Smartphones as dosimeters

Posted on 6th Sep 2017

Smartphone

Smartphone as a dosimeter

Disclaimer: The post below describes the ability of smartphones to measure radiation. Even though I would like to encourage everyone to try this out, you should be fully aware of the limitations and pitfalls in order to prevent any unnecessary worries.

My actual thesis is 15.000 words and should be revised before I want to post it. Due to time and financial constraint I decided to post a short version. I will follow this up with a post about how it actually works.

Run-up to thesis

When our kids where about one and two years old we had some very short evenings, like many parents have. During one of these nights I decided to start looking on PubMED (a research database) to see if I could find some light reading, like many parents do I imagine. During this search I came across an article by Joshua Cogliati (available online) and I was fascinated by this.

Not long after two students came to me searching for a subject to do their bachelor thesis on and I decided pitch smartphones as a dosimeter. Both students where fascinated and after some work we came to an agreement with an hospital nearby where they could measure the activity of several nuclear isotopes and compare those measurements to professional equipment. The results weren’t that great but they proved that even the apps available in de Google Play Store have basic potential.

Some colleagues were starting to notice the possibility as well so I was asked to follow this up with a short term research during Optimax 2015 (a summer school which took place in the summer of 2015 in Groningen). As a tutor I was blessed with an extremely motivated group of students and the results were quite intriguing and actually showed some potential when measuring nuclear isotopes.

I was geeking out!

Actual thesis (in short)

It should be clear by now that I had no other choice than to target this subject with my master thesis. Over a period of several months I started laying a basis and decided to focus on testing the reliability (how well repeated measurements are alike) and accuracy (how well do the measurements represent the actual dose rate) of smartphones as dosimeters with the aid of an application. As the applicability of smartphones to measure isotopes was already thoroughly tested by many others I decided to focus on testing it scatter x-rays in a fluoroscopy setting.

The biggest differences between previous research and my thesis were the dose rate and the average energy which is used in fluoroscopy. The dose rate difference roughly a fraction 8000 higher while the energy is roughly 1/6th during fluoroscopy.

Because of these differences I was interested in several points:

Different smartphone models are likely to contain different camera sensors. The size and surface of the sensors are of influence as well as the position of the sensor. This might influence the detection of radiation even though the same sensor is used in different models. For this purpose, several smartphone models were tested and compared.

Several apps were included to assess the differences and the effect of the user side calibration and conversion factors.

The penetration of radiation is influenced by its energy affecting the absorption. Even though the energy spectrum of scatter radiation is relatively low it might be of influence on the measurements, especially because of the limited thickness of de camera sensors. All measurements were performed using different tube voltages, thus creating a different scatter radiation energy spectrum.

The amount of counts influences the reliability of radiation measurements which in turn could lead to a decreased accuracy. As radiation doses vary with every fluoroscopy examination and position of the professional this could hinder the practical implementation of smartphones as dosimeters, for this reason three different dose rates were included.

As shown by Cogliaty et al., directional sensitivity of smartphones has an influence in detecting radiation from radioactive isotopes. Seeing as the energy from scatter radiation is lower, absorption will play a bigger role. Thus the angle of the smartphone in regard to the source could have an impact on the measurements. Additionally, the smartphone design itself might have an impact on the directional sensitivity causing differences between smartphones. Therefore a second set of measurements was performed to access the directional sensitivity.

Smartphones (table 1) were borrowed from family and friends, the apps (table 2) were bought from Google Play Store.

 

Table 1: Smartphones used

Smartphone

Series number

HTC Desire 500

SH38SWE02601

LG G2

LG-D802

LG G3

LG-D855

Samsung Galaxy S4

GT-I9506

Samsung Galaxy S3 mini

GT-I8190

 

 

Table 2: Apps used

App

Price (eu)

Developer

Version

GammaGuard

Free

Enviromental Instruments Canada

3.0.3

RadioactivityCounter

± 3,50

Rolf-Dieter Klein

1.8

GammaPix

± 3,50

Image Insight Inc.

3.0.15

 

In order to answer the sub-questions I used a fluoroscopy device and build a setup with a stack of Perspex as a scatter source. Measurements were performed at three distances (50, 100 and 150 cm) to create different dose rates. At each distance three energies were used. All measurements were repeated in fivefold this resulted in 765 measurements for each smartphone/app combinations and professional equipment used to verify the measurements. To test the directional sensitivity measurements were performed under different angles towards the Perspex stack as shown in figure 1 again in fivefold, this resulted in an additional 651 measurements.

Smartphone

Figure 1: Schematic top down view of the phone angles (blue) towards the Perspex stack (orange).

 

I shall be honest, the results quite surprised me! After calibration the accuracy had a roughly 10 % deviation from the golden standard (the professional equipment). This might sound like much but under optimal circumstances the deviation was mostly lower than 5 %. Keeping in mind this a measurement performed using a smartphone and app compared to professional equipment of several thousands of euro’s! Alongside the, in my eyes, impressive accuracy rarely was over 5 %.

There were minimal differences between smartphones and apps when looking at the dose rate and energy. However, these differences had a minimal effect.

A major drawback came in the form of the directional sensitivity. When turning the smartphone away from the source the dose rate was quickly reduces by roughly 50 % as shown in figure 2.

Smartphone

Figure 2: Directional sensitivity shown as a percentage from the 0o measurement.

In short, the results surprised me. I am convinced smartphones can be used to increase radiation awareness as done by others by using Philips Dose Aware. The professional doing this should however be fully aware of the drawbacks and be able to understand the measurements shown. Misuse could lead to a false sense of security or unnecessary worries.

Even though I focussed on a fluoroscopy setting these findings could be transferred to other situations. I used smartphones during practical lessons and lectures and have witnessed an increased attention under my students, it seems I am not the only one geeking out over this. In addition to this it might be worth looking in to applying this knowledge to situations were expensive radiation detection devices are not at hand. One could think about developing countries or first responders at a (possible) nuclear incident in order to make a quick risk assessment.

In all cases the drawbacks should be kept in mind and, without further research, smartphones should not replace professional equipment.