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Actinides in Human Urine by AlphaPulse Height Analysis (PHA)

Brian K. Culligan

Fellow Scientist

April 20, 2012

Aiken SC

Health Physics Society Meeting

SRNS-L4600-2012-00040

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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

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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

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ALPHA PHA : Schematic

Particles

Electroplated Sample

PIPS detector

Pre-Amp AMX/ADC (MCA) AIM

Signal Pulse

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Energy Calibration

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Energy Calibration

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Efficiency Calibration

“Eff = cpm/DPM”

Weighted Mean Efficiency Calculated over the 4 Calibration isotopes.

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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 analyteduring sample preparation. Being an isotope of the analyte, the tracer exhibits precisely the same chemical characteristics as the analyte.

Data Reduction

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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 countswithin each ROI; and imports the background counts associated with each ROI. Theactivity concentration associated with each radionuclide is then calculated

Data Reduction

Act

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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.

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Method Detection and Decision Levels

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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

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Partial Derivatives used in TPU

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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

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VERY SMALL Needles in a Haystack!

Am

Pu/Np

U

Th

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Rapid Bioassay Method

Acidification (w/ HNO3) and Tracer addition

Precipitation (NH4OH, Calcium Phosphate)

Centrifugation and Clean-Up (w/ HNO3 and H2O2)

Dissolution and Column Extraction

TEVA-TRU-Sr Triple Stacked Column

Final Clean-Up (w/ HNO3 and H2O2)

Electrodeposition

Alpha Spectroscopy

Data Reduction

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Acidification, Spiking and Precipitation

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Centrifugation

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Clean-Up

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Ready for Dissolution

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Triple Stack Column Extraction

TEVA

TRU

Pu/Np

U/Am

Sr / Y separatedStable Sr Carrier

Sr stripped with 0.05M HNO3Mounted and counted by Gas Flow Proportional Counting

Pu/Np stripped, with 0.10M HCl-0.05M HF - 0.04M rongaliteElectro-deposited and counted by alpha spectroscopy.

U stripped with Ammonium Bioxalate

Am stripped with 4M HCl

Pu 236 tracer

U 232 tracer Electro-deposited and counted by alpha spectroscopy

Am 243 tracer

Sr-Res

Waste Rinse

Electro-deposited and counted by alpha spectroscopy

Load Solution

Sr

8mL 6M HNO3 + 8mL 2M Al(NO3)3

[Th: 9M HCl]

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Electrodeposition & Counting

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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

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Plutonium-238/239 & Np-237

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Americium-241

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Uranium-234/238

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Thorium-228/230/232

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Questions?