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12th Int. Beam Instrum. Conf.
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QUALITY ASSURANCE OF PROTON BEAM PROFILE USING PHOSPHORSCREEN AND TE-COOLED CMOS CAMERA*
Gwangil Jung†, Young-Seok Hwang, Young Jun Yoon
Korea Atomic Energy Research Institute, Gyeongju-si, Republic of Korea
Abstract
The Korea Multi-Purpose Accelerator Complex (KOMAC) operates a 100 MeV proton linear accelerator,
providing a high flux proton beam at the TR103, a generalpurpose irradiation facility. Ensuring uniform irradiation ofsample with protons is critical, necessitating confirmationof beam profile uniformity through the quality assurance(QA) process. To address this, a real-time and in-situ proton beam profile monitoring system was recently introduced and tested at the TR103. This system includes a P43
phosphor screen and TE-cooled CMOS camera, which captures images of the emitted light from protons with energies of 20, 50, and 100 MeV incident on the screen. Subsequent post-processing, such as background subtraction, image smoothing, geometrical correction, was performed on
the image data. The measured beam profiles using thephosphor screen and cooled camera were then compared tothose obtained using Gafchromic filmTM, a widely used dosimeter in radiation measurements. Additionally, the linearity between light output and beam flux was measured toestablish a quantitative relationship. This study presents
the test results of the proton beam profile measurement using the phosphor screen and TE-cooled CMOS camera,
demonstrating its potential as an effective tool for quality
assurance in proton beam irradiation experiments at theTR103 facility.

INTRODUCTION
Since 2013, KOMAC has operated a 100 MeV proton
linear accelerator, facilitating various proton beam irradiation experiments. To ensure optimal experimental conditions and minimize irradiation errors, a rigorous quality assurance (QA) process for proton beam profiling is essential
to achieve uniform proton irradiation within the sample.
The uniformity criteria, defined as the difference between
the maximum and minimum intensity divided by the mean
intensity, must meet a threshold of 10% within the target
diameter.
The TR103, a general-purpose irradiation facility at KOMAC, has used film dosimetry for beam profile QA. However, film dosimetry lacks real-time and in-situ monitoring
capabilities due to the need for scanning to acquire beamprofile data and its susceptibility to saturation under continuous irradiation of high-flux proton. To address theselimitations, a recent advancement introduced the use of aP43 phosphor screen and TE-cooled CMOS camera forreal-time and in-situ proton beam profile monitoring.
This study aimed to verify the accuracy of the P43 phosphor screen and CMOS camera system and integrated it
into the quality assurance process. An experiment was conducted to capture the light response of the phosphor screen.

EXPERIMENTS AND DISCUSSTION
Phosphor Screen and Cooled Camera
Proton irradiation tests were performed at TR103 with aflux of approximately 1010 to 1011 particle/(cm2∙pulse). The
pulsed proton beam was accelerated to energies of 20, 45,and 102 MeV, and its energy was attenuated by 15, 42, and100 MeV, respectively, as it passed through the beam window and air before reaching the target point. The beam profile monitoring system primarily consisted of a phosphor
screen, where light is emitted as protons deposit energy,
and a real-time capturing camera. The phosphor screen waspositioned 1.5 m away from the beam window, tilted at a45-degree angle relative to the beam path, while the camera
was placed 1 m perpendicular to the screen for real-time
imaging of the emitted light (Fig. 1).
The phosphor screen used in this study consisted of aP43 (Gd2o2S :Tb) layer on an Al substrated, providing adetection area of 310 mm × 310 mm and a peak wavelength of 545 nm [1]. With a decay time of 1 ms to 10%
and high light efficiency, the phosphor screen proved suitable for real-time light emission detection. The TE-cooled
CMOS camera (ASI183MC Pro, ZWO) utilized in the setup had a sensor size of 13.2 mm × 8.8 mm and a thermoelectric cooler capable of cooling sensors down to-10℃ [2]. Figure 2 illustrates the arrangement of the P43
phosphor screen and the camera. To minimize image noise
and avoid saturation at high light outputs, the camera

Figure 1: View of general-purpose irradiation facility,
TR103 (top) and configuration of device layout (bottom).

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settings were optioptimzed, utilizing the lowest ISO andappropriate exposure time.
Figure 2: Setup of the P43 phosphor screen.

In general, the presence of hotspots in an image is directly
related to the amount of radiation accumulated in the sensor.
Cooled cameras demonstrated improved radiation resistance due to the reduction of leakage current in defectivesensors with decreasing temperature [3]. To validate thenoise reduction effect in the high-radiation setting, an experiment was conducted to measure the number of hot pixels while cooling the pixels decreased accordingly andeventually stabilized at -10 ℃, as depicted in Fig. 3.

Image Post-Processing

Figure 2: Setup of the P43 phosphor screen.

Figure 3: The number of hot pixels as a function of camera
temperature.

To enhance the accuracy of beam profile measurements,
a series of post-processing steps were employed to approximate the actual beam shape from the raw image data, asillustrated in Fig. 4. Initially, the raw image contained thewhite screen background and the grid, which are eliminated by subtracting pre-captured background images. Additionally, a Gaussian filter was applied to smooth the image. Considering the 45-degree tilt of the phosphor screen
from the beam path, the length ratio of the horizontal axis
was adjusted to reconstruct the actual beam shape. To establish X-Y coordination by converting pixels to millimetres, a Region of Interest (ROI) was selected, and the actual
length of the ROI was divided by the number of pixels corresponding to that length.
An algorithm was developed to calculate the intensity
uniformity within the diameter and identify the position atwhich the uniformity of a given diameter is minimized. A
dedicated software tool was designed to facilitate the selection of beam profile image and streamline the post-processing of image data, as depicted in Fig. 5. These
measures collectively contributed to increasing the accuracy and reliability of the beam profile measurements.

Figure 4: Post-processing of image data using Python.
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12th Int. Beam Instrum. Conf.
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Content from this work may be used under the terms of the CC-BY-4.0 licence (© 2023). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI

12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3

IBIC2023, Saskatoon, CanadaJACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - W E P 0 1 3Table 1: Minimum Uniformity, FWHM and Sigma of theBeam Profile Measured by Phosphor Screen and Film for
Each Incident Proton Energy
15 MeV
42 MeV
100 MeV
HD-V2

ScreenHD-V2ScreenHD-V2Screen

11.9

9.8

7.5

7.3

6.2

6.5

31.1

25.6

20.2

19.8

16.1

17.1

25.3

28.4

34.5

34.8

36.1

37.1

FWHM-ver(mm)

33.7

34.5

33.6

34.5

38.737.1

𝜎-hor(mm)

21.5

24.2

29.3

29.5

30.4

31.9

𝜎-ver(mm)33.7

Uniformity
in 30mm-∅(%)
Uniformity
in 50mm-∅(%)
FWHM-her(mm)

34.5

34.5

34.5

38.7

37.1

Figure 5: Uniformity calculation result window of beamprofile analysis software. Software calculates the uniformity of intensity and find the position at which the uniformity of a given diameter is minimized.

Proton Beam Profile Measurement
To compare the beam profiles obtained from the phosphor screen and film, both were subjected to 5 pulses ofproton beam and subsequently normalized based on themaximum intensity value. Figure 6 presents the horizontal
and vertical beam profile plots as measured by the phosphor screen. Gaussian function fitting was employed toevaluate the value of sigma and full width at half-maximum (FWHM) for the beam profile data. The minimum

Figure 6: The horizontal and vertical beam profile plotsmeasured by phosphor screen.
uniformity values within the Region of Interest (ROI) for
diameters of 30 mm and 50 mm were calculated. Table 1
displays the minimum uniformity, FWHM, and sigma values of the beam profiles measured by the phosphor screen
and film for each incident proton energy.
At incident energies of 42 MeV and 100 MeV, both the1D profiles obtained from the phosphor screen and film
display differences of less than 2 mm in both directions,while the uniformity of the 2D profile show differences
within 10% for both diameters. In the case of the incident
energy of 15 MeV, the 1D profile demonstrates differencesof less than 3mm in both directions, and the 2D profiles
exhibits differences within 20% for both diameters. These
results indicate a good level of agreement and consistency
between the beam profile measured using the phosphor
screen and film method across various incident proton energies.
A test was conducted to verify the linearity between light
output and beam flux. The faraday cup and phosphor
screen were utilized simultaneously to measure beam flux
and light output as the beam pulse width was increased.
The beam fluxes were obtained as a function of light output
for each proton energy and then normalized by the maximum value. Figure 7 illustrates the linearity between beam
flux and light output for each proton energy. The corresponding R-square values for 100 MeV, 42 MeV, and
15 MeV were found to be 0.995, 0.991 and 0.961, respectively. The results demonstrated a satisfactory linearity between beam flux and light output across the entire range
without any signs of saturation. However, it was observedthat as the proton energy decreases, the linearity of beam
flux and light output diminishes due to the influence ofWEP013
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JACoW Publishing
ISSN: 2 6 7 3 - 5 3 5 0
d o i : 1 0 . 1 8 4 2 9 / J A C o W - I B I C 2 0 2 3 - W E P 0 1 3high linear energy transfer (LET), resulting from the low
proton energy, which causes a quenching effect on light intensity [4].

CONCLUSION
For real-time and in-situ proton beam profile monitoring,the integration of a P43 phosphor screen and a TE-cooled
CMOS camera was implemented. To validate the accuracyof this monitoring system and incorporate it into the quality
assurance process, an experiment was conducted to capturethe light response of the phosphor screen using the CMOScamera. The acquired beam profile data from the phosphor
screen were compared with those obtained using
gafchromic film. Post-processing of the image data
involved background subtraction, image smoothing,geometrical correction, and the selection of Region ofInterest (ROI) and X-Y coordination.
Comparison of beam uniformity measured using thephosphor screen and film revealed that incidents with energies of 42 MeV and 100 MeV displayed differences
within 10% in both diameters, while the incident energy of15 MeV exhibited a difference of approximately 20% in
both diameters. The linearity between light output andbeam flux was found to be excellent, demonstrating a consistent relationship throughout the entire range without any
indication of saturation.
Overall, the introduction of this novel beam profile monitoring system is expected to facilitate in-situ quality assurance processes, providing real-time monitoring capabilities
and improving the accuracy and reliability of proton beamprofiling at the facility.

REFERENCES[1] http://proxivision.de/product/scintillatingscreen/[2] http://astronomy-imaging-camera.com/product/asi183mc-pro-color/[3] A. Huber et al., “Response of the imaging camera to hard radiation during JET operation”, Fusion Engineering and Design, vol. 123, pp. 669-673, 2017.
[4] J. B. Birks, The Theory and Practice of Scintillation
Counting, Oxford: Pergamon, 1964.

Figure 7: Beam flux as a function of light output for protonenergy of 100, 42, 15 MeV.

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12th Int. Beam Instrum. Conf.
ISBN: 9 7 8 - 3 - 9 5 4 5 0 - 2 3 6 - 3