RMD RadCam Thesis II report - du.kim

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Commissioning the RMD RadCam using

coded aperture collimator

Thesis II Final Report

Faculty of Energy Systems and Nuclear Science

University of Ontario Institute of Technology

April 17, 2015

Authors:

DuHwan Kim

Supervisors:

Dr. Anthony Waker

Dr. Gloria Orchard

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Acknowledgements I would like to express our deep appreciation to our Thesis advisors Dr. Anthony Waker and Dr.

Gloria Orchard for their patience and guidance throughout the whole semesters. Their time and

dedication has motivated and enabled me to successfully complete this project.

As well, I would like to thank those professors who encouraged me during my undergraduate

career proving me with the foundations on which continues to build our academic knowledge in

Health Physics and Radiation Science.

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Table of Contents Acknowledgements ......................................................................................................................... 2

Executive Summary ........................................................................................................................ 4

1. Introduction ............................................................................................................................. 6

2. Material and Methods .............................................................................................................. 6

2.1 Calibration ........................................................................................................................ 9

2.2 Alignment ....................................................................................................................... 10

2.3 Spatial resolution ............................................................................................................ 11

3. Analysis ................................................................................................................................. 11

3.1 Calibration ...................................................................................................................... 12

3.1.1 Calibration Verification .............................................................................................. 15

3.1.2 A comparison of pinhole and coded aperture collimator ........................................... 20

3.1.3 A comparison of coded aperture collimator in narrow vs. wide view ........................ 21

3.1.4 Absolute peak efficiency and Resolution ................................................................... 23

3.2 Alignment ....................................................................................................................... 26

3.2.1 Phase I: Acquisition of a strong source ...................................................................... 27

3.2.2 Phase II: Experiment Execution ................................................................................. 28

3.3 Spatial resolution ............................................................................................................ 29

3.3.1 Phase I: Acquisition of strong two sources ................................................................ 30

3.3.2 Phase II: Experiment Execution ................................................................................. 30

4. Conclusion ............................................................................................................................. 31

5. Appendix A: Sample Calculation .......................................................................................... 34

6. Appendix B: Experimental Protocol ...................................................................................... 37

7. Appendix C: Table of Spatial resolution ULT: 100% & LLT: 60% ..................................... 41

8. Appendix D: Table of Spatial resolution ULT: 80% & LLT: 60% ....................................... 42

9. References .............................................................................................................................. 43

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Executive Summary The RMD RadCam is as spectroscopic gamma ray imaging system which provides a

qualitative image of gamma ray producing material. In order to commission the RMD RadCam

for use at the University of Ontario Institute of Technology, three major experiments including

the energy calibration, nuclear and video alignment and spatial resolution were completed. For

those experiments, the RMD RadCam was equipped with the coded aperture collimator and the

field of view was set to wide. The six point energy calibration was executed by obtaining six

separate spectra of the Cadmium-109 (Cd-109), Cobalt-57 (Co-57), Sodium-22 (Na-22),

Cesium-137 (Cs-137), Manganese-54 (Mn-54) and Unknown (Cs-137 & Zn-65). In this

experiment, chemistry standing was used to hold each point sources 2.5 cm away from the coded

aperture because source could not attached directly to the coded aperture. Using this relationship,

the calibration curve equation of y = 2.1353x + 39.708 was obtained. This equation was used to

determine the energy corresponding to channel number. The second experiment focused on the

alignment of the nuclear image with the video image. A strong source, 1 mCi (37 Bq) of Cs-137,

was used in the ERC B058 bunker. To access this source, an experimental protocol was

developed to obtain a permit from the UOIT radiation safety officer (RSO). The purpose of this

experiment was to align the nuclear image with the center of the field of view and this required

moving the source until the center of the hotpot displayed at the center of the detector field of

view, as indicated by the red cross-hairs. To align the nuclear image, the RMD Radcam was

positioned on an angle because it was determined that the Cesium Iodide (CsI) crystal was not

parallel to coded aperture. Lastly, spatial resolution experiment was performed to determine the

limitation and appropriate applications for use. Since the spatial resolution is related to the

alignment of the nuclear and video image, same experimental protocol was followed but, another

strong Cs-137 source was also used. During experiments, it was determined that the right source

seemed always brighter than left source in nuclear image. It was either RMD RadCam was in

angle to the right, focusing right source more than left source or the photomultiplier tube was

also not parallel to the CsI crystal. There were total of six experiment that executed to find the

spatial resolution in decreasing order and found that the spatial resolution was 45.7 cm.

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1. Introduction Radiation detection has played an essential role in the study and use of nuclear materials since

radiation measurements provide a sense of safety and control to Nuclear Energy Workers

(NEWs) and the public. This represents one of the characteristics of the Radiation Measurement

Device RadCam (RMD RadCam). This gamma spectroscopic imaging system provides an

intuitive picture of the intensity, distribution, location, and energy spectrum of gamma-ray

sources (User’s Manual). This device uses a Cesium Iodide detector to generate and project a

nuclear image over a video image, obtained using a video camera, of the same field of view. The

nuclear image, obtained from the detector, is superimposed over the video image, producing a

display of any present radioactive sources in a given location within the video image (User’s

Manual). In thesis I, the pinhole collimator was used to ensure the accuracy of its functionalities,

proper calibration and alignment of the nuclear and video images. In thesis II, it outlines the

similar experiments and processes performed to achieve the calibration, alignment of the gamma

camera, as well as the results obtained from such exercises using coded aperture collimator.

Thus, the new experiment called spatial resolution will be mentioned.

2. Material and Methods

The RMD RadCam is a spectroscopic gamma ray imaging system which produces a near-real

time radiation field image, or nuclear image, superimposed over a video image of the same field

of view (User’s Manual). The system consists of many components including the RMD

RadCam detector, tungsten coded aperture collimator and pinhole collimator, video camera, data

interface box and laptop computer with the IMAGE 2000 software. The following Figure 2.1

displays the main components of the system as indicated above.

Figure 2.1: RMD RadCam components(Brochure).

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The Cesium Iodide (CsI) crystal dope with sodium, used to detect the presence of gamma

radiation, is an inorganic scintillator. When incident photons interact with the scintillator

material, the electrons of the scintillator material are raised to exited states. As these electrons

de-excite, photons in the visible light range are emitted. These photons travel to the

photomultiplier tube where they pass through a photocathode and release electrons. Dynodes

within the photomultiplier tube multiply the electrons until they reach the anode. This process

allows a respectable signal to be produced (Knoll). Since the RMD RadCam is concerned with

the origin of the incident radiation, position sensitive photomultiplier tubes are used. A CsI

crystal is used over a Sodium Iodide (NaI) crystal because it is non-hygroscopic, does not attract

or absorb moisture from the air, has a high light output and is used for applications where

mechanical stability and good energy resolution are required (Custom Scintillators & Detectors).

Depending on the application of the RMD RadCam, the position of the crystal within the

detector is adjustable. Using the adjuster knob on the back of the RMD RadCam, as noted in

Figure 2.2, the position of the crystal can be changed to a wide field of view, or narrow field of

view. The wide field of view is set when the adjuster knob is fully clockwise with the arrow

pointing towards the two dots. At this position, the crystal is at the face of the pinhole or coded

aperture collimator. The narrow field of view is set when the adjuster knob is fully counter

clockwise. At this position, the crystal is set further back from the pinhole or coded aperture

(User’s Manual). For the purpose of the experiments completed this term, the wide field of view

was primarily used.

Figure 2.12: RMD RadCam wide versus narrow view(User’s manual).

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Two types of collimators can be interchanged on the face of the RMD RadCam. These

tungsten collimators include the pinhole collimator and coded aperture collimator. The pinhole

collimator determines the location of high intensity gamma fields in a quick manner. The coded

aperture collimator is a collection many pinholes of various shapes in a specific pattern which

provide great number of events in spectrum (Brochure). In other words, coded apertures utilize

an alternate geometric method to recreate the object space. For example, when photon pass

through a pattern of open and closed apertures, this system can be thought of as an array of

pinhole imaging devices, with overlapping images (Farber).

Figure 2.3: Schematic view of RMD RadCam, using coded aperture collimator (Farber).

In addition to the coded aperture collimator, the unique holes pattern are uniquely designed

for accurate reconstruction of the nuclear and can reverse itself upon a 90° rotation (anti-mask

position) of the coded aperture. Each hole in the pattern becomes solid in the rotated anti-mask

position and each location in the 0° (mask position) that was a solid becomes a hole. Combining

the mask and anti-mask position of the coded aperture collimator enhances nuclear image quality

by reducing in the image gamma events that do not correlate with the mask/anti-mask positons of

the coded aperture (Rennie).

The video camera, mounted on the top of the RMD RadCam as seen in Figure 2.1 captures

video image of the same field view of the nuclear image generated by the detector. The images

captured by the detector and video camera are processed using the data interface box in unison

with the laptop computer. The nuclear image captured using the detector, and video image

CsI Crystal

Photomultiplier

tube

Coded aperture

Detector

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captured using the video camera are sent to the laptop where the IMAGE 2000 software

superimposes the nuclear images over a black white video image of the field of view. The

IMAGE 2000 software allows the detection period to be set using different stop conditions,

displays a color scheme for nuclear image as well as an energy spectrum of the radiation

detected. The image interval can be determined by the selection of four different stop

conditions. The conditions include max time (stops when input time is reached), max counts

(stops when input counts is reached), max time or max counts (stops when input time or counts is

reached) and max time and max counts (requires manual stop). For the experiments completed

this term, the most appropriate stop condition was determined to be max time. When a nuclear

image is generated, a color scheme is displayed to indicate the strength of the hotspot. The

intensity of the gamma radiation is presented in colour, red corresponding to higher gamma

activity. The brighter red color represents the hotspot of the gamma activity. These colours may

be adjusted based on user preference. The energy spectrum is generated based on the source(s)

being detected. The spectrum can be uncalibrated (counts as a function of channel) or calibrated

using the software (counts as a function of energy). Area of interest can be selected to show the

number counts or energy for each channel.

2.1 Calibration

To compare the previous year of calibration experiment using pinhole collimator, this

experiment was conducted using coded aperture collimator in different procedure. The energy

calibration of the spectrum generated using the RMD RadCam was completed using six point

sources: Cadmium-109 (Cd-109), Cobalt-57 (Co-57), Sodium-22 (Na-22), Cesium-137 (Cs-137),

Manganese-54 (Mn-54) and Unknown (Cs-137 & Zn-65) each with an activity of 1 µCi. In

previous year of the experiment procedure, each point sources were attached directly to the

pinhole of the camera with masking tape. For this experiment, chemistry standing was used to

hold each point sources 2.5 cm away from the coded aperture as seen in Figure 2.1.1. The

pinhole collimator area was very small that each point sources were able to attach directly to it

instead, the coded aperture collimator was too large. The calibration was obtained by running

six separate measurements of gamma emitters Cd-109, Co-57, Na-22, Cs-137, Mn-54 and

Unknown for a live time of 600 seconds, using the stop condition of max time. Upon the

completion of the outlined detection periods, the center of each peak was selected and the

channel number was recorded. Following the experiment, the spectral data was saved in tabular

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form. Using this data, the energy calibration was achieved by generating the calibration curve as

discussed in subsequent section 3.1.

Figure 2.1.1: Calibration

2.2 Alignment

To perform the alignment of the nuclear and video image using coded aperture collimator, a

strong source of 1 mCi (37 Bq) Cesium-137 (Cs-137) source was used again. For the purpose of

completing the alignment, an experimental protocol was developed to obtain a permit from the

UOIT radiation safety officer (RSO). Please refer Appendix B for more detail. This protocol was

developed by providing an overview of the need for a high activity source, outlining the method

of transporting and manipulating the source and the steps to complete the alignment during the

experiment. This exercise was conducted in the bunker, ERC B058, because of the strength

source. At the start of the experiment, an exclusion zone, as described in the protocol, was setup

using masking tape. Following the exclusion zone set-up, the RMD RadCam, data interface box,

and laptop was transported to the bunker and the video nuclear alignment was initiated using the

IMAGE 2000 software. Then, the designated nuclear energy workers (NEWs), Dr. Gloria

Orchard, used two meter tongs to maneuver the source to the first location, approximately 5

meters directly in front of the RMD RadCam. The source was moved by the NEW and various

images were taken until the nuclear image was aligned with the center of the field of view of the

detector, as indicated by the red cross-hairs. Following the nuclear alignment, the video image

was manually adjusted so the hot spot was placed directly over the location of the source. Using

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this image, the source was zoomed in on, and the alignment was “set”. This process and results

will be further discussed in section 3.2 of the report.

2.3 Spatial resolution

Since the spatial resolution is related to the alignment of the nuclear and video image, same

experimental protocol was followed. After aligning the nuclear image to center of the red cross-

hair, the designated nuclear energy workers (NEWs), Dr. Gloria Orchard, used two meter tongs

again to remove another Cesium-137 (Cs-137) source from pit #2. Using 2 m tongs, the position

of the previous Cs-137 source was adjusted on the tripod near the center of the field of view,

7.50 m away from the RMD RadCam. Then, another source was moved ~75% toward to the

right edge of the field of view of the nuclear image. The Cs-137 source that right in the center of

the field of view stayed as same instead, the Cs-137 source ~75% toward to the right edge of the

field of view of the nuclear image was moved to the left by ~25% until two sources are close

each other. This process and results will be further discussed in section 3.3 of the report.

3. Analysis

In previous year, the main purpose of thesis I was to commission RMD RadCam using

pinhole collimator by conducting two experiments: calibration and alignment. In result, there

were several problems that found during experiments: Firstly, there was problem crashing

IMAGE 2000 software during calibration experiment. Secondly, the nuclear image was unable to

be right in the center of the red cross-hair during alignment experiment. The IMAGE 2000

software crashes because of the old patched version but, as long as the software reinstall, it does

not crashes anymore. The nuclear image was unable to be right in the center of the red cross-hair

because the inside of the Cesium Iodide (CsI) crystal was not parallel to pinhole collimator.

However, as long as the RMD RamCam is in certain angle, the nuclear image was able to get

close to the center of the red cross-hair. In thesis II, the similar experiments and processes were

performed to achieve the calibration, alignment of the gamma camera using coded aperture

collimator to see if they also causes same problems. In addition to the thesis II experiment,

spatial resolution was performed to determine the limitation and appropriate applications for use.

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3.1 Calibration

The peak visible at chancel number 43 is an energy peak for the Cadmium-109 (Cd-109)

decay energies of 88 keV with 3.61 percent yield per decay. Displayed in Figure 3.1.1 is the

uncalibrated Cd-109 spectrum, counts as a function of channel, collected for a live time of 600

seconds.

Figure 3.1.1: Uncalibrated Cadmium-109 spectrum, counts as a function of channel number.

The peak visible at channel number 52 is a combined energy peak for the Cobalt-57 (Co-57)

decay energies of 122 keV and 136 keV. The energy of the peak was determined to be 124 keV

by calculating a weighted average of the two decay energies, weighting heavier towards the 122

keV energy since it decays 96.3 percent of times with this energy (Wagenaar). Displayed in

Figure 3.1.2 is the uncalibrated Co-57 spectrum, counts as a function of channel, collected for a

live time of 600 seconds.

0

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6000

8000

10000

12000

0 100 200 300 400 500 600 700

Co

un

ts

Channel Number

Cadmium-109: Counts as a Function of Channel

Number

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Figure 3.1.2: Uncalibrated Cobalt-57 spectrum, counts as a function of channel number.

Two peaks visible at chancel number 187 and 568 are energy peaks for the Sodium-22 (Na-

22) decay energies of 511 keV and 1275 keV with 180 percent yield per decay. Please note that

energy peak of 511 keV was used during calibration verification. Displayed in Figure 3.1.3 is

the uncalibrated Na-22 spectrum, counts as a function of channel, collected for a live time of 600

seconds.

Figure 3.1.3: Uncalibrated Sodium-22 spectrum, counts as a function of channel number.

The peak visible at chancel number 260 is an energy peak for the Cesium-137 (Cs-137) decay

energies of 662 keV with 85.1 percent yield per decay. Displayed in Figure 3.1.4 is the

0

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15000

20000

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30000

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Co

un

ts

Channel Number

Cobalt-57: Counts as a Function of Channel

Number

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Co

un

ts

Channel Number

Sodium-22: Counts as a Function of Channel

Number

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uncalibrated Cs-137 spectrum, counts as a function of channel, collected for a live time of 600

seconds.

Figure 3.1.4: Uncalibrated Cesium-137 spectrum, counts as a function of channel number.

The peak visible at chancel number 404 is an energy peak for the Manganese-54 (Mn-54)

decay energies of 835 keV with 100 percent yield per decay. Displayed in Figure 3.1.5 is the

uncalibrated Mn-54 spectrum, counts as a function of channel, collected for a live time of 600

seconds.

Figure 3.1.5: Uncalibrated Manganese-54 spectrum, counts as a function of channel number.

0

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4000

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7000

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Co

un

ts

Channel Number

Cesium-137: Counts as a Function of Channel

Number

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Co

un

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Channel Number

Manganese-54: Counts as a Function of

Channel Number

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Three peaks visible at chancel number 245, 383 and 494 are energy peaks for the Unknown

(Cs-137 & Zn-65) decay energies of 511 keV, 662 keV and 1115 keV with 50.6 percent yield per

decay. Please note that energy peak of 1115 keV was used during calibration verification.

Displayed in Figure 3.1.6 is the uncalibrated Unknown spectrum, counts as a function of

channel, collected for a live time of 600 seconds

Figure 3.1.6: Uncalibrated Unknown spectrum, counts as a function of channel number.

3.1.1 Calibration Verification

From the plot, it was illustrated that the relationship between channel number and energy is a

positive linear function with an equation of best fit of y = 2.1353x + 39.708, where y was the

energy and x is the channel number. The R2 value measures how closely the data conforms to

the linear relationship. This value ranges from 0 to 1, 1 representing an exact fit. The value for

the data collected, R2 = 0.9794, which confirmed that the measurements almost resemble a linear

fit. Cadmium-109 (Cd-109), Cobalt-57 (Co-57), Sodium-22 (Na-22), Cesium-137 (Cs-137),

Manganese-54 (Mn-54) and Unknown (Cs-137 & Zn-65) were used to explore their respective

calibrated energy curves. Please refer Table 3.1.1.1 to see each sources’ center channel number

of the peak. Using equation (b), the calibration line equation, the energy of each channel number

was calculated.

0

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2000

3000

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6000

0 100 200 300 400 500 600 700

Co

un

ts

Channel Number

Unknown (Cesium-137 & Zinc-65): Counts as a

Function of Channel Number

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Table 3.1.1.1: Six point sources that used for calibrated energy curve

Nuclide Center

channel

number

Energy

(keV)

FWHM Error

(FWHM/2)

Cd-109 42.84818 88 9.11289 ±4.556445

Co-57 51.75553 124 10.65918 ±5.32959

Na-22 187.47661 511 29.29028 ±14.64514

Cs-137 260.1716 662 55.18208 ±27.59104

Mn-54 404.17681 835 39.74358 ±19.87179

Unknown

(Cs-137 &

Zn-65)

503.61347

1115

49.70898 ±24.85449

y�EnergykeV� = 2.1353xchannelnumber� + 39.708

3.1.1(b)

Figure 3.1.1.1: Calibration curve, energy as a function of channel number

Using equations (c) and (d), the count rate and its associated error at each energy was

calculated.

CountRate = CountsLiveTime 3.1.1(c)

CountRateError = √CountsLiveTime 3.1.1(d)

y = 2.1353x + 39.708

R² = 0.9794

0

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600

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1200

0 100 200 300 400 500 600

En

erg

y (

Ke

V)

Channel Number

RMD Calibration Curve: Energy as a Fucntion

of Channel Number

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Completing the above, the calibrated energy spectra of Cd-109, Co-57, Na-22, Cs-137, Mn-54

and Unknown were generated as shown from Figure 3.1.1.2 to Figure 3.1.1.7 below. Refer to

Appendix A for a sample calculation of the energy, count rate, and count rate error.

Figure 3.1.1.1.2: Calibrated Cadmium-109 Count Rate as a function of energy. The

energy of each channel was calculated using equation (b). Assume no error is associated

with the energy. The count rate at each energy was calculated using equation (c). The

error associated with the count rate was calculated using equation (d). Note: the error

in the count rate is smaller than the data point.

Figure 3.1.1.3: Calibrated Cobalt-57 Count Rate as a function of energy. The energy of

each channel was calculated using equation (b). Assume no error is associated with the

energy. The count rate at each energy was calculated using equation (c). The error

associated with the count rate was calculated using equation (d). Note: the error in the

count rate is smaller than the data point.

0

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Co

un

t R

ate

(cp

s)

Energy (keV)

Cadmium-109 Count Rate as a Fucntion of

Energy

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un

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Energy (keV)

Cobalt-57 Count Rate as a Fucntion of Energy

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Figure 3.1.1.4: Calibrated Sodium-22 Count Rate as a function of energy. The energy of





Figure 3.1.1.1.5: Calibrated Cesium-137 Count Rate as a function of energy. The





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Sodium-22 Count Rate as a Fucntion of Energy

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Energy (keV)

Cesium-137 Count Rate as a Fucntion of

Energy

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Figure 3.1.1.6: Calibrated Manganese-54 Count Rate as a function of energy. The





Figure 3.1.1.1: Calibrated Unknown Count Rate as a function of energy. The energy of





The dead time of the RMD RadCam was investigated after completing the separate

measurements using Cd-109, Co-57, Na-22, Cs-137, Mn-54 and Unknown sources. The

calculated dead time were the following: Cd-109 was 3.29%, Co-57 was 1.19%, Na-22 was

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Co

un

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ate

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Manganese-54 Count Rate as a Fucntion of

Energy

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un

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Energy (keV)

Unknown (Cescium-137&Zinc-65) Count Rate as a

Fucntion of Energy

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3.94%, Cs-137 was 2.00%, Mn-54 was 2.82% and Unknown was 1.57%. Refer to Appendix A

for a sample calculation of the dead time. Assume no error exists in the time measurements.

The dead time percentage was calculated using this following equation (Orchard):

DeadTime%� = .RealTimes� − LiveTimes�RealTimes� 0 × 100% 3.1.1(e)

3.1.2 A comparison of pinhole and coded aperture collimator

For Figure 3.1.2.1 and Figure 3.1.2.2, there are two graphs of Cesium-137 (Cs-137) and

Cobalt-57 (Co-57) using pinhole and coded aperture collimator. The two graphs which shows the

major differences between pinhole and coded aperture collimator concluded that the resolution of

the peaks were much better and clear to see if coded aperture collimator was used.

Figure 3.1.2.1: Uncalibrated Cesium-137 spectrum, counts rate as a function of channel

number pinhole vs. coded aperture collimator

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Co

un

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ate

(c

ps)

Channel Number

Cs-137: Count Rate as a Function of Channel

Number

pinhole coded aperture

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Figure 3.1.2.2: Uncalibrated Cobalt-57 spectrum, counts rate as a function of channel

number pinhole vs. coded aperture collimator

3.1.3 A comparison of coded aperture collimator in narrow vs. wide view

From Figure 3.1.3.1 to Figure 3.1.3.4 there are four graphs of Cadmium-109 (Cd-109),

Cobalt-57 (Co-57), Manganese-54 (Mn-54) and Unknown (Cs-137 & Zn-65) using coded

aperture collimator in narrow and wide view. The four graphs which shows the major differences

between narrow and wide view, concluded that the resolution of the peaks are much better and

clear to see if coded aperture collimator in wide view was used.

Figure 3.1.3.1: Uncalibrated Cadmium-137 spectrum, counts rate as a function of channel

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Co

un

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ate

(c

ps)

Channel Number

Co-57: Count Rate as a Function of Channel

Number

pinhole coded aperture

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Cadmium-109: Count Rate as a Function of Channel

Number

narrow wide

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number narrow vs. wide view





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Cobalt-57: Count Rate as a Function of Channel

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narrow wide

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Manganese-54: Count Rate as a Function of Channel

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narrow wide

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3.1.4 Absolute peak efficiency and Resolution

For Figure 3.1.4.1 to Figure 3.1.4.2 there are two graphs of Absolute Peak Efficiency and

Resolution graph. Thus, both of the graphs were computed by using each peak of six point

sources: Cadmium-109 (Cd-109), Cobalt-57 (Co-57), Sodium (Na-22), Cesium-137 (Cs-137),

Manganese-54 (Mn-54) and Unknown (Cs-137 & Zn-65). In Table 3.1.4.1 below shows all the

variables that needed to calculate absolute efficiency and resolution. To find absolute efficiency,

first thing was to find the current activity of each sources. Then, it needed to find the counter

under peak. Using equation (f,g), the current activity and peak area of each source were

calculated. To see the full calculations, please refer Appendix I for more detail.

A = 3°e5λt 3.1.4(f)

Peakarea =89: − ; − 3�9< + 9=2=

:>< 3.1.4(g)

Table 3.1.4.1: Variables that used for finding absolute efficiency and resolution (Firestone)

0

1

2

3

4

5

6

7

8

9

10

-50 50 150 250 350 450 550 650

Co

un

t R

ate

(cp

s)

Channel Number

Cescium-137&Zinc-65: Count Rate as a Function

of Channel Number

narrow wide

P a g e | 24

Nuclide Counter under

peak (counts)

Activity (Bq) Branching ratio

(%)

FWHM Real time

(s)

Cd-109 12520.7 28342 3.61 9.11289 620.4

Co-57 300788.3 24198 96.3 10.65918 607.2

Na-22 26363.2 2438.3 180 29.29028 624.6

Cs-137 80852.5 29267 85.1 55.18208 612

Mn-54 64135.5 24716 100 39.74358 617.4

Unknown (Cs-

137 & Zn-65)

21614.7 22977 50.6 49.70898 609.6

Finally using equation (h,i), the current absolute efficiency and resolution of each source were

calculated. In this report, absolute peak efficiency was computed because it depends on the

detector of counting geometry and intrinsic efficiency depends on the detector material radiation

energy and physical thickness of the detector in direction of incident radiation (Gloria). In other

words, it need to factor out the solid angle while calculating intrinsic efficiency. Thus, absolute

peak efficiency and resolution were decreasing because they depends on probability of

increasing energy peak. In other words, there will be more Compton scattering as the energy

peak increases. No additional error was being created from the absolute efficiency and resolution

in this cause since they assumed to have no error associated with it. This means that the only

error present is from the measured counts error, so this error needs to be divided by either

absolute efficiency or resolution to obtain the error impacting decays per second.

Absoluteefficiency = Counterunderpeakgammaemittedbysource 3.1.4(h)

Resolution = FWHMCenterchannelnumber 3.1.4(i)

Absoluteefficencyerror = ErrorEFGAbsoluteefficency 3.1.4(j)

Resolutionefficencyerror = ErrorEFGResolution 3.1.4(k)

P a g e | 25

Table 3.1.4.2: Data for absolute efficiency and resolution

Nuclide Center

channel

number

Energy

(keV)

Absolute

Efficiency

Resolution

Cd-109 42.84818 88 0.0197 0.213

Co-57 51.75553 124 0.0213 0.206

Na-22 187.47661 511 0.00962 0.156

Cs-137 260.1716 662 0.00530 0.212

Mn-54 404.17681 835 0.00420 0.0983

Unknown

(Cs-137 &

Zn-65)

503.61347

1115

0.00305 0.0987

Figure 3.1.4.1: Absolute Peak Efficiency

-5.00E-03

0.00E+00

5.00E-03

1.00E-02

1.50E-02

2.00E-02

2.50E-02

0 200 400 600 800 1000 1200

Ab

osl

ute

Pe

ak

Eff

icie

ncy

Energy (KeV)

Aboslute Peak Efficiency Graph

P a g e | 26

Figure 3.1.4.2: Resolution

3.2 Alignment

This experiment was executed to acquire the maximum accuracy when using the RMD

RadCam. The proper alignment of the nuclear and video image provides an output with

information of the location and energy of each gamma emitter. The video camera produces a

black and white video snapshot as seen in Figure 3.2.1. The nuclear image, displayed in Figure

3.2.2, is generated from the detection of the gamma rays by a sensor head composed of, a

pinhole, a scintillator with a inorganic solid material (Cesium Iodide crystal), and a position-

sensitive photomultiplier tube. The nuclear image provides a color scale application which

reveals the intensity of radiation from each point in the camera’s field of view.

0

0.05

0.1

0.15

0.2

0.25

0 200 400 600 800 1000 1200

Re

solu

tio

n

Energy (KeV)

Resolution Graph

P a g e | 27

Figure3.2.1: Video Image (Black and White) taken in

the Bunker during alignment experiment.

Figure 3.22.2: Nuclear Image taken in the bunker

during alignment experiment. It shows hotspots

caused by the 137Cs source of 37 MBq.

The alignment is a delicate process that requires the precision of placing the source hot spot

(the nuclear image) obtained from the detector as near as possible over the center of field of

view, or the center of the red cross-hairs, of the RMD RadCam detector. Then, by manually

adjusting the video image to align the real life source location with the hot spot, alignment is

achieved.

To proceed with the alignment of the video and nuclear image there were some phases that

needed to be overcome as outlined below.

3.2.1 Phase I: Acquisition of a strong source

For the purpose of doing this experiment a strong source was required in order to locate the

source at a far distance (User’s Manual). Therefore, access to one of the strong sources located

in the pits, room B058 at UOIT was needed. Cesium-137 (Cs-137) was the chosen source due to

the fact that it was the strongest available source with an activity of 37 MBq (1 mCi). In order to

acquire a permit necessary to handle the sources, a research test plan or protocol was generated

and addressed to the UOIT Radiation Safety Officer (RSO). Refer to Appendix B for the

approved experimental protocol. A detailed description of the research test plan was outlined to

assure safety was maintained during the use of the source in ERC B058.

P a g e | 28

3.2.2 Phase II: Experiment Execution

Following the preparation of the experimental protocol, the alignment experiment in the ERC

room B058 (bunker) was executed. The purpose of this experiment was to align the nuclear

image of the source with video image of the same field of view. Before starting the experiment,

an exclusions zone was set-up, as stated in the protocol. Refer to Figure 3.2.2.1 below for an

outline of the experimental set-up in the bunker.

Figure 3.2.22.2.1: Map of room ERCB058, location of alignment experiment.

This exclusion zone was decided to ensure both NEWs and non-NEWs were not

unnecessarily exposed. Following the source manipulation steps outlined in the experimental

protocol, the source was placed in the desired location. Using the IMAGE 2000 software,

data was collected until a noticeable hotspot was generated. Using the software alignment

function, the center of field of view, determined by the red cross-hairs, was made visible over

the generated image. Several nuclear images were acquired while moving the source, in

order to determine the center of the nuclear image (User’s Manual). This required counting

with the detector for a live time of 5 minutes and collecting the data obtained from the

source. Figure 3.2.2.2 below, a sample nuclear image, is an example of the imaged

generated during the alignment.

P a g e | 29

Figure 3.2.2.2: First nuclear image obtained with

the RMD RadCam.

As shown in Figure 3.3.2.3, the source needed to be moved to the left in order to get the

center hotpot to the red cross-hairs. After several attempts to manipulate the source so the

hotspot appeared over the red cross-hairs with no success, it was determined that the CsI crystal

was not positioned perfectly parallel with the coded aperture as well. In order to achieve nuclear

alignment with the center of field of view of, the angle of the RMD RadCam was adjusted.

3.3 Spatial resolution

The main purpose of the spatial resolution is to measure of how closely lines between two

sources can be resolved in an image using RMD RadCam. In other words, it was to explore the

spatial resolution of the RMD Radcam to determine the limitation and appropriate applications

for use.

Figure 3.2.22.2.3: Second nuclear image obtained

using the RMD RadCam shows center spot farther

from the point.

P a g e | 30

To proceed with the alignment of the video and nuclear image there were some phases that

needed to be overcome as outlined below.

3.3.1 Phase I: Acquisition of strong two sources

Since the spatial resolution is related to the alignment of the nuclear and video image, same

experimental protocol was followed but, another strong Cesium-137 (Cs-137) source was also

used. Please refer section 3.2.1 for more detail.

3.3.2 Phase II: Experiment Execution

After aligning the nuclear image to center of the red cross-hair, the designated nuclear energy

workers (NEWs), Dr. Gloria Orchard, used two meter tongs again to remove another Cesium-

137 source from pit #2. Using 2 m tongs, the position of the previous Cesium (Cs-137) source

was adjusted on the tripod near the center of the field of view, 7.50 m away from the RMD

RadCam. Then, another source was moved ~75% toward to the right edge of the field of view of

the nuclear image as seen in Figure 3.3.2.1. The Cs-137 source that right in the center of the

field of view stayed as same instead, the Cs-137 source ~75% toward to the right edge of the

field of view of the nuclear image was moved to the left by ~25% until two sources are close

each other.

During experiments, right source seemed always brighter than left source in nuclear image as

seen in Figure 3.3.2.2. These problems could occurred either RMD RadCam was in angle to the

right, focusing right source more than left source or the photomultiplier tube was also not parallel

to the Cesium Iodide (CsI) crystal.

There were total of six experiment that executed to find the spatial resolution: For first four

experiment in distance of 77.5 cm, 54.6 cm. 49.5 cm and 47.0cm in decreasing order, there were

clearly two sources’ hot spots that visible in nuclear image. However, for last two experiment in

distance of 44.5 cm and 39.37 cm, only one source hot spot that visible in nuclear image. In

conclusion, the spatial resolution was 45.7 cm. Please refer Appendix C and Appendix D to see

the six figures of spatial resolution in each distances.

P a g e | 31

4. Conclusion

The RMD RadCam is a spectroscopic gamma ray imaging system which produces a near-real

time radiation field image, or nuclear image, superimposed over a video image of the same field

of view (User’s Manual). Using a Cesium Iodide crystal, tungsten coded aperture collimator or

pinhole collimator, video camera, data interface box and laptop computer with the IMAGE 2000

software, a colour coded nuclear image is superimposed over a video image, indicating the

presence and location of any radiation in the field of view of the RMD RadCam.

In thesis I RMD RadCam was commissioned using pinhole collimator. In this term, it was

commissioned using coded aperture and three major experiments including the energy

Figure 3.3.23.2.1: Experiment setup of spatial

resolution

Figure 3.3.23.2.2: Experiment 1 of spatial

resolution: 77.5 cm away from each other

P a g e | 32

calibration, nuclear and video alignment and spatial resolution were completed. The completion

of the energy calibration involved collecting six separate spectra of a 1 μCi Cadmium-109 (Cd-

109), Cobalt-57 (Co-57), Sodium-22 (Na-22), Cesium-137 (Cs-137), Manganese-54 (Mn-54)

and Unknown (Cs-137 & Zn-65) for a live time of 600 seconds. Using the channel of the peaks

and the known energy of each source, a calibration curve with the linear equation y = 2.1353x +

39.708 was obtained. Using this equation, the energy of each channel was calculated and used to

plot a calibrated spectrum of the six source measurement. The two graphs which shows the major

differences between pinhole and coded aperture collimator concluded that the resolution of the

peaks are much better and clear to see if coded aperture collimator was used.

To align the nuclear image with the video image, the use of a high activity source was

required. The source desired was the 1 mCi Cesium-137 (Cs-137) source located in the pit of the

ERC B058 bunker. In order to use the source, an experimental protocol was developed outlining

the method of source manipulation and transportation, and the steps required to complete the

alignment. This protocol was approved by the UOIT RSO granting a permit to use the high

activity source to perform the alignment. During the alignment experiment, an exclusion zone

was first established to reduce the exposure to both NEWs and non-NEWs. Then the alignment

option in IMAGE 2000 was initiated to align the nuclear image with the center of the field of

view of the detector. The Cs-137 source was placed in line with the RMD RadCam

approximately 5 meters away and an image was collected. The source was continually moved

horizontally until the source hotspot (nuclear image) was displayed at the center of the red cross-

hairs. It was determined that the crystal was not exactly parallel with the pinhole, therefore the

detector had to be angled in order to achieve perfect alignment.

After aligning the nuclear image to center of the red cross-hair, spatial resolution was

performed. Since the spatial resolution is related to the alignment of the nuclear and video image,

same experimental protocol was followed but, another strong Cesium-137 (Cs-137) source was

also used. During experiments, it was determined that right source seemed always brighter than

left source in nuclear image. It was either RMD RadCam was in angle to the right, focusing right

source more than left source or the photomultiplier tube was also not parallel to the Cesium

Iodide (CsI) crystal. There were total of six experiment that executed to find the spatial

resolution in decreasing order and found that the spatial resolution was 45.7 cm.

P a g e | 33

In conclusion, the familiarization, calibration, alignment and spatial resolution of the RMD

RadCam using coded aperture collimator presented to be successful. It is true that coded aperture

was also had same problem as pinhole but clearly, coded aperture is much more useful and

convenient tool than pinhole when it comes to collect great number of spectrum in small amount

of time.

P a g e | 34

5. Appendix A: Sample Calculation

SamplecalculationfortheenergyofthecombinedCobalt-57peak.ForCobalt-57,energies122keV86%�and136keV11%�.EnergyofcombinedpeakkeV� = 122keV × L0.860.97M + 136keV × L0.110.97M = 124keVSamplecalculationofthepeakenergycorrespondingtothechannelnumber3.1.1a�.ForCobalt-57,i.echannelnumber10.y�EnergykeV� = 2.1353xchannelnumber� + 39.708 = 2.1353 × 10 + 39.708

= 61.1keVSamplecalculationofthecountrateataspecificenergy3.1.1b�.ForCobalt-57,energy61.061keV,counts4048.394,livetime553.2seconds.CountRate = CountsLiveTime = 4048.394counts553.2s = 7.32cpsSamplecalculationoftheerrorassociatedwiththecountrate3.1.1c�.ForCobalt-57,counts4048.394,livetime553.2seconds.CountRateError = √CountsLiveTime = √4048.394counts553.2s = 0.115cpsSamplecalculationofthesystemdeadtime3.1.1d�.ForCobalt-57,livetime600seconds,realtime611seconds.DeadTime%� = .RealTimes� − LiveTimes�RealTimes� 0 × 100% = L607.2s − 553.2s607.2s M × 100%

= 8.89%Samplecalculationoftheerrorassociatedwiththecalibrationcurve3.1.1e�.ForCobalt-57.CalibrationError = FWHM2 = 10.659182 = ±5.33Samplecalculationofactivityandpeakareaneededtocalculateabsoluteefficiency3.1.4f,g�.i� ActivityforCobalt-57.GivensCurrentActivityJan162015�ManufactureddateAug012014�t = Jan162015 − Aug012014 = 0.46yearsAo=1µciTT UV = 0.75years

P a g e | 35

SolutionsA = AWe5XYA = 1μci�e5L [\U�].^_`abcdM].ef`abcd� = 0.654μciii� PeakareaforCobalt-57.GivensCi=336136.3878countsA=Channelnumber25B=Channelnumber66CA=1180.83countsCB=543.4696countsSolutionsPeakarea = 8Ch − B − A� Ci + Cj2

j

h>i

Peakarea = 8336136.3878counts − 66 − 25� 1180.83counts + 543.4696counts2j

h>i= 300788countsSamplecalculationoftheabsoluteefficiencyandresolution3.1.4h,i�.i� AbsoluteefficiencyforCobalt-57.GivensCounterunderpeak=300788.3countsActivityforCobalt-57=0.654µciReal-time=607.2secondsBranchingratio=96.3%SolutionsAbsoluteefficiency = Counterunderpeakgammaemiitedbysource

= 300788counts0.654μci × 3.7 × 10T]BqCi × Ci10f × 607.2seconds × 0.0963 = 0.0213

ii� ResolutionforCobalt-57.

P a g e | 36

Resolution = FWHMCenterchannelnumber = 10.6591851.75553 = 0.206Samplecalculationoftheerrorabsoluteefficiencyandresolution3.1.4j,k�i� AbsoluteefficiencyerrorforCobalt-57.AbsoluteEfficiencyError = ErrormndAbsoluteEfficiency = 0.115cps0.0213 = ±5.40ii) Resolution error for Cobalt-57

ResolutionError = ErrormndResolution = 0.115cps0.206 = ±0.558

P a g e | 37

6. Appendix B: Experimental Protocol

RMD RadCam

Research Test Plan

Revision 1

Proposed Dates of Experiment:

Friday March 06, 2015

Location:

ERC B056 and B058, UOIT, Oshawa, ON

Sources: 2 x 37 MBq 137Cs

Personnel Involved:

Dr. Anthony Waker

Dr. Gloria Orchard

DuHwan Kim

Work Plan Authorization:

Name Title Signature Date

Tanya Neretljak UOIT RSO

Anthony Waker Supervisor

Gloria Orchard Co-Supervisor

Overview:

The RMD RadCam is a spectroscopic gamma-ray imaging system designed for superimposing a

nuclear image of gamma radiation over a black and white video image for the same field of view.

In thesis I, preliminary tests were performed in September of 2014 using a small button source (1

µCi 137Cs). The source strength was determined to be too low for detection at moderate

distances and alignment of the nuclear and video images. Therefore, one larger sources of

cesium-137 (37 MBq) is required. In thesis II, there are two parts of the experiments that will be

performed using the RMD RadCam to align the nuclear image with the video image and spatial

resolution with using coded aperture.

Anticipated Doses:

The calculations of the expected dose are included in Appendix A.

General Comments:

P a g e | 38

1. The source will be handled at all times in accordance with the as low as reasonably

achievable (ALARA) principle.

2. The source will only be handled by designated Nuclear Energy Workers (NEW) at UOIT.

3. Any NEWs handling the sources will be equipped with an electronic personal dosimeter

(EPD) during unpacking, transport, use and packing. The EPD will be set to alarm at a

level of 0.2 mSv.

4. A calibrated radiation survey meter will be used to monitor radiation fields during

unpacking, transport, use and packing.

5. Minimum safe distance will be maintained between any persons and the source at all

times as outlined in Figure 1 by the indicated exclusion zone.

6. The source will only be handled using 2 m tongs.

7. The source will never be left unattended.

8. The source will be returned to pit #1 in ERC B058 at the end of experiment period.

Transportation of Sources from/to Storage:

1. The source will be moved from the pit in ERC B058 and placed onto the tripod using 2 m

tongs by Anthony Waker and/or Gloria Orchard. It will be monitored by a calibrated

radiation survey meter.

2. Experiments will be conducted as per the tests outlined below.

3. At the end of the experiments for each day, the source will be returned to the pit in ERC

B058 reversing the steps above.

Manipulating Sources in Room:

1. The source will remain in the pit until all other experimental material and hardware are

setup.

2. A platform to hold the source will be placed in the room at required location(s). Refer to

Figure 1 for the map of the experimental setup.

3. When the experiment is ready to begin, the source will be removed from the pit, using the

2 m tongs, and placed on the platform. This procedure will take no more than 30

seconds.

4. The radiation fields at points of entry to the room will be monitored and recorded.

5. Non-NEWs will remain outside of the exclusion zone at all times. Once the source is in

place, those manipulating the source will retreat to outside the exclusion zone and the

dose rate will be monitored.

6. When the source requires repositioning in the room, 2 m tongs will be used to move the

source.

7. At the end of the experiment, the source will be returned to the pit in ERC B058.

P a g e | 39

Figure 1: Map of experimental setup in ERC room B058. Note that non-NEWs will remain

outside of the exclusion zone at all times.

Experiment #1: Image Alignment using one Cesium-137

Objective:

To align the nuclear image of the RMD RadCam with the video image.

Procedure:

1. Setup RMD RadCam and software at the east side of ERC B058. This will be the

location of all personnel, the RMD RadCam and the computer when not in operation

mode.

2. Initiate the “Video Nuclear Alignment” of the RMD RadCam using software. Remove

the Cesium-137 source from pit #2 (see Figure 1) using 2 m tongs and place it on the

tripod near the center of the field of view, 7.50 m away from the RMD RadCam and take

an image of the source.

3. Using 2 m tongs, adjust the position of the source on the platform and take an additional

image of the source. Repeat this step until the nuclear image is superimposed on the

center of the red cross-hair displayed on the software of the computer screen.

4. Manually adjust the video camera while images are being taken until the video image of

the source is superimposed on the nuclear image of the source.

5. Using the 2 m tongs, move the previous source ~75% toward the edge of the field of view

of the nuclear image. Acquire the nuclear image and magnify the video image using the

computer software to achieve the alignment of nuclear and video image.

P a g e | 40

Experiment #2: Spatial resolution using two Cesium-137

Objective:

To explore the spatial resolution of the RMD RadCam to determine the limitation and

appropriate applications with using coded aperture.

Procedure:

1. Remove another Cesium-137 source from pit #2 (see Figure 1) using 2 m tongs.

2. Using 2 m tongs, again adjust the position of the previous Cesciusm-137 on the tripod

near the center of the field of view, 7.50 m away from the RMD RadCam and take an image of

the source.

3. Using the 2 m tongs, move another Cesium-137 the source ~75% toward the edge of the

field of view of the nuclear image.

4. The Cesium-137 source that right in the center of the field of view will not be moved but,

only the Cesium-137 source ~75% toward the edge of the field of view of the nuclear image will

be moved to the left by ~25% until two sources are close each other.

5. Return the two sources to the bunker using the 2 m tongs after finishing all the

experiments.

Appendix A – Dose Calculations

Cs-137 gamma constant = 1.02 × 105e opq×orsc×tju

Cs-137 contact dose rate = 12.5 opqsc×tjufor encapsulated sources

UOIT Action level = 0.3 mSv (1/3 CNSC public whole body dose limit)

Benchmark: 1 meter dose (two sources):

At 1 meter, the dose rate is 7.55 µSv/hr

The time to get to action level at 1 meter is 39.8 hours

Removal of source from pig using tongs: 2 m dose (two sources):

This conservatively assumes that the dose at 2 m (tong length) is the same as the whole body dose.

At 2 meter, the dose rate is 1.887 µSv/hr

The time to get to action level at 2 meter is 159 hours

Average distance of personnel from sources during experiment: 5.15 meter (two sources):

At 5.15 meter, the dose rate is 0.292 µSv/hr

The time to get to action level at 5.15 m is 1054 hours

P a g e | 41

7. Appendix C: Table of Spatial resolution ULT: 100% & LLT:

60%

P a g e | 42

8. Appendix D: Table of Spatial resolution ULT: 80% & LLT: 60%

P a g e | 43

9. References

i) Farber, M. A. (2013). Coded-Aperture Compton Camera for Gamma-Ray Imaging. The

University of Arizona Retrieved from:

http://arizona.openrepository.com/arizona/bitstream/10150/311555/1/azu_etd_13097_sip

1_m.pdf

ii) Firestone, R. B. (2000). Exploring the Table of Isotopes. Ernest O. Lawrence Berkeley

National Laboratory Retrieved from: http://ie.lbl.gov/education/isotopes.htm

iii) Knoll, G. F. (2010). Radiation Detection and Measurement. Danvers, MA: John Wiley &

Sons, Inc.

iv) Orchard, G. (2012). Lecture 2B, 3A - General Properties of Radiation Detectors

Continued. RADI 4550 Lecture Notes. University of Ontario Institute of Technology.

v) Rennie, G (2006). Imagers Provide Eyes to See Gamma Rays. Lawrence Livermore

national laboratory Retrieved from: https://str.llnl.gov/str/May06/Fabris.html

vi) Unknown. Custom Scintillators & Detectors. CA: San Rafael: Berkley Nucleonics

Corporation. Retrieved from:

http://www.berkeleynucleonics.com/products/Custom_Scintillators_Probes.html

vii) Unknown. RMD RadCamTM Spectroscopic Gamma-Ray Imaging System Brochure.

Watertown, MA: RMD Inc.

viii) Unknown. RadCamTM User’s Manual. Watertown, MA: RMD Inc.

ix) Wagenaar, D. J. Cobalt-57 Decay. JPNM Physics Isotopes. Retrieved from:

http://www.med.harvard.edu/jpnm/physics/isotopes/Co/Co57/dec.html

RMD RadCam Thesis II report - du.kim

Documents

spatial resolution

anthony waker

gloria orchard

acquisition of strong

experiment execution

calibration verification

thesis advisors

radiation science