/ HNO 3 and H 2 O 2 ) Electrodeposition Alpha Spectroscopy Data Reduction 16 8

9 Acidification, Spiking and Precipitation 17 Centrifugation 18 9

10 Clean-Up 19 Ready for Dissolution 20 10

11 Triple Stack Column Extraction Load Solution 8mL 6M HNO3 + 8mL 2M Al(NO3)3 TEVA Pu/Np Pu 236 tracer Pu/Np stripped, with 0.10M HCl-0.05M HF M rongalite Electro-deposited and counted by alpha spectroscopy. TRU U/Am Am 243 tracer U 232 tracer Am stripped with 4M HCl Electro-deposited and counted by alpha spectroscopy U stripped with Ammonium Bioxalate Electro-deposited and counted by alpha spectroscopy Sr-Res Sr Sr / Y separated Stable Sr Carrier Sr stripped with 0.05M HNO3 Mounted and counted by Gas Flow Proportional Counting Waste Rinse [Th: 9M HCl] 21 Electrodeposition & Counting 22 11

12 Interferences and Solutions Poor Actinide Separation Careful TRU/TEVA/Sr Column Extraction Careful preparation of reagents, valence control Poor Chemical Recovery / Electrodeposition Internal Tracers, Good Technique, Reagents, Procedure Cross-Contamination Dedicated Equipment and Labs for specific isotopes High Background Thorium Daughters (Recoil Suppression) Dedicated detectors for U/Th counting Use Once Glassware ROBUST cleaning 23 Plutonium-238/239 & Np

13 Americium Uranium-234/

14 Thorium-228/230/ Questions? 28 14