The document describes designing and testing a low-cost gamma radiation detector using a smartphone camera. The author tests various parameters of the smartphone detector such as calibration with radiation sources, thermal noise, distance effects, shielding effects, timing resolution, and efficiency compared to semiconductor detectors. Although not as efficient as professional detectors, the smartphone detector provides a low-cost option for estimating radiation dose that is more accessible than specialized equipment.

1. Designing and Testing a Low Cost
Gamma Detector
A project submitted to the National University of Ireland, Galway in partial
fulfillment for the degree of BSc (Hons) in Physics with Medical Physics.
By Christopher Mitchell
Department of Physics,
National University of Ireland, Galway
Project Supervisor: Dr. Mark Foley
April 2015

2. i
Signed Copy of Plagiarism Statement
National University of Ireland, Galway
School of Physics
Fourth Year Laboratory Programme
Plagiarism Statement
I have received copies of (1) the plagiarism guidelines for the Fourth Year
Physics programme and (2) the University Code of Practice for Dealing with
Plagiarism. I have read and understood these documents.
All work that I shall submit for assessment purposes shall be my own, and
written in my own words, except where explicitly referenced using the
appropriate norms and formats.
Name (Block Capitals Please): _____________________________________________
Signature: _____________________________________________
Date: _____________________________________________

3. ii
Abstract.
Smartphone cameras have the ability to be converted into ionising radiation
detectors by covering the lens. The lens detects high-energy photons emitted by
a variety of gamma radiation sources. The gamma detector is limited by its
inability to differentiate between the energies of the radiation fields it is
detecting, however the detector can be calibrated to give the estimated dose
(μSv/hr). It has the ability to be used as a personal dosimeter. The detector is not
very sensitive and is subject to thermal noise. The radiation intensity detected
varies from phone to phone. However linearity plots of counts versus dose rate
can be obtained regardless of noise or sensitivity values. The measurements of
the detector are sensitive to the position and angle of the source. The following
parameters were tested as part of this investigation: Calibration of device with
sources, thermal noise, distance of source, shielding effects, resolving time of
detector, variance of count rate with angle and absolute efficiency comparison to
semiconductor detectors. The detector follows the radiation theory tested such
as the inverse square law and the law of absorption. The Smartphone detector is
a low cost dose meter that can provide estimated dose readings of radiation
sources, although it is not as efficient as other semiconductor detectors, this low
cost detector is much cheaper than its professional detector counterparts and
there are more smartphones available than detectors. So the smartphone at
times may be the best gamma detector available.

4. iii
Acknowledgments.
I would like to thank Dr. Mark Foley for his consummate guidance, knowledge
and patience during this project.
I would also like to thank all the academic and technical staff of the Physics
department including James Nallen for his support during this undertaking.
Finally I would like to thank Robert Johnson for his help with understanding the
concepts behind, and providing the data for the Cadmium Telluride (CdTe) x-ray
and gamma ray detector.

5. iv
Table of Contents
Signed Copy of Plagiarism Statement...........................................................................i
Abstract..................................................................................................................................ii
Acknowledgments............................................................................................................ iii
Introduction .........................................................................................................................1
Radioactivity .................................................................................................................................1
Decay of the Nucleus.............................................................................................................................2
Background Radiation.......................................................................................................................................2
Gamma Radiation........................................................................................................................................3
The inverse Square Law ....................................................................................................................4
Detectors ..............................................................................................................................................5
How a CMOS Sensor Detects Radiation.........................................................................6
Summary...................................................................................................................................7
Aims.........................................................................................................................................7
Materials................................................................................................................................7
Method....................................................................................................................................8
Results .................................................................................................................................18
Discussion .......................................................................................................................... 27
Conclusion.......................................................................................................................... 29
Limitations......................................................................................................................... 30
Recommendations...........................................................................................................30
References.......................................................................................................................... 31

6. 1
Introduction
Radioactivity
Alpha, Beta and Gamma emission occur as a result of the decay of unstable nuclei
into less energetic nuclei. Respectively, these forms of emission consist of He4
nuclei, positron or electron, and high-energy photons. The types of decays that
occur depend on the instability of the nuclei. Some radioactive materials emit
more than one type of radiation. This is the case if the original radioactive parent
nuclei produce in decay chain radioactive daughter nuclei. The three forms of
radiation can de deflected and separated by a magnetic field.
Alpha decay occurs with the emission of a helium nucleus with two neutrons and
two protons, which results in the original nuclei being reduced by an atomic
number and mass of two and four respectively.
If a nuclei that has too many or too few neutrons with respect to the number of
protons can cause the nuclei to become unstable. If the nuclei are flooded with
neutrons, there is a probability that one will undergo a change into a proton with
the emission of an electron and an antineutrino. This electron has a high rate of
energy and is referred to as a beta particle. This process is called β- decay.
Likewise if there are too few protons present then there is a probability that one
will change into a neutron with the emission of a positron (which is a negative
electron) and a neutrino. This process is called β+ decay, however the positron is
very difficult to detect as it usually reacts with an electron and annihilates
producing gamma rays in the form of high-energy photons.
Gamma radiation occurs as a result of alpha and beta decay causing the nucleus
to be left in a high-energy state. The nucleus can emit photons to go from a
higher energy level to one of a lower energy level. These photons have very high
energies and are called gamma rays. (Siegbahn, 2012)
Figure 1. Radioactivity (Alpha, Beta and Gamma emission) [7]

7. 2
Decay of the Nucleus
The decay of a nucleus occurs randomly. In each infinitesimally event of time,
there is a probability of the unstable nuclei in the radioactive sample to decay.
Poisson statistics can be used to describe the number decays that occur in a
certain finite period of time.
𝑃𝑟𝑜𝑏𝑎𝑏𝑖𝑙𝑡𝑦 𝑜𝑓 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑒𝑐𝑎𝑦𝑠 =
(𝜆𝑡) 𝑛
𝑒−𝜆𝑡
𝑛!
λ is the mean number of decays in a second; n is the probability of the number of
decays that occur in a time interval of t, n is a factorial.
The square root of the number of decays that occur is equal to the standard
deviation of the number of decays that occur throughout a certain time interval t.
The standard deviation is used to see if a measured set of counts deviates from
the overall mean of the results. This relationship between the mean and the
standard deviation can be used to gauge the number of counts that are needed to
achieve a certain level of accuracy. √𝜆 Represents the average number that
deviates from the mean λ, therefore the
√𝜆
𝜆
=
1
√𝜆
so the accuracy is increased as
the square root of the number of counts. (Wahlström, 1995)
Background Radiation
External sources have an impact on any recorded counts of a detector. It
represents a percentage of all recorded count events. These external background
counts can be as a result of sources including cosmic rays, or radioactive
elements that are airborne or found in close by building materials or even other
radioactive sources which are present close enough to be detected as they are
not correctly shielded with e.g. lead. Before any radiation counting experiment is
attempted, the background radiation of the surrounding area must first always
be recorded. The data measured can then be more accurately determined for
any source by subtracting the recorded value for the background radiation. The
recorded radiation values can never be fully accurately determined, as the count
events of radiation emitted by both radioactive sources and naturally occurring
background radiation are completely random events. This introduces a certain
level of uncertainty and noise into any data measurements. As Poisson statistics
can be used to determine the background radiation, it follows that the
uncertainty will be the square root of the mean number of background counts.
The total uncertainty of different sources is calculated by using the following
equation. 𝜎𝑡𝑜𝑡𝑎𝑙
2
= 𝜎𝑠𝑜𝑢𝑟𝑐𝑒 1
2
+𝜎𝑠𝑜𝑢𝑟𝑐𝑒 2
2
….
The effects of the uncertainty of noise caused by the background radiation
counts on the accuracy of recorded counts can be decreased by increasing the
count rate of the radioactive source in comparison to the count rate of the
background radiation. Other methods of decreasing the effects of added
background radiation include moving the source closer to the detector or
increasing the amount of radioactive source used to increase the count rate ratio
to background counts. Also the effects can be negated by using shielding such as
lead, around the source being measured to block out the effects of the
background counts. (Knoll, 2010) [5]

8. 3
Gamma Radiation
Gamma radiation is comprised of photons with very high energies. These
photons have wavelengths equivalent to less than 10-10 meters. Visible light has a
wavelength of approx. 10-6m. The emission of gamma particles comes before
alpha or beta emission, which leaves the nucleus in an excited state. A nucleus in
an excited state can go to a lower state by emitting a photon such as a gamma
ray. This is comparable to an emission of a photon and an electron changes from
a higher to a lower orbital. The nuclear energy state spacing occurs with energy
in the order of Millions of electron Volts (MeV). Electron orbital energies only
occur in the order of electron Volts (eV). The energy of a photon E = hf can be
substituted into the equation describing wavelength and frequency, c = fλ
λ =
c
f
=
hc
E
=
1240 MeV ∗ femtometers
1 MeV
= 1240 fm
In the visible light, a material absorbs gamma rays at a linear rate. An equal
fraction of the remaining light is absorbs for every unit of distance that the
radiation travels through the material. Such as if radiation is passed through
absorption plates made up of the same materials of equal thickness.
The half thickness of the material is the thickness at which it absorbs half the
gamma rays that pass through it. After the gamma rays pass through the first
absorbing plate, the intensity of the rays is halved. After it passes through a
second plate, then the rays half again leaving one quarter of the original
intensity. After it passes through a third plate, then the intensity is one eight.
This is an exponential decrease, which is described by the Lambert’s law.
I(X) = I0 e−μX
ln (
I
I0
) = −μX
μ is the coefficient of linear absorption.
The half thickness of a material is given by the following equation.
I (𝑋1
2
) = 0.5 I0 = I0e
−μ𝑋1
2
𝑋1
2
=
−ln(1 2)⁄
μ
=
0.693
μ
Gamma rays can be absorbed by a number of ways including pair production at
high energies, Compton effect at medium energies and the photoelectric effect at
very low energies. The μ (the coefficient of linear absorption) is calculated by a
combination sum of all three processes. (Lilley, 2013) [5]
Figure2. Compton Scattering, Pair Production, Photoelectric effect
[8],[9],[10]

9. 4
μ = τ(Photoelectric) + 𝜎(𝐶𝑜𝑚𝑝𝑡𝑜𝑛) + 𝐾(𝑃𝑎𝑖𝑟 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛)
A number of different factors also decrease the beam energy such as Bragg
scattering, Rayleigh scattering, Photodisintegration and nuclear resonance
scattering.
The absorption of Gamma by the photoelectric effect occurs as a result of gamma
rays ionising an atom. The density of the interacted material is proportional to τ
the rate of absorption by photoelectric effect. This increases with atomic
number,
𝜏 = 0.0089𝜌
𝑧4.1
𝐴
𝜆 𝑛
ρ is the materials density, the atomic number and mass are Z and A respectively,
λ is the wavelength and n is 3 for Carbon, Nitrogen and Oxygen and 2.85 for the
rest of the elements that have an atomic no less than Fe (Iron). The greater the
wavelength, the stronger the photoelectric effect due to lesser energetic gamma
rays. The photoelectric effect greatly increases with atomic number. (Gilmore,
2011) [5]
The inverse Square Law
The direction is random of particles that are emitted during nuclei decay. So the
emission of the particles is evenly distributed in every direction if the absorption
is neglected in a radioactive source. If they are centered on the source, a set of
concentric spherical surfaces surrounding it and none of the particles are
absorbed, then each of the spheres has more of a surface area then the inner
sphere. As a result there is a higher density of radiation nearer the source. The
surface area of a sphere is
𝑠 = 4𝜋𝑑2
Even if absorption radiation is not present, the radiation intensity levels
decrease as a reciprocal of distance from the source squared. This is the inverse
square law. (Bloor, 2013)
The fraction of radiation totally emitted from a source that is placed near the
detector window of a Geiger molar counter and detected in the direction of the
window, is given by the geometry G factor.
𝐺 =
𝑆′
4𝜋𝑑2
A Geiger molar counter has a round window with a radius r, and an area of πr2,
as long as the source is not placed directly at the detector window. (Spiers, 1941)
𝐺 =
𝜋𝑟2
4𝜋𝑑2
=
𝑟2
4𝑑2
When the detector is moved away from the radiation source, there is an increase
in the total spherical surface area of the window by a distance squared. However
the enclosed area of S’ stays the same throughout. The inverse square law results
in a drop off in intensity of radiation levels as the particles spread away from the
source. If the sources are moved away from the detector at different distances, or
likewise the geometry size of the detector window is changed, then the G factor
must be used to compare any results. The benefits of the inverse square law are
that it can be implemented to change the count rate if it is too low by simple
moving the source closer to the detector window, or vice versa if it is too high.

10. 5
Figure 3. The Inverse Square Law [11]
Detectors
There are a wide variety of Semiconductor detectors available fro the detection
of ionising radiation. They usually implement a semiconductor such as
germanium or even silicon to detect the absorption of photons.
Photons are not directly in the form of ionising radiation particles e.g. gamma
particles. However the energy of the photons can be converted into particles
charged with kinetic energy. The energy of these charged particles are then
measured to obtain the energy of the gamma particles.(Bushberg and Boone,
2011)
Scintillation detectors : A gamma ray interacts with the scintillator e.g. Thallium-
activated sodium iodide (NaI(TI)). This produces a pulse of light that is
converted into an electrical pulse by a Photo Multiplier Tube (PMT). The PMT
consists of a photocathode, a focusing electrode and dynodes that multiply the
number of electrons, which strike it.
There are two types of scintillation detectors that will be used. A well detector
has a large 3”x 3” detector window. Shielding which allows it to obtain more
accurate results surrounds the detector. The second type is just a stand alone
(NaI(TI)) detector which has the PMT built into its body. The well scintillation
detectors have a higher efficiency at recording the decays of a radioactive source
due to the shielding. [1]
Another type of detector is a Cadmium Telluride (CdTe) detector. This is a
thermoelectrically cooled X-ray detector, which used CdTe diodes in a
preamplifier. The Gamma rays interact with the CdTe atoms in the preamplifier
to create on average one electron hole pair for every 4.43KeV it detects as being
lost in the CdTe. The efficiency of the detector to stop incoming radiation
increases by increasing the thickness of the CdTe. [4]
Figure 4. (NaI(TI)) Figure 5. (NaI(TI)) Well Figure 6. CdTe

11. 6
How a CMOS Sensor Detects Radiation
A CMOS sensor creates an image using pixels, which are usually comprised of
several million-sensor cells. In the typical use of the camera, it creates an image
by implementing the photoelectric effect in conjunction with the cells, which are
p-n diodes and are only micrometers in dimension. The photoelectric effect
promotes electrons from the valence band into the conduction band when the
photons interact with the crystalised silicon (Kuhn et al., 2014). The junction of
the semiconductor is sensitive also to radiation in the form of Beta particles and
Gamma rays. They cause a release of electrons by ionising the individual atoms
of the chip. These electrons are then captured by the CMOS sensor chip and
create a white pixel. Due to the lack of an intrinsic layer, the CMOS sensor has a
weaker sensitivity to Gamma radiation. Preventative measures are taken to
decrease the external ambient light from reaching the sensor by placing black
electrical tape over the lens. This makes the white pixels created by the gamma
rays hitting the lens visible to the user and it also prevents alpha particles from
being detected due to their low penetrating ability.
The “Radioactivity Counter “application acts as the software analysis tool which
visualizes the data from the sensor. The software is limited by the frame rate of
the smartphone (approx. 30 frames/second). In a designated time period, the
application records the sum total of the detected particles interacting with the
sensor. In the Application interface, the camera display is shown, and the
application alters the settings of the camera so that any black pixel changes into
a white pixel. (Bushberg and Boone, 2011)
The recorded measurements in this experiment where all evaluated and carried
out using this software analysis application with two different smartphone
camera devices, The Sony Xperia Go ST27i, and the Alcatel One Touch 903.
Figure 7. Phone lens covered Figure 8. CMOS Sensor

12. 7
Summary
With the increased popularity of smartphones and portable devices, there has
been a large growth in the number of applications which can be downloaded and
which provide a wide variety of functionalities and utilities. An application called
Radioactivity Counter, which is available commercially, claims that it allows for
the accurate detection of radiation dose to a user given in microGray per hour
(μGy/h) by implementing the camera of a smartphone. The camera is sensitive to
both visible light and also gamma photons, which are of a higher energy. The
application utilizes the sensitivity of the on Board complementary metal oxide
semiconductor (CMOS) sensor to detect the surrounding radiation levels. This
silicon-based sensor is present in most modern smartphone cameras. The CMOS
sensors are on-board small silicon chips, which are used in the device for the
detection of visible light. However the sensor also has the ability to detect
gamma radiation, which operates on a higher wavelength. The signal of the
ionising radiation, when compared to visible light, is undetectable because of the
small acquisition time of the image of approximately 100 milliseconds. This
means that the responses of the camera to the radiation are not normally shown
to the user. However by making a small configuration in the form of black
electrical tape, which is applied over the lens of the camera, it eliminates all of
the visible light. The response of the gamma rays hitting the sensor can now be
observed. The radiation counter application implements the phone cameras
ability to detect the gamma rays and records the number of times the sensor
detects the interactions. Once the device is calibrated, the phone can then
convert the recorded number of interactions into a dose rate per hour. This
project aims to design, test and understand this setup to determine its
effectiveness as a low cost gamma detector. (Gröber et al., 2014)
Aims
 To design a detector using a smartphone camera with CMOS sensor
 To compare the sensitivity of different phones
 To compare the efficiency of the detector to semiconductor detectors
 To see if the detector can be used as a dosimeter
Materials
Two Smartphones: Sony Xperia Go ST271, Alcatel One Touch 903
4 Gamma Sources: Am-241 (0.1μCi), Co-60 (1μCi), Cs-137 (1μCi), Ra-226 (5μCi).
Black Electrical tape
Ruler and Protractor
Retort Stand
Two Dosimeters: Mini Rad series 1000, Mini 6100 series EPD
Lead shielding
Thallium-activated NaI(TI) scintillation detectors 3”x3” well detector
905 Series Ortec Thallium-activated NaI(TI) scintillation detector
Amptek XR-100T-CdTe X-Ray & Gamma Ray Detector

13. 8
Method
Detector Application Design and layout
Figure 9. Software Analysis Application Layout
The upper right portion of the application displays the image of the camera. This
should be displaying black when covered with black tape. When the gamma rays
interact with the sensor chip, white pixels appear. The application only has the
ability to display a maximum value of 200 white ray pixels per image frame. This
can result in only part of the rays being displayed in the presence of a high
radiation field. If the lens cover is removed, then there will be a dramatic
increase in the number of white pixels measured by the software analysis tools.
A warning message is then displayed.
The number of Counts Per Minute is displayed on the upper left corner of the
application, and below it is the dose reading in μGy/h. This dose value changes
from a red to green colour once calibration is complete to define adjustments of
CPM values for corresponding μGy/h values. When the sensor experiences an
increase in the radiation field, this value is automatically adjusted to mGy/h or
Gy/h values respectively. When measuring the radiation dose, the value will turn
green after 5 minutes of values are recorded. [3]
The text values located below the timer each have a corresponding meaning.
“n” represents the noise value of the phone with values of units. The lower the
value the higher the sensitivity of the phone. An increase in one unit results in
approximately 10% decrease in sensitivity.
“e” represents the exposure time. This is only displayed if the value is changed
from the default value. The default value is 0. Increasing the exposure time
increases the sensitivity of the phone but also increases noise value.
“t(/5min)” represents the standard deviation over the last 5 minutes of
measurements. It displays values in minutes out of a total of 5 minutes e.g
t(3/5min). The higher the standard deviation percentage, the more stable the
radiation measurements in the current environment.
“fps” represents the frames per second. The higher the frame rate of the phone
implies an increase in phone sensitivity.
“t” represents the internal temperature of the device battery. An increase in the
temperature can results in an increase in noise. No temperature correction is
implemented in the algorithm of the applications software if the temperature
interferes with the sensitivity of the phone.

14. 9
The name of the phone is also displayed along with the Application program
interface level.
There are three buttons below the text values:
Stop log/Start log
A button, which can be toggled, is available once the noise value of the phone has
been defined. If a log is initiated, a test field appears and the name of the log file
can be entered. Once the log has been named, the software records the CPM
value as well as each corresponding text value including a temperature stamp.
These log files are stored on the phones internal memory/memory card and can
be accessed from the settings menu.
Clear button
The CPM values (the measurements recorded) are deleted and the device resets
the counts. The CPM values are red and turn green once 5 minutes of data has
been recorded once again.
Spect button (Spectrum button)
A bar chart or a spectrum can be displayed of the CPM in the lower right side of
the software display. The Spect button toggles between the two options. The
maximum amount of time, which can be displayed as a bar chart, is 60 minutes.
The Application Menu
The menu has a six available buttons.
Figure 10. Application Menu Options
Help button
This option displays a text option of a detailed user manual for the software
application.
Settings button
The settings option allows for a number of parameters to be adjusted.
Interval: the interpolation interval time for the spectrum display can be adjusted
in increments of 5, 10, 15 or 30 minutes.
Border: Increasing this value reduces sensitivity but it is useful for phones,
which have a high level of noise around the lens border.
Enable Alarm: An audible alarm can be set and displayed in the main software
interface.

15. 10
Figure 11. Application Settings Menu
Frontcam: this option is only available if the device has a front camera. It changes
the spectrum to be taken from the front lens and not the back camera. Front
lenses are more sensitivity to light, but they also have an increased noise value.
In cameras where the back lens sensor does not have a high sensitivity, the front
camera can be used instead if available.
Set noise button
This allows for the noise value to be recalibrated and determined.
Calc button
This is a unit converter. This allows for rough estimates between dose and
equivalent dose calculations. This allows for easy conversions and manipulation
of data result values by changing the units as need from Sievert, Gray, Curie or
Becquerel.
Figure 12. Application Calculation Converter

16. 11
Statistics Button
This menu option is where the data from the logged files is saved in bar chart
form of Counts Per Minute where each bar represents one minute of counts. The
logged file can be saved as a CSV or html file. It can also be emailed as a CSV file
attachment. There is also an option to delete the logged file. In the graph saved of
the logged file there are a number of options. The display can be changed from a
bar chart to a dot, lines notation. The logged file is stored every minute with the
automatic set noise (n) value as well as n+1 and n+2 values. This allows for
useable data to still be obtained if the camera sensor had an increase in noise
during the data acquisition process. The cpm0 (background radiation
determined) reading allows for the mean value of CPM to be automatically
adjusted to cancel out the CPM-noise of the background radiation from all future
counts.
Figure 13. Application Statistics Menu
Adjust button
This menu allows for up to four CPM values to be given corresponding dose
values in μGy/h. A dose curve shows the resulting data as a graph of μGy/h
versus Counts Per Minute. An alarm value can also be set here, which once the
alarm threshold has been reached, an audible sound and warning symbol will
occur. The CPM-noise value can also be adjusted here. The value is determined
on the measurements entered. If the value is too high, then the noise value
should be increased to lower the value. Repeat the process and if the values do
not match use the default CPM-noise value to calculated original value.
Figure 14. Application Adjust Menu

17. 12
Disclaimer: Two mobile phones are used in this setup and compared against
each other. They are the Sony Xperia Go (ST271) and the Alcatel One Touch
(OT – 903).
Calibration of Noise
The Lens of the camera must first be covered with black tape, so as not to allow
any light into the camera. To determine if the tape is effective at being totally
light dense the camera lens should then be placed in front of a light source, and
the number of counts should not increase. It the sensor registers additional
counts; this will decrease the accuracy of the phones readings as it is recording
false counts. To compensate the lens can be double or triple taped with or
without aluminum foil to block out the light. It is important to note that if the
phone has a front camera, then it too should be covered, as the application also
has the ability to measure counts using the front lens.
Figure 15. Phone Camera Lens covered with black tape
The Noise level of the phone must first be determined. The noise level varies
from phone to phone. It can range anywhere from values of 2-60. It is impossible
to cancel out the noise entirely, however the lower the noise value, the greater
the sensitivity of the phone. The noise value can be determined using the
calibration function. The function will measure the sensitivity of the sensor to
light and find a zero count rate in order to start accurate measurements. The
calibration takes approximately one minute. It is recommended that the phone
be surrounded in lead shielding during the set noise phase if the location has a
higher than normal background radiation.
Figure 16. Calibrating Noise Level

18. 13
Once the noise value has been set, the application will run a mean calibration for
a recommended 6-10 minutes. This allows for an accurate measurement of the
background zero count to be determined. The phone should produce an audible
click noise, which represents photons interacting with the sensor cell and being
recorded by the software tools. The counts of the white pixels carried out by the
application occur in segments of one minute. The displayed values are given in
units of Counts Per Minute (CPM). The application should be recording on
average a background radiation of 1-10 CPM.
Figure 17. Determining mean CPM calibration
If a phone is displaying a very high CPM this may be a result of a very high noise
value. The noise value can be decreased but with the loss of sensor sensitivity. If
the CPM is too low and no counts are being measured, the noise level should be
adjusted and increased in order that a reasonable background radiation level can
be obtained.
If there are white dots in a circle or elliptical pattern, then the lens cover may
need to be adjusted to make sure it is not allowing light to reach the sensor.
Retest by checking if there is an increase in CPM on front of a bright light source.
The filter can be changed in the filter settings; this allows an adjustment in the
size of the display spectrum. The exposure can also be lowered in the settings.
Background Counts (CPM -0)
Once the detector has been calibrated and the noise level determined, the phone
application is now ready to begin recording data. Before any measurements are
recorded, the CPM – 0 (Background Counts) of the phone should be recorded.
This allows for more accurate measurements to be taken later on of radiation
sources as the background CPM value can be taken away from the recorded
radiation source to obtain a true CPM reading.
The detector should be placed in the same position/location for the whole
experiment. In order to obtain an accurate CPM – 0 reading all radiation sources
and external sources should be removed from the detector area. The longer the
data is recorded for, the more accurate the Background counts will be. Therefor
the detector should be left running for approximately 10 hours. The mean counts
can then be obtained from the data and the CPM-0 can be implemented into the
adjust menu in the application. This takes the Background counts out of any
future recorded data.

19. 14
Testing Radiation Sources
A variety of different Gamma Radiation Sources are available including
Americium 241(Am–241), Cobalt 60(Co-60), Cesium 137(Cs-137) and Radium
226(Ra-226).
These sources are placed in front of the detector Camera lens/window. In order
to obtain accurate CPM mean value counts for each gamma source, the detector
must be used to measure each source over a long period of time (10 hours).
Using the software analysis application, the data can be sent to a computer in a
CSV file and converted to an .xlc file. This allows the data to then be plotted and
graphed in excel.
Obtaining Radiation dose of Sources
In order to calibrate the Phone camera detector to accurately measure dose, the
radiation sources must all have their dose levels determined. Two different
dosimeters are used to verify the dose readings, an analog counter- “Mini rad
1000 Series Monitor” [2] and a digital counter- “Mini 6100 series Electronic
Personal dosimeter (EPD).
Figure 18. Mini Rad series 1000 Figure 19. Mini 6100 series EPD
The Mini Rad has an x on either side of the measurement screen to represent the
detector window. The Mini 6100 has three circles to represent the detector
window. The devices have already been calibrated. The dose measurement is
given in μSV/hr values. Measurements should be taken by placing the different
radioactive sources at the detctor window and also at other positions of the
detcteor in order to gauge an acurate reading.
Dose Calibration of Detector
The ability of the Phone Camera detctor to acuratly detect a dose reading in
μSV/hr must be calibrated. The mean CPM values for each Radioactive source
over 10 hours is implemented with the mean dose reading recorded from both
the digital and analog dosimeters. These values are imputted into the adjust
menu in the software application settings menu. (refer to figure.) This allows for
a dose calibration curve to be obtained. Depending on the acuracy of the
imputted data, the Software should now give a μSV/hr dose reading at the
detector window. The CPM-0 value should also be recorded here to give a base
line cut off to cancel out the background radiation for a more acurate result.

20. 15
By taking each individual mean CPM for of the four radioactive sources, the value
for one CPM can be obtained for each source. Using these 4 values for one CPM. A
mean of all four values should be obtained. This value can them be used as the
standard 1 CPM value for calibration. This allows for higher values such as
1000μSV/hr to be estimated. The data can be exported to Excel and graphed and
plotted. A linear Plot of Counts vs. Dose(μSV/hr) should be obtained as in the
following Plots taken from the Software manufacterer’s website. The results
should be repeated and graphed for each Phone being tested.
Figure 20. Linear Plot Counts vs. Dose (μSV/hr)
Thermal Noise evaluation
The Software Application recordes the internal temperature(°C) of the phone for
every CPM value. In order to determine the effects of the temperature on the
CPM, there must be a large and substantial amount of data points recorded at
each temperature. The larger the number of data aqusition points collected for
each temperatuure, the greater the accuracy and reliability of the results. A least
100 minutes of data should be recorded for each temperature of the phone. The
temperature range depends on the internal scematics of the phone. It may be
difficult to obtain high temperatures due to the safety precautions which the
phone takes in order to maintain a safe internal temperaure. The temperature of
the phone increses by connecting it to a charging AC supply. The mean CPM
value at each temperature should be recorded. The data should them be
tabulated and graphed in excel in order to establish a signal noise realationship
betweem Temperature and Counts.
Investigation of Detector performance to the Inverse square Law
The investigation is carried out into the Camera detector to confirm to the law
that there is a realationship that exists between the decreses in radiation
intensity with an increase in distance due to the geometrical fact that the surface
of a sphere increases with distance squared (d2). This realationship can be
determined with a simple setup. A retort stand is used to hold a rdaioactive
source (Cs-137)in position. It is imperitive that the source is directly in line with
the camera detector window. This is to make sure acurate results are obtained,
as misallinment of the source can cause errors in the counts. The data CPM is
rcorded at a certain positional distance of the source to the detcetor e.g. 5cm.
This distance can then be incresed on equal incriments.It is important to note

21. 16
that the same number of counts should be recorded at each position and the
overal geometry position in the x and y plane should not change. The larger the
number of counts that are recorded, the more acurate the average data value will
be. The usuable distance range for the measurements of position (rmin,rmax) are
determined. rmin is obtained based on the fact that the usuable distance of
detection should be approximatly five times the diameter of the radiation source.
The sources are usually 5mm in diameter. The rmax value varies depending on the
detectors sensitivity which varies from phone to phone.
Absorption effects of the air is negligable as the electrons (0.546/2.2 MeV) have
a range of 1.5 -10m in air. These values are much higher than the usuable
detector range of the CMOS sensor detcetors.
Once the data has been obtained from the different positions, the data can be
exported to excel, tabulated and a graph of Counts vs 1/disance2 (1/d2) should
show a linear realationship through the origin. [6]
Investigation into Variation of Counts to the angle of detection
The Variation of the Count rate with respect to the angle of detection can be
investigated by having the detector in a fixed position. The angle of the
radioctive source being used (Cs-137) can be changed in increments of 10°.
However the distance of the source to the detector window must be fixed for all
measurements, and the source height must also be constant for all
measurements. Again by keeping all of these parameters unchanged for each
variable angle, and obtaining a reasonable amout of data points e.g. 100 Minutes
of CPM. Then an accurate realationship of the number of Counts detected to the
change in the angle of the source to the deetctor can be obtained and graphed.
Investigation into the effects of lead shielding on the count rate
The efects of lead (Pb) shielding can be examined on the count rate. The Detector
should be set up at a certain distance from the a chosen radioactive source
(Cs -137). The position of both should be fixed in position. Lead shileding should
then be positioned between the detector and the sourse. The lead shielding used
has a thickness of 3mm. A number of values are recorded for a constant amount
of time in order to obtain vallid accurate results. The cumulative thickness of the
lead shielding of the gamma source is increased in incriments of 0.3mm until a
total of 24mm. This data is then plotted in excel of counts vs. Cumulative Pb
thickness.
Determination of Dead time using the two source method
The dead/resolving time (τ) of a system can be obtained using the two source
method. Two different radioactive sources muct be used. The first step is to place
source 1(Cs-137) and source 2(Co-60) in combination together (m12) in front of
the deterctor window at a fixed distance. In order to obtain acurate results, all
data measurements must be carried out over a long period of time (10 hours),
this is because the sources will have similar counting rates. The next step is to
repeat the measurements seperatly with each source, source 1(m1) and source 2
(m2). However it is important to note that the sources must be kept in the same
position as they were when the combined position measurements were taken.
This allows for the solid angle to be preserved. The background counts (mb) for

22. 17
the same length of time must also be implemented in the following calculations
to obtain the resolving time of the camera phone detector.(Myers, 1956)
𝑋 = 𝑚1 𝑚2 − 𝑚 𝑏 𝑚12
𝑌 = 𝑚1 𝑚2 (𝑚12 + 𝑚 𝑏) − 𝑚 𝑏 𝑚12(𝑚1 + 𝑚2)
𝑍 =
𝑌(𝑚1 + 𝑚2 − 𝑚12 − 𝑚 𝑏)
𝑋2
𝜏 =
𝑋(1 − √1 − 𝑍)
𝑌
Comparing Detector efficiencies
Five detectors are compared in this investigation.
Two smartphone cameras running the “Radioactivity Counter” software
application and which have been calibrated using the previous methods.
Two Thallium-activated NaI(TI) scintillation detectors are also used. One is a
NaI(Ti) 3x3 well detector incased in a large metal casing. The other detector is
905 Series Ortec NaI(TI) scintillation detector. The Ortec detector is more hands
free and has a built in Photo Multiplier Tube (PMT) whereas the Well detector
requires an external PMT and a Multi Channel Analyser (MCA). Both detectors
use the Software analysis tool Maestro produced by Ortec.
The Final detector used is an Amptek XR-100T-CdTe X-Ray & Gamma Ray
Detector, which is thermoelectrically cooled X-ray detector and preamplifier
using CdTe diode. It uses its own Amptek Software analysis tools.
The Counts are measured for all of the detectors using the Co-60 and the Cs-137
sources for exactly 10 hours. The phones generate bar graphs, which must then
be exported into excel and graphed. The total counts can then be determined.
For the other four detectors, a photopeak is obtained for both sources. The
photopeak energy is then calibrated with the known energies of Cesium-137
(662KeV) and Cobalt-60 (1173 and 1332KeV). The total counts must be
recorded at the photopeak for each source. The absolute detector efficiency can
be obtained for each detector and compared as a percentage. The efficiency of a
detector is given by the ratio of number of particles detected/ number of
particles emitted. (Kadum and Dahmani, 2014)
𝜖 =
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠 𝑜𝑓 𝑟𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛 𝑑𝑒𝑡𝑒𝑐𝑡𝑒𝑑
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠 𝑜𝑓 𝑟𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛 𝑒𝑚𝑖𝑡𝑡𝑒𝑑
𝑋 100
There are a number of other important parameters, which are important when
comparing detectors such as, Efficiency Resolution, Intrinsic efficiency or Full
energy Peak efficiency. However the data from the Phone Camera detectors is
limited as it only gives Counts Per minute and not the Energies.

23. 18
Results
Noise Calibration and Determination of Background Counts:
Figure 21. Sensor Spectrum of the Sony Xperia Phone
This Spectrum represents the area of the Camera lens over which the most signal
is being recorded. The maximum value of noise, which is recorded by the
Application, is
n = 15.
Note: A Sensor Spectrum was also obtained for the Alcatel One Touch Phone. A
Noise value of n = 33 was recorded. Noise calibration cannot be exported to CSV
so Screenshot must be taken. Alcatel Phone has no Screenshot feature. But a
large noise peak was shown with maximum value centered on 28 with a highest
noise reading occurring at 33.
Figure 22.
Background
Count of
Sony Xperia
Phone
Figure 23.
Background
Count of
Alcatel
The Background counts were determined by running both the Sony Xperia
Phone and Alcatel One touch detectors without the presence of any radioactive
source over a period of 600 minutes (10 hours).
A mean value of the Background Radiation (CPM zero) of the Sony Xperia ST27i
phone was determined to be 4.51 CPM.
A mean value of the Background Radiation (CPM zero) of the Sony Xperia ST27i
phone was determined to be 20.73 CPM.
0
5
10
15
1
28
55
82
109
136
163
190
217
244
271
298
325
352
379
406
433
460
487
514
541
568
595
Counts
Time (minutes)
Background Sony 10 hours
0
10
20
30
40
50
60
1
28
55
82
109
136
163
190
217
244
271
298
325
352
379
406
433
460
487
514
541
568
595
Counts
Time (minutes)
Background Alcatel 10 hours

24. 19
Testing Radiation Sources
Figure 24.
CPM Sony
Phone for
Cs-137
source
Figure 25.
CPM
Alcatel
Phone for
Cs-137
source
Figure 26.
CPM Sony
Phone for
Co-60
source
Figure 27.
CPM
Alcatel
Phone for
C0-60
source
0
20
40
60
80
100
120
1
28
55
82
109
136
163
190
217
244
271
298
325
352
379
406
433
460
487
514
541
568
595
Counts
Time (Minutes)
Cesium-137 (sony)
0
200
400
600
800
1000
1
28
55
82
109
136
163
190
217
244
271
298
325
352
379
406
433
460
487
514
541
568
595
Counts
Time (Minutes)
Cesium-137 (Alcatel)
0
20
40
60
80
100
1
28
55
82
109
136
163
190
217
244
271
298
325
352
379
406
433
460
487
514
541
568
595
Counts
Time (Minutes)
Cobalt-60 (Sony)
0
100
200
300
400
500
600
700
1
28
55
82
109
136
163
190
217
244
271
298
325
352
379
406
433
460
487
514
541
568
595
Counts
Time (Minutes)
Cobalt-60 (Alcatel)

25. 20
Figure 28.
CPM Sony
Phone for
Am-241
source
Figure 29.
CPM
Alcatel
Phone for
Am-241
source
Figure 30.
CPM Sony
Phone for
Ra-226
source
Figure 31.
CPM
Alcatel
Phone for
Ra-226
source
0
5
10
15
20
25
30
35 1
26
51
76
101
126
151
176
201
226
251
276
301
326
351
376
401
426
451
476
501
526
551
576
Counts
Time (Minutes)
Americium-241 (Sony)
0
200
400
600
800
1
28
55
82
109
136
163
190
217
244
271
298
325
352
379
406
433
460
487
514
541
568
595
Counts
Time (Minutes)
Radium-226 (Sony)
0
1000
2000
3000
4000
5000
6000
1
28
55
82
109
136
163
190
217
244
271
298
325
352
379
406
433
460
487
514
541
568
595
Counts
Time (Minutes)
Radium-226 (Alcatel)
0
100
200
300
400
1
28
55
82
109
136
163
190
217
244
271
298
325
352
379
406
433
460
487
514
541
568
595
Counts
Time (Minutes)
Americium-241 (Alcatel)

26. 21
Obtaining Radiation dose of Sources
Source Sony Mean CPM Alcatel Mean CPM
Analog Dose
(μSv/hr)
Digital Dose
(μSv/hr)
Background 4.51 20.73 NA NA
Am-241 21.62 177.49 0.55 1
Co-60 39.61 285.5 14.5 17
Cs-137 42.42 469.7 19 21
Ra-226 545.18 3773 100 105
Figure 32. Radiation Dose values determined of each Source
Dose Calibration of Detector
Figure 33. Calibration Dose Linear Curve For Sony and Alcatel Phones
1
10
100
1000
10000
100000
1000000
10000000
100000000
0.1 1 10 100 1000 10000 100000 1000000
Counts
μSV/hr
Calibration Curve
Sony
Alcatel

27. 22
Thermal Noise evaluation
Figure 34. Thermal Noise in Sony Phone
Figure 35. Thermal Noise in Alcatel Phone
0
10
20
30
40
50
60
31 32 33 34 35 36 37 38 39 40 41 42 43 44
Counts
Tenperature (Celcius)
Sony Temperature 100 Counts
440
450
460
470
480
490
500
510
28 29 30 31 32 33
Counts
Temperature (Celcius)
Alcatel Temperature 100 Counts

28. 23
Investigation of Detector performance to the Inverse square Law
Figure 36.
Counts vs.
Distance
Sony
Phone
Figure 37.
Counts vs.
Distance
Alcatel
Phone
Figure 38.
Counts vs.
1/d2 Sony
Phone
Figure 39.
Counts vs.
1/d2
Alcatel
Phone
0
10
20
30
40
50
0 1 2 3 4 5 6
Counts
Distance (cm)
Cesium-137 Sony 100 Counts
0
10
20
30
40
0 0.2 0.4 0.6 0.8 1 1.2
Counts
1/(distance)^2
Sony Counts vs 1/Distance^2
0
100
200
300
400
0 0.05 0.1 0.15 0.2 0.25
Counts
1/(distance)^2
Alcatel Counts vs 1/Distance^2
0
100
200
300
400
500
600
0 5 10 15 20 25 30
Counts
Distance (cm)
Cesium-137 Alcatel 100 counts

29. 24
Investigation into Variation of Counts to the angle of detection
Figure 40.
Counts Vs. Angle
Variation Sony
Phone
Figure 41.
Counts Vs. Angle
Variation
Alcatel Phone
Investigation into the effects of lead shielding on the count rate
Figure 42. Counts
Vs. cumulated Pb
Shielding Sony
Phone
Figure 43. Counts
Vs. cumulated Pb
Shielding Alcatel
Phone
0
100
200
300
400
0 20 40 60 80 100
Counts
Angle(° )
Alcatel Angle Variation 1cm
0
10
20
30
40
0 20 40 60 80 100
Counts
Angle(° )
Sony Angle Variation 1cm
0
10
20
30
40
50
0 5 10 15 20 25 30
Counts
Cumulative Pb Shielding
Lead Shielding Sony (Cs-137)
10mins
0
100
200
300
400
0 5 10 15 20 25 30
Counts
Cumulative Pb Shielding
Lead Shielding Alcatel (Cs-
137) 10mins

30. 25
Determination of Dead time using the two source method
Detector M1 (CPM) M2 (CPM)
M12
(CPM)
Mb
(CPM)2
Alcatel 342 388.2 518.4 20.73
Sony 28.22 22.89 34.75 4.51
Figure 44. Two source method results (CPM)
Detector M1 (CPS) M2 (CPS) M12 (CPS) Mb (CPS)
Alcatel 5.7 6.47 8.64 0.346
Sony 0.47 0.382 0.58 0.076
Figure 45. Two source method results (CPS)
Detector X Y Z
τ
(seconds)
Alcatel 33.889 295.013 0.818 0.065
Sony 0.135 0.08 0.857 1.049
Figure 46. Detector calculated Dead/Resolving times.
Comparing Detector efficiencies
Detector Cs-137 Counts Total Cobalt-60 Counts Total
NAI(TI) Well 2076569 248775
NaI(TI) 873439 103085
CdTe 191897 20383
Alcatel 281829 171279
Sony 25451 23766
Figure 47. Detector Counts Comparison
Detector Cs-137 Decays/Second Co-60 Decays/second
NAI(TI) Well 57.68247222 6.910416667
NaI(TI) 24.26219444 2.863472222
CdTe 5.330472222 0.566194444
Alcatel 7.828583333 4.75775
Sony 0.706972222 0.660166667
Figure 48. Detector Decays/second Comparison
Detector Efficiency (%)
NAI(TI) Well 14
NaI(TI) 10
CdTe 3
Alcatel 1.215
Sony 0.104
Figure 49. Detector Efficiencies

31. 26
Figure 50. NAI(TI) Well Cs-137 Figure 51. NAI(TI) Well Co-60
Figure 52. NAI(TI) Cs-137 Figure 53. NAI(TI) Co-60
Figure 54. CdTe Cs-137 Figure 55. CdTe Co-60

32. 27
Discussion
A gamma detector using two smartphone cameras to detect high-energy photons
being released by radioactive gamma sources was successfully designed and
tested following the above method preciously. The noise calibration of both
devices revealed that the noise value can and does fluctuate for each phone. This
noise value is determined by the phone manufacturer’s internal design and setup
of the device. The Alcatel phone registered a noise value of over double that of
the Sony phone, indicating that it is more sensitive but also more susceptible to
signal noise.
The Background CPM-0 counts were found for both phones. The results revealed
that the added noise value in the Alcatel phone caused it to be more sensitive to
photons and detect more counts than the Sony phone. The Alcatel phone
recorded five times the Counts. The phone detectors were tested with a variety
of sources and showed that they have the resolution ability to differentiate
between different sources by producing different CPM mean values for each with
increased CPM for sources with a higher activity consistent with detector theory.
It should be noted that the Alcatel phone had between 5 and 11 times more
counts than the Sony phone depending on the source being tested.
By recording the dose rates of each of the four sources on both an analog and
digital dosimeter, accurate values of dose rate values were found. These values
were then implemented with the corresponding CPM mean values to create a
calibration dose curve. The values above 100μSv/hr were estimated based on an
average value for 1 CPM. The graph of counts verses dose revealed a linear
relationship between counts and dose for both phones. As the Dose rate
increases, the counts directly proportionally increase. The Alcatel had higher
count values than the Sony phone, however despite the higher noise value it has,
it still produces count dose linearity. These results are consistent with the dose
calibration curves, which were carried out by the manufacturer for a wide
variety of phone model.
An examination was carried out into the effects thermal noise has on the count
rate. Both phones were set up with a Cs-137 source for the course of several
days. One hundred data points were recorded at each temperature. The results
showed a relationship between the counts and the degrees Celsius. As the
temperature is increased, the count rate also increases. Some of the values
decrease but it is assumed that by obtaining a greater number of data points to
use as the baseline measurements, that a more consistent graph would be
obtained with counts increasing exactly proportional to the temperature rise.
This noise effect was observed in both phones. However it was noted that the
Sony phone operated on a much higher and wider temperature scale. This could
be as a result of the phone battery being integrated and non removable in the
phone, unlike the Alcatel phone, which uses a removable battery. Therefore the
temperature of the battery could have a greater effect on the noise on the counts
of the Sony phone, but the Sony phone has a smaller noise value and count rate
than the Alcatel phone. This could be because the Sony phone is more expensive
and modern and may have failsafe procedures built into the system coding
architecture to decrease the effect signal thermal signal noise has on the phone.

33. 28
As part of testing the performance of the Gamma camera, an investigation was
conducted into a wide variety of gamma radiation properties under detectors.
This properties and results did not differ overall from expected results based on
data collected for other types of detectors and the theory behind the
relationships.
An investigation was carried out to determine the effects of distance on the count
rate of the gamma camera. The setup and procedure was followed and the
results were tabulated and graphed. It was found that the results verified the
Inverse Square Law for both phone detectors. When a graph was created of
counts versus the distance of the source to the detector window, it was found
that there was an exponential decrease in the number of counts recorded as the
distance was increased. When the distance was doubled the count intensity was
decreased approximately by (1/d2). A graph was plotted of Counts vs. 1/d2. This
showed a straight-line graph. This clarifies the relationship that as the counts are
increased then the corresponding 1/(d2) values also increase and are directly
proportional to each other. It was found that the Alcatel phone had a detection
range of five times that of the Sony phone. This shows that it has a greater
sensitivity range and again shows that the Alcatel phone is more susceptible to
the photons.
An investigation was carried out into the detectors performance to a change in
the angle of the source the detector window. The setup was followed according
to the method, and a graph for both phone gamma cameras were obtained. They
showed consistent results. As the angle was increased, the count rate decreased
exponentially. This shows the importance of the source position with respect to
the lens window in order to obtain accurate results. Both phones showed that at
approximately 40° the CMOS sensor could no longer detect high-energy
penetrating photons from the camera and only recorded CPM-0 background
radiation.
An investigation was carried out into the effects of increased lead shielding on
the counts recorded of gamma sources. The procedure was followed as in the
method. The lead shielding was increased in increments of 0.3mm. The results
were plotted and graphed and showed that there is an exponential decrease in
counts recorded by the gamma phone as the lead shielding is increased. The half
thickness value recorded which reduced the count rate by half was 8.2mm The
values were recorded for periods of 10 minutes at each shielding measurement
thickness. The expected half thickness of lead is 5mm. This large error in the
result of the half thickness could be improved by running the measurement for
longer periods of time to obtain a more consistent exponential curve.
Using the two-source method with Cs-137 and Co-60 sources and measured
background radiation, the resolving/dead time was calculated using the
formulas found in the method. A resolving time of the detector is the interval of
time until the detector can record another event. In order to obtain accurate
detector results, a small dead time is required. The dead time for the Sony phone
was 1.05 seconds. This is not a particularly good result as a Geiger molar counter
has a dead time in the region of microseconds (μs). The dead time was recorded
for the Alcatel detector to be 65milliseconds (mS). It would be assumed that the
detector dead time should be approx. the same for similar detector system such
as a CMOS sensor detector. The low dead time recorded for the Sony phone could
be as a result of inconstant data with high variations in recorded results.

34. 29
Finally the absolute efficiency of the gamma detectors were compared to that of
a variety of more sophisticated and different gamma detectors. The efficiency of
the recorded photons/second for the phones was very small in comparison to
the NaI(TI) detectors in both the well and stand-alone detector. The Cadmium
Telluride detector had a very low absolute efficiency value due to the energy
specificity of the detector. As the energy of the source (KeV) is increased the total
efficiency decreases. The efficiency of the Alcatel Phone was very high. This again
may be due to the over sensitivity to noise when compared to the Sony gamma
detector.
Conclusion
A low cost Gamma detector can successfully be designed through a simple
manipulation by covering the lens with a black tape. This setup can measure
high-energy photons, which penetrate the tape and are detected by the CMOS
sensor in the Phone. It is an unconventional application for a Smartphone to
measure radiation, however it can be implemented to provide qualitative proof
of ionising radiation. The device is limited as it cannot measure the energy of a
source, so the source cannot be identified, but once the device has been
calibrated, it can provide a reasonable measurement the surrounding radiation
field dose rate. Dose rates measured are quite accurate but not for sources under
10μSv/hr. and for determining the background radiation approx. 0.15μSv/hr.
This is due to the gamma phone detectors lower sensitivity when compared to
that of professional semiconductor detectors and Geiger counters. The
sensitivity varies greatly from phone to phone. The Alcatel phone detected over
10 times the number of counts in comparison to the Sony phone. This is due to
the detector’s internal setup such as CMOS sensor area, phone pixels, noise
interference and current leakage. However despite this, the phones detected
gamma radiation and also followed a number of pre-established theories
regarding the detection of gamma rays such as- the inverse square law and the
law of absorption. A number of factors affect the intensity of the counts and
cause noise such as the internal temperature. Also the phone is limited by the
geometrical position of the source to the detector lens.
There are many detectors, which provide greater efficiencies and more accurate
gamma detection. However the cost of these detectors range in the thousands.
The prevalence of Smartphones in the modern era is widespread. This Phone
gamma detector has a future in the detection of radiation. The number of
detectors is limited, and by simple manipulation and use of the software analysis
application, a smartphone can be turned into a useable gamma detector. It may
not be the most accurate or sensitive but it is the most widespread. In conclusion
the Phone detector has proved that it is a useable, reasonably accurate, low cost
gamma detector.

35. 30
Limitations
There are a wide variety of limitations associated with this phone camera
detector. The sensitivity of the gamma detector varies from phone to phone.
In order to obtain accurate results, the detector needs to be run for long periods
of time. This limitation poses an array of limitations; such as the battery power
length of the phone runs out quickly when using the software. This means that
the software can be run at night but will shut down after only a few hours
running. The radiation sources used must be handled with care. The sources
cannot be brought outside of the laboratory space. Therefore this means that
time management is crucial to obtain all of the data required in the limited time
available. To stop the detector from losing power and cutting off detections, the
phone can be left charging to an AC power supply. However this usage must be
limited as charging increases the internal temperature of the phones battery,
resulting in thermal noise and increase inaccuracies in the data values obtained.
Due to the time cost of a smartphone capable of running the software, there is a
limited availability to the number of smartphones, which can be measured. In
this experiment another phone (Alcatel) was purchased.
Finally the phone is limited with respect to the inability to determine the energy
of sources. When comparing the detector to other semiconductors, which are
able to detect energy, then this limits the variety and amount of efficiency
calculations, which may be carried out.
The activity of sources that can be used in this experiment is limited. The highest
activity was the Ra-226, which had an activity of 5μCi. Using sources any
stronger could result in damaging the CMOS sensor and leaving a permanent
“black spot” on the detector lens.
Recommendations
In order to improve this experimental investigation the number of smartphone
devices used to implement the gamma detector should be increased. This will
give a greater field of information on noise and count intensity. Also phones with
a front camera could be recorded and the sensitivity and noise of the radiation
intensity compared.
The number of radioactive gamma sources could also be increased. This would
allow for a more accurate calibration dose curve to be obtained, as it is lacking
linearity from 0-10μSv/hr.
If the experiment were repeated, a Geiger molar counter would also be used as a
comparison for each data value investigation routine. The smartphone detector
is effectively a Geiger molar counter and cannot be used to measure energy; this
limits the efficiency calculations in comparison to semiconductor detectors.
However direct counting comparisons can be made to a Geiger molar counter
and this would improve the quality of the analysis.

36. 31
References
Papers
BLOOR, E. F. 2013. Developing Methods to Measure Small Attenuation
Coefficients Using Short Distance Radiation Detection.
BUSHBERG, J. T. & BOONE, J. M. 2011. The essential physics of medical imaging,
Lippincott Williams & Wilkins.
GILMORE, G. 2011. Practical gamma-ray spectroscopy, John Wiley & Sons.
GRÖBER, S., MOLZ, A. & KUHN, J. 2014. Using smartphones and tablet PCs for β−-
spectroscopy in an educational experimental setup. European Journal of Physics,
35, 065001.
KADUM, A. & DAHMANI, B. 2014. Efficiency Calculation Of Nai (Tl) 2x2 Well
Detector.
KNOLL, G. F. 2010. Radiation detection and measurement, John Wiley & Sons.
KUHN, J., MOLZ, A., GRÖBER, S. & FRÜBIS, J. 2014. iRadioactivity—Possibilities
and Limitations for Using Smartphones and Tablet PCs as Radioactive Counters.
The Physics Teacher, 52, 351-356.
LILLEY, J. 2013. Nuclear physics: principles and applications, John Wiley & Sons.
MYERS, R. T. 1956. Dead time of a Geiger-Mueller tube by the double-source
method. Journal of Chemical Education, 33, 395.
SIEGBAHN, K. 2012. Alpha-, beta-and gamma-ray spectroscopy, Elsevier.
SPIERS, F. 1941. Inverse square law errors in gamma-ray dose measurements.
The British Journal of Radiology, 14, 147-156.
WAHLSTRÖM, B. 1995. Understanding radiation, Medical Physics Publishing
Corporation.

37. 32
Manuals
[1] 905 Series-Ortec
www.ortec-online.com/download/905-series.pdf (Accessed April 2015)
[2] Series 1000 'Mini Rad'
http://rp-alba.com/index.php?filename=MR1000.php (Accessed April 2015)
[3] Radioactivity Counter Application
http://www.hotray-info.de/html/radioa_help.html (Accessed January 2015)
[4] XR-100T-CdTe X-Ray & Gamma Ray Detector
http://www.amptek.com/products/xr-100t-cdte-x-ray-and-gamma-ray-
detector/ (Accessed April 2015)
Documents
[5] Alpha Beta and Gamma Radiation Lab- Northwestern University
http://courses.physics.northwestern.edu/new335/PDF/alphabeta.pdf
(Accessed April 2015)
[6] Ortec Geiger Counting
http://www3.nd.edu/~wzech/Application-Note-AN34-Experiments-Nuclear-
Science-Experiment-2.pdf (Accessed April 2015)
Images
[7] Radiation
http://physics.tutorcircle.com/waves/gamma-decay.html (Accessed April 2015)
[8] Compton Scattering
http://www.fesaus.org/glossary/lib/exe/fetch.php?media=terms:glsp22f1.gif
(Accessed April 2015)
[9] Pair Production and annihilation
http://electrons.wikidot.com/pair-production-and-annihilation (Accessed April
2015)
[10] Photoelectric effect
http://drgstoothpix.com/wp-content/uploads/2012/10/photoelectric-effect-
1.jpg (Accessed 2015)
[11] Inverse Square law
http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/invsqs.html (Accessed
April 2015)

38. 33
Appendix
Fig 56. Example Americium-241 interaction with CMOS
Fig 56. Example Cobalt-60 interaction with CMOS
Fig 56. Example Cesium-137 interaction with CMOS
Fig 56. Example Radium-226 interaction with CMOS

39. 34
Fig 57. NaI(TI) detector
Fig 58. NaI(TI) well detector
Fig 59. CdTe detector
Fig 60. Detector window of mini rad digital dosimeter

40. 35
Fig 60. Americium-241 Source
Fig 61. Cobalt 60 Source
Fig 62. Cesium-137 Source
Fig 63. Radium-226 Source

41. 36
Fig 64. Phone gamma detector setup
Fig 65. Phone gamma detector setup (Angle variation)
no date time cpm cpm n+1 cpm n+2
1 02/16/2015 16:49:54 71 29 13
2 02/16/2015 16:50:55 37 10 3
3 02/16/2015 16:51:56 45 26 12
4 02/16/2015 16:52:57 30 12 4
5 02/16/2015 16:53:58 28 10 3
6 02/16/2015 16:54:59 59 25 4
7 02/16/2015 16:56:00 47 22 8
8 02/16/2015 16:57:01 50 20 9
9 02/16/2015 16:58:02 71 19 2
uG/h mean(5) cpm mean(5) stddev (%) deg C
22.5 71 0 39
17.1 54 63 40
16.2 51 37.7 39
14.5 45.8 55.8 39
13.3 42.2 55.9 39
12.6 39.8 62.6 39
13.2 41.8 33.8 40
13.5 42.8 36.5 39
16.2 51 53.8 39
Fig 66. Example Raw data for Cesium-137 (Sony)