introducing improved detection and techniques into non...

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Introducing Improved Detection Systems and Techniques into Non Destructive Assay (NDA) Programs

Graham V. Walford1,2), Debbie B. Browning2), John E. Patterson2), Laurence F. Miller1),

Sean J. Branney3), David W. Roberts3), Raymond K. Maynard3), John N. Dewes3), John E. Gunning4)

1. University of Tennessee 2. Strata-G, LLC 3. Savannah River National Laboratory4. Oak Ridge National Laboratory

Savannah River National Laboratory

David W Roberts

Sean Branney

Raymond K Maynard

John H. Dewes

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Graham V. Walford Laurence F. Miller

University of Tennessee

Jeffery A. Chapman John E. Gunning

Oak Ridge National Laboratory

NDA Targets

• NDA technologies are directed towards assessment of Special Nuclear Materials (SNM).

• SNM comprises quantification of Pu and U bearing compounds in various forms and enrichments

• The SNM is often in difficult to locate geometries within machines or other objects.

• Variability in deposit type, condition and geometric disposition are major contributors to total measurement uncertainty.

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Standards

• US DOE 414.1D

• DOE/PPPO/03‐235&D1 ‐ Quality System for Non Destructive Assay Characterization (QSNDA)

• Responding QA document of Contractor

• This Drives Subsequent Gamma and Neutron NDA

Measurement Guidance and Control

• Laboratory and Field characterization follows guidelines and controls developed over a number of years

• Detection is typically through gamma and neutron emission using techniques that have become refined.

• These techniques can be both controlling (absolutely essential) but can be restrictive in the implementation of newer detector systems or techniques.

• Controls also exist because of recognition of both the radiation based and the chemical based chemical hazards involved with SNM compounds

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Understanding the Problem

• Technical: – Better measurement – newer or optimal detection use –– minimized uncertainty –– Less risk –– optimal throughput

• Commercial: – Competitive playing field – Recognize vendor investment – Facility investment and risk

Understanding the problem ‐ The User:

• The NDA technicians and engineers must follow rigorous procedure and control to make known measurements in difficult conditions. For example in one facility:

• Detector Acceptance

• Detector Calibration

• Data and flow control

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Understanding the Problem ‐ The Manufacturer:

• Detector Makers:– Portability– Detector focus at the equipment– Restrictive application/market– Flexibility?

• Therefore:– Introducing new geometries can be difficult particularly with modeling considerations to understand

– We can build in flexibility in mind set and small changes into the controls that maintain integrity but allow other detector approaches to be examined

Two Example Detector Systems to Examine

• HMS‐4 Measurement Software/System

• HPGe Detectors

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Use of HPGe Detector :• Canberra ISOCS and Ortec IsoCart examples

• HPGe crystals are limited by the laws of physics and competitors largely make similar devices – they might argue that

• They are expensive

• Differences may fall between software and applications development

• Differences can be made in use of collimation. So look at use of parallel plate geometry. It does not solve all problems and like everything else is application specific

• This could be complex with MCNP. Using also “Peak Analysis” based upon Generalized Geometry Holdup becomes “doable” without complex collimator modeling

• Parallel plates can be MCNP modeled just takes time – set optimal geometries based upon applications

NDA Data Flow – Primary HPGe Detector Operations(For Detectors for ISOCS and “Peak Analysis”)

Confirmationof Calibration

Re Verification of Calibration

Newor

Repair

Laboratory

Field

Maintenance and

Check

Detector Acceptance

Test

To Repair by Vendor

To Repair by Vendor

Calibration(“Peak

Analysis”)

Background Checks

ISOCS

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Quality Assurance Measurements Being Made with 1.94% Enriched Source

Outline Diagram Showing Measurement of ISOCS Detector Spatial Performance with 10.892 gm U235 Source

Ge Detector

Lead Shielding Rings

Detector Axis

Source

Source‐Detector Solid Angle

Source‐Detector Distances Measured from This Location

2.0”

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Paddle Check Source Holder

Plan View

Slot for Paddle Source

Detector End Cap

Polyethylene Holder

Hole bored to allow source

direct detector view

Holder Cross

sectionSide View

Source Paddle

Detector and shield assembly

meltdown

Figure 5.4a: Variation of ISOCS response to a Point U235 (185.8 keV) Source Moved Perpendicular to the Source detector Axis at 12.0", 24.0" and 36.0" Distances

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Distance Moved (cm)

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d a

t 1

2.0

"

12.0"

24.0"

36.0"

Source

12,12,12

24,24,2436,36,36

Detector

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Figure 5.4b: Normalized Spatial Resolution for a Point Source Moved at 12.0" 24" and 36" source detector Axix for a Point Source U235 Source (185keV)

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12.0" 24.0" 36.0" Location of SRM and CRM Source at 12,12,12 location and 24,24,24, location. 36,36,36 location also shown for interest

Understanding Variance in Detection Efficiency

Axial varianceSmall Source: ε proportional to 1/d2

dRadial Variance

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Functional Diagram of an HPGe ISOCS Detector System

Non uniform attenuating body not necessarily radioactive

Non uniform distributed source

CrystalColl

Scan detector

Rotate drum if necessary

Diagram Showing Crate Measurement Geometry for ISOCS

3.0 ft

4.0 ft

7.0 ft

4.0 ft

Note: Red Locations Denote Location of WRM 3 Successive Locations For Measurement

Crate Top View Crate Side View

ISOCS

T7T8

T4

T6

T3

T5

T2T1

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Functional Diagram of an HPGe ISOCS Detector System With Data Control and Analysis

Detector Location

Power, Signal Processing, MCA

Inspector 2000Fieldof View

Shield Dewar

Laptop/PC

Quality Assurance/

Control S505

Administration

GENIE 2000Spectra

Creation

Reporting Auto

Alarm

Geometry Composer

“Peak Analysis”

MGAULACEReporting,

Data StorageResult

Bracketing the Field Measurement

Background and Source

Check

Collection of Object/Item

Spectra

Background and Source

Check

Blind Test Source Check

“Noise” Analysis

S505 Software

Procedure FBP-GVW-003

Use

NDA TrackerProgram

Procedure FBP-GVW-006

Data control

ADMIN Data CollectionProgram

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Figure 2a: NDA Summary Data Flow – Function and Decision

QC Review (scientist)

Data/Result to End

Customer

Customer Request

Energy Spectrum Series Created

Label(s) Created

Peer Review (2nd NDA Engineer)

Customer Driven


Label(s) Created

NDA Group

Created

(Items, areas, etc.,)

(Calibrations, tests, etc.,)

NDA Request

Field/lab Operations Supervisor/Data Review

1st NDA Engineer

Initial Data Analysis

Work is Done

Signature Signature ResultSignature

Signature

NDA Manager

Supervisory Review

Administrative Aide

Scan Data to

File

Pass

Order

Fail

Data/Result to NDA

Note: Signature is also a pass/fail barrier

NDA Data Flow – Function and Decision

1st NDA Engineer

Initial Data Analysis

Administrative Aide

Scan Data to

File

NDA Manager

Supervisory Review

QC Review (scientist)

Result

Signature

Data/Result to Customer or

NDA

Customer Request


Label(s) Created

Order

Signature Fail PassSignature

Peer Review (2nd NDA Engineer)

Customer Driven


Label(s) Created

NDA Group Driven

(Items, areas, etc.,)

(Calibrations, tests, etc.,)

NDA Request

Fail

Work is Done

Order

Field/lab Operations Supervisor

Data Review

Fail

Fail

Comply

Comply

Order

Order Pass

Signature

Fail Fail

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Hold Up Measurement System HMS4

• A software system where the software can reside in a laptop

• Often gets confused with an existing detector assembly

• Conventional detectors are 1” diameter and 0.5 thick – can use others –people do not because

• From the NDA point of view – physical weight – low count rate how to deal with low enrichment – clumsiness

• From the manufacturer – offers clear detector difference –package. So there fore worth working through the calibration procedure for HMS4 Generalized Geometry Holdup.

• The inspiration is the curve shown for current detector and then larger ones with Directional Radiation Monitor System

HMS4 Weight ≈ 12 lbs

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Shielded NaI(Tl) Detector Utilized for the HMS4

PMT Divider Chain

Photomultiplier tube (PMT)

NaI(Tl) Scintillator gamma ray detector

Lead shield and collimator

Note: NaI(Tl) Crystal 0.5” thickness, 1.0” diameter,

1.0”

Thin 241Am reference source

1.0”

Approximate field of view of

detector(FOV)

Pulse output

High voltage bias for PMT

235U

Natural

Depleted

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186 keV

241Am

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Sourcematerial

Collimator

Source Motion

Adjustable Distance

NaI(Tl) Scintillator and

Photomultiplier

Linear Slide

Experimental Configuration Used to Measure System Spatial Resolution. This same configuration is used with both Ge and NaI(Tl) detectors and for

spectroscopic measurement as well as Gross Counting Mode

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Distance, cm

Comparison of Spatial Resolutions for HMS4 and Walford Detector With 10.894 gm U235 "Point" source

HMS4 From Crystal Front Face to Source at 40 cm

Walford at 40 cm from collimator front face to source

Walford at 6.0 feet from collimator front face to source

HMS 4 at 40 cm

Walford at 40 cm

Walford at 6.0 feet

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Natural U

Depleted U

186 keV

1001 keV

235U Measured with NaI(Tl), LaBr3 and CZT

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Differing Enrichment 235U Sources Measured with CZT

Parallel Plate Geometry:

(Built with Alternating Pb and EPS Layers)

Sensor Element

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The Concept:Machined Expanded Polystyrene PlatesLead Foil Sheets

Lead Foils can be installed with graded foils to mitigate Pb X‐ray Generation

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Angle of Rotation

Nor

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ized

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pon

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235U (186 keV)238U (1001 keV)

235U (186 keV) response for 5.0 and 10 mm thick side shielding

238U (1001 keV) response with 10 mm side shielding

238U (1001 keV) response with 5.0 mm side shielding

Source-Detector Distance 1.0 Meter, Collimator 1.0 cm spacers, 0.5 mm plates, 10 cm by 15 cm

Creating a “Line” Field of View

FOVDetector Collimator

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Spatial Resolution and Field of View - Collimated

Source Location

Detector

Background(eliminated)

Collimator

Sweep

Old uncollimated FOV

New FOV

The Gamma Ray Directional Detector Approach

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Some Detector Field of View Options

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Distance, cm





HMS 4 at 40 cm

Walford at 40 cm

Walford at 6.0 feet

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Distance, cm

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HMS 4 at 40 cm

Walford at 40 cm

Walford at 6.0 feet

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Counts/200 sec

Distance (cm)

Rad Hunter With Narrow Collimator B Measuring 137Cs as Measured across and perpendicular to plates

Along Collimator

Across Collimator

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Better Way to Plot Data to Show Field of View?

XY

X

Y

Detector Response

HMS-4 Spatial Profile at

40 cm

35 cm

35 cm

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3.0” NaI(Tl) Spatial Profile at

40 cm With Composite Collimator

35 cm

35 cm

4.0” NaI(Tl) (Radhunter) Spatial

Profile at 40 cm With

Composite Collimator

35 cm

35 cm

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Series1

Series5

Series9

Series13

Series17

Series21

Series25

0100200300400500600700800900

1000110012001300140015001600170018001900200021002200230024002500260027002800290030003100320033003400

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

Peak Counts/200 sec

Distance 5 cm increments

Rad Hunter and Wide Collimator Spatial performance for 137Cs

3300‐3400

3200‐3300

3100‐3200

3000‐3100

2900‐3000

2800‐2900

2700‐2800

2600‐2700

2500‐2600

2400‐2500

2300‐2400

2200‐2300

2100‐2200

2000‐2100

1900‐2000

1800‐1900

1700‐1800

1600‐1700

1500‐1600

1400‐1500

1300‐1400

1200‐1300

1100‐1200

1000‐1100

900‐1000

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“Focused Plate Geometry:

(Can be plate or rectangular Pb and EPS Layers)

Sensor Element

Center of “Focal” Point

of Field of View

Steel Wall

Holdup

Fabrication of Cylindrical Collimator

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HPGe Detector

• Reduces Scatter Fraction in Energy Spectrum when observing large bodies

• Reduces continuum under lower energy peaks

• Engineering Procedures to allow such additions enables newer detector innovations

HPGe Measuring 152Eu with and without collimator

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15000

20000

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Cou

nts

Energy keV

20.11% Enriched U Source

185.72 keV

NaI(Tl)

HPGe Detector

HPGe and NaI(Tl) measuring 20% Enriched Source using parallel Plate Collimator

Summary

• Define the procedures to include “or equivalent”

• Identify where a specific and significant improvement can be made

• Enable a control experiment to demonstrate the observable difference

• Understand the cost and time to step from demonstration to approved procedure

• Speak in terms of cost/benefit/throughput to the whole process

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Thank You

introducing improved detection and techniques into non...

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