Transuranic Air Filter Analysis Techniques - INMM · • Conservative TRU estimator model ... 6 Transuranic Air Filter Analysis Techniques S. Joseph Cope ... Novel fit of a 4. th

Transuranic Air Filter Analysis Techniques

S. Joseph Cope CNEC Fellow, PhD Student Advisor: Dr. Robert Hayes Consortium for Nonproliferation Enabling Capabilities (CNEC) Department of Nuclear Engineering North Carolina State University

2 Transuranic Air Filter Analysis Techniques S. Joseph Cope

• Scope and background • Methods and materials • Conservative TRU estimator model • Results (Kernel density estimator)

– Gaussian superposition and deconvolution – Next individual filter predictions

• Discussion and implications • Conclusions and future work

Outline


• Goal: Graded approach for rapid, defensible TRU activity estimates – Hours and days vs weeks for full radiochemistry

• Method: Field Deployable Portable Air Samplers with various single filter detection suites – Gross alpha/beta, spectroscopic, and ROI

Nuclear Assay in Radiological Emergency Response via Air Monitoring

• Gas Proportional Counter • PIPS detector (silicon) • Phoswich

• Liquid Scintillation • Radeye Handheld Probe • Portable HPGe


• Rapid, defensible, conservative method for TRU activity estimation (Master’s work)

• Graded Approach – minutes hours days – Handheld probe PIPS/Phoswich/LSC HPGe – Truck/mobile lab analysis prioritize samples of

interest for additional analysis or radiochemistry

Research Snapshot


• Go/no-go decision levels with technical basis – Cognizant to the technician and end user decision maker

• Introduce TRU check source to NORM background filter experiment – Variations in geographic region, seasonal, diurnal and

local weather conditions

Goal: Continuing to engage more students and pursue mission critical data with national security implications

Nonproliferation and Emergency Response


• A rapid, defensible, and conservative TRU activity estimate with an emergency response decision level for clearing air filter samples – Radon and thoron are known interferents to TRU

determination on air filters; concentrations are not constant over time or easily forward predicted

– Samples containing no TRU content compared to the expected value of zero activity

– Quantifies the bias of the long-lived thoron progeny to estimate the TRU activity on the filter rapidly

Scope


Naturally Occurring Radioactive Material


• Planned releases (universities, power plants, labs)

• RDDs

Anthropogenic and TRU Sources

• Detonations

• Accidents


• Diurnal and seasonal variations

Challenges to Radon Concentration

Seftelis et al. “Diurnal variation of radon progeny.” Journal of Environmental Radioactivity. 2007


• Dependency on meteorological conditions

Challenges to Radon Concentration

Seftelis et al. “Diurnal variation of radon progeny.” Journal of Environmental Radioactivity. 2007


• Grab sampling, 02 Dec 2016 – 23 Jan 2017 • Gross alpha, 2 hr counting times in 5 min increments • 23 paired experiments (46 filters total) • Outside Research Building II, NCSU Centennial Campus • Approximately 0.5 m between samplers, nominal flow

rate 29.2 ± 1.6 LPM

Materials and Methods


• F&J Specialty Products Portable Air Samplers (Model DF-AB-75L and DF-AB-40Li)

Methods and Materials

• Bladewerx SabreISC (integrated sample counter) with 47 mm solid-state ion-implanted silicon detector

• FP47M glass fiber, 47 mm circular discs from F&J Specialty Products


• 23 dual (paired) experiments considered

Time and Length of Grab Sampling

Samples of note for attribution of the 4th

Gaussian curve


• m1 estimates the radon progeny initial activity on the filter (Bq)

• m2 estimates the effective decay constant folding in all of the radon progeny (min-1) – Effective radon progeny t1/2 ~ 30 min (NCRP 1988)

• m3 estimates the TRU content on the filter (Bq) – Expected value is zero ignoring thoron contributions

Simplified Progeny Decay Equation

1 2 3( ) exp( )y t m m t m= − +


• Among the short time scale of counting (~2 hrs), the thoron contribution, when present, is relatively unchanged (t1/2 thoron ~ 10.6 hrs)

• The conservative m3 folds in the thoron activity to the long-lived TRU estimate – Thoron contribution builds up over sample duration

compared to radon which saturates within 1-2 hours – Samples known to be CLEAN (no TRU content)

Conservative TRU Estimator (m3)


• Utilizing a KDE removes error associated with incorrect binning of mean values with known uncertainty and creates a continuous distribution for statistical analysis

Kernel Density Estimator (KDE) for m3

( ) 212

1

1( )2

i

i

x

n

i i

eKDE xn

µσ

σ π

−−

=

= ∑


• Superposition of multiple Gaussian distributions – Levenberg-Marquardt fitting provides error estimate

Gaussian Fit and Deconvolution of the KDE

3 Gaussian Fit

4 Gaussian Fit


Gaussian Deconvolution of the KDE

• Previous work has attributed each Gaussian curve to a specific component of the experiment based on center and spread statistics rather than amplitude

• Novel fit of a 4th Gaussian curve to account for positively biased anomaly in the KDE 0.18 Bq.


• Histogram of upper 95% confidence level for all individual TRU activity estimates using the fitted LM uncertainty for each filter

• All upper 95% TRU estimates are greater than zero; potentially a method for strictly conservative TRU activity estimates contained in a relatively small bias (<1.5 Bq)

What is potentially a radical advance?

Two outliers omitted


• Upper 95% estimate applied individually for each filter based on LM fitting; projected screening decision level for any individual filter, above which, a TRU activity hit is considered for the sampled times and region; – Filters considered to be absent of abnormal TRU activity

• Results for TRU activity and Gaussian attributions match expectations from known physics and dispersion of radon and thoron progeny;

• The 4th fitted Gaussian accounts for longer sampling periods and trends with the radon progeny concentration – Higher thoron buildup over sampling time along with radon peaks

in the morning hours due to temperature inversions

Discussion


Emergency Response and Nonproliferation

• Rigorous uncertainty determination, even if large, allows for defensible emergency response decisions (evacuation)

• Rapid NDA screening technique to reduce the burden of throughput placed on limited radiochemistry resources – Helps to prioritize samples for analysis before arrival to the lab – Initial proliferation indicators screened quickly with quality

• Deconvolution of the KDE into Gaussians for each variability allows for hypothesis testing on individual contributions

• Discrimination of radionuclides with grossly different decay constants


• Rapid filter counting methods allow defensible estimates – Good for proliferation and emergency response screening

• Conservative 95% upper confidence level for a single filter at 0.4 Bq for seasonal and geographic interests with two locally disturbed samples omitted – Assuming a representative characterization of the spread in

radon/thoron concentrations, these results would be reproducible in similar geographical regions and times of year

• Seek to artificially introduce Pu-239 onto a filter counting experiment to simulate TRU content masked by the NORM buildup; analysis of alpha energy ROI for Pu-239

Conclusions and Future Work


Special thanks to…

Questions? See me at the poster session!

S. Joseph Cope, [email protected]

This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number(s) DE-NA0002576.

Documents

Transuranic Air Filter Analysis Techniques - INMM · • Conservative TRU estimator model ... 6 Transuranic Air Filter Analysis Techniques S. Joseph Cope ... Novel fit of a 4. th