a correlation based pulse detection technique for gamma/neutron...

A Correlation Based Pulse Detection Technique for

Gamma/Neutron DetectorsMuhammad Faisal1), Randolph T. Schiffer1), Marek

Flaska2), Sara A. Pozzi2), David D. Wentzloff1)1) Department of Electrical Engineering and Computer Science2) Department of Nuclear Engineering and Radiological Sciences

University of Michigan, Ann Arbor, Michigan 48109, USA

Symposium on Radiation Measurements and Applications, Ann Arbor, Michigan, USA. May 24‐28, 2010

Wednesday May 26, 2010Acknowledgement: This research was funded by the National Science Foundation and the Domestic Nuclear Detection Office of the

Department of Homeland Security through the Academic Research Initiative Award # CMMI 0938909.

Motivation• Shielded radioactive materials

– Low energy radiation

– Difficult to detect

• Signal processing to detect these pulses

• Efficient online detection required (e.g. airports)

2

Shielded Materials

Detector

Real‐Time Detection

Wireless Integrated Circuits and Systems Group M. Faisal

• Analog : mostly counting pulses

• Digital : Data stored for post‐processing

• Threshold must be lowered to detect lower energy pulses

false detections

Current State‐of‐the‐Art

3

Digitizer UnitV threshold

Data Storage

A/D

A/D

A/D


PMTs

This Approach

• Data is analyzed prior to storage– Significantly less amount of data is stored

• Improve detector sensitivity• Real‐time pre‐processing

4

Pre‐processing on FPGA

Data StorageA/D

A/D

A/D


512MB Memory

FPGA• Peak extract• Timing• DSP

PMTs

Equipment

• Commercial board – 250MS/s, 14 bits, 4 channels

– Connects directly to PC (e.g. laptop)

• On‐board FPGA customizablefor pre‐processing of data

5Wireless Integrated Circuits and Systems Group M. Faisal

Real‐time detectionExtract useful information

from pulses (e.g. height, time)

Innovative Integration’s X5‐210M

• Pre‐processing in real time on an FPGA

• Measure of similarity between two signals

Normalized Cross Correlation(1/2)

6

Time


( )( )[ ] ( )[ ]

( )[ ] ( )[ ]∑∑∑

−−−

−−−=

xx u

x u

tuxtfxf

tuxtfxfuC

22( ) 11 +≤≤− uC

Signal Processing

FPGA

0.0

0.2

0.6

1.0

0.0

0.2

0.6

1.0

Time

Amplify Signal & Attenuate Noise

7

Normalized Cross Correlation(2/2)


Pulse Template 400 800

0.0

0.4

0.8

1.2

Time

Voltage

Incoming Pulses

400 800Time

C

Correlator Output

20 60 100 140

Voltage

0.0

0.4

0.8

1.2

0.0

0.4

0.8

1.2

Time


Template

Capture pulses

Bin pulse data

Average pulses in each bin

Normalize

Average 1500 pulses

Template Measured Pulses

• Template used in the correlator to recognize pulses

• Correlator building block: Multiply and Accumulate

• Available on FPGA as hardware accelerators

Hardware Implementation(1/2)


M&A∑

( ) [ ] [ ][ ] [ ]∑∑

∑ ×=

xx

x

TemplateData Incoming

TemplateData IncominguC

22

Normalize

ROM

Hardware Implementation(2/2)


( )tKD

NuC⋅

=

M&A

Data

Template

M&A

tK

N

Normalize

( )tKD

NuC⋅

=

M&A

M&AN

D

Normalize

( )tKD

NuC⋅

=

M&A

M&AN

D

Normalize

( )tKD

NuC⋅

=

M&A

M&AN

D

( )2+iC

( )iC( )1+iC

Detect tarrival

Vpk

FPGA. . .

Simulation Results (1/2)

• Pulses detected in presence of noise• E.g. A 5 keVee pulse in 5 keVee noise

11

0 5 10 15 20

0.2

0.4

0.6

0.8Co

rrelation

Energy (keVee)

Noise Level5 keVee Noise Correlation

Cth = 0.245 (3‐σ)

Pulse Correlation


1.0

Simulation Results (2/2)

• A 5 keVee pulse in presence of 5 keVee noise• Probability of detection:


2 4 6 8 10 120

0.2

0.4

0.6

0.8

1.0Prob

ability of D

etection

Energy (keVee)

Probability of Detection vs. Pulse Energy

Amplitude Threshold

CorrelatorBased

18% to 86%

Conclusion

• Proposing an FPGA‐based approach for pulse detection– Real‐time data processing

– Improved sensitivity (≈ 4x @ 5keVee)

– Reduced data storage


A Correlation Based Pulse Detection Technique for

Gamma/Neutron DetectorsMuhammad Faisal1), Randolph T. Schiffer1), Marek

Flaska2), Sara A. Pozzi2), David D. Wentzloff1)1) Department of Electrical Engineering and Computer Science2) Department of Nuclear Engineering and Radiological Sciences

University of Michigan, Ann Arbor, Michigan 48109, USA

Symposium on Radiation Measurements and Applications, Ann Arbor, Michigan, USA. May 24‐28, 2010

Wednesday May 26, 2010Acknowledgement: This research was funded by the National Science Foundation and the Domestic Nuclear Detection Office of the

Department of Homeland Security through the Academic Research Initiative Award # CMMI 0938909.

a correlation based pulse detection technique for gamma/neutron...

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