AN INVESTIGATION OF 

PROMPT GAMMA 

ACTIVATION ANALYSIS AND 

COMPTON IMAGING

Ben Riley

Mentor: Heather Chen-Mayer 
Overview

■ Prompt Gamma Activation Analysis

– What is Prompt Gamma Activation?

– Composition Analysis

– 3D Filament Composition

■ Compton Imaging

– Compton Scattering and Compton Camera

– Geant4 Simulation

– Image Reconstruction
Prompt Gamma Activation

■ Incident neutrons: pass through, scatter, or capture

■ Capture events excite elemental nucleus

■ Characteristic gammas emitted at de-excitation. 

■ Emission spectra characterize sample
Motivation

■ PGAA and Compton Imaging

– Bulk Composition Analysis

– Non-destructive technique

– Potential to detect impurities and corrosion: need spatial resolution
PGAA Beam Line

■ Located on NG-D

■ Polychromatic beam: average at 6 Å; Flux: 5E9 n/cm2-s

Credit: Danyal Turkoglu
■ Compare spectral intensities

■ Calculate mass ratios

■ AAXX is the net peak area, εεXX is the 

detector efficiency at the peak 

energy, σσγγ,XX is the gamma production 

cross section, and MMXX is the atomic 

mass. 

Prompt Gamma Activation Analysis 

mmHH

mmXX

=

AAHH⁄εεHH

AAXX⁄εεXX

σσγγ,XX⁄MMXX

σσγγ,HH⁄MMHH

C

C C

H

PLA Spectra
3D Printing Filament Analysis

■ Three common filaments were examined: PLA, ABS, 

and Nylon

■ Four disks for each plastic: 

– 2cm diameter

– 0.5mm-2mm thickness in 0.5mm increments

PLA Nylon ABS
Filament Properties

■ PLA

– Bioplastic: CC3HH4OO2

■ Nylon

– Overall class of polymers with different stoichiometry

■ ABS (Acrylonitrile Butadiene Styrene)

– Three part composition: CC8HH8 xx CC4HH6 yy CC3HH3NN zz

PLA Spectra

ABS Spectra Nylon Spectra
Comparison

■ Prompt gamma yield: Depth 

Dependent; Atom ratio: constant

■ Linear behavior with increased 

thickness: No self-shielding effects

■ Slope: Stoichiometric ratios

■ ABS: x:y:z=> 2:2:3

■ Nylon: Blended Filament; primarily 

nylon 6,6

ABS

PLA Atom Ratios of Various 

Materials Determined 

From PGAA

nylon

polyurethane
PGAA and Compton Imaging

■ Current PGAA

– Bulk analysis only

– Limited spatial resolution

■ Proposed For PGAA

– Use Prompt Gammas to image sample

– Utilize Compton imaging techniques

– Give spatial resolution
Compton Scattering 

■ Intermediate-High Energy Regime

■ Photon scatters off electron

■ Angle determined by

1

EE′ − 1EE

=

1−cos θθ

mmeecc2

EE θθ

EEE

EEee
Compton Camera

■ Multistage pixelated detector

– Scatters in first stage

– Absorbed in second stage

– Pixilation gives positional data

■ Generates Compton cones

– Energy deposited gives angle

1

EE′ − 1EE

=

1 − cos(θθ)

mmeecc2

– Positional data gives placement and 

orientation

■ Volumetric reconstruction from single 

scan

θθ
Simulation

■ Geant4: Monte-Carlo simulation 

for radiation transport

■ Models 5 meV neutron beam 

interacting with sample 

■ Detectors output spectra and 

Compton events

Simulated

Real

Nylon Spectra

20 cm

4 cm
Geant4 Information
Event Tracking

■ Geant4: Tracks particle events sequentially

■ Events track parent and daughter particles

■ Simulate ~1E10 Events, 3 hrs

■ High event counts allow for image reconstruction
Back Projection Reconstruction

100 Cones 1000 Cones 10000 Cones

■ Cones projected onto plane through sample

■ Conic sections plotted

■ Heat map generated
Statistical Reconstruction

■ Alternative Reconstruction Method

■ UMD School Of Medicine 

■ Computationally Faster

– 4 min vs 3 hrs

■ Smoother 

Statistical Reconstruction Back Projection

Credit: Jerimy Polf
Simulation

■ Material Filtering: Water vs Titanium

■ Spatial Resolution and Composition

Blue: H

Green: Ti

composite Disks: 0.5 mm depth

2.0 cm radius
Ti

H

Statistical Reconstruction
Conclusion

■ PGAA

– Nondestructive

– Accurately determine chemical composition

■ Compton Imaging

– Spatial Resolve Prompt Gamma emission

– Distinguish based on element

■ Together

– Complimentary techniques

– Composition and position
Special Thanks

■ Heather Chen-Mayer, Mentor

■ Danyal Turkoglu, NRC Postdoc

■ Jeremy Polf and Haijian Chen, UMD Proton Therapy Center

■ SURF Directors