The Application implements a high energy photon detector for Gamma and X-Ray radiation sources.
Additionally a Mac OSX Application wich uses the built-in iSight WebCam of the MacBook Pro to detect high energy photons can be downloaded here.
The screenshot shows an active measurement where the logged EPM/PEM values of the 7th row indicate an event of high energy photon detection
Version 1.1 Changes:
The EVT Counter has been added which displays the High Energy Photon Events autodetected by the App [(EPM-Threshold) ≥ 10 and (PEM-Threshold) ≥ 20]. The resolution is limited to 1 event per minute.
The application uses the CMOS Image Sensor of the iPhone 4/4s front camera to detect high energy photons generated by X-Ray or Gamma radiation sources.
Radiation measurements are presented as relative values. The image sensor is not a calibrated device to detect ionizing radiation in a perfectly reproduceable way which prevents absolute measurements in Gray (Gy) or dose equivalent in Sievert (Sv).
SETUP & STEPS FOR MEASURING:
1.) IMPORTANT: Make sure that visible light cannot hit the sensor by obscuring the camera lens, e.g. with a piece of black tape. The Sensor View needs to be completely dark and should merely show some noise.
2.) Place the device in a low radiation environment. The app needs to be in the foreground with an active display to be in measurement mode.
3.) Adjust the threshold slider to a value which sets the reading of the CPM to around 1-5 Counts Per Minute without a detected high energy photon. It is important that the threshold isn't set too low because the sensor noise could render the measurement results unusable. If the threshold is to high then the detector looses sensitivity.
4.) The image sensor noise depends on its temperature which implies that the threshold needs to be adapted accordingly.
5.) Position the device near to a radiation source to be measured.
6.) Because of the small size of the CMOS-Sensor it can take some time until a high energy photon hits the sensor. Plan for a longer measurement (several minutes) to detect weak radiation sources.
7.) Analyze the logged data by checking the CPM (Counts Per Minute), EPM (Average Energy Per Minute) and PEM (Peak Energy Per Minute) to identify radiation events. The application autodetects probable events and indicates them by a "+" sign in the log view.
All readings are relative values by intention because the system isn't calibrated and consistent enough to calculate absolute values.
EVT - High Energy Photon Events autodetected by the App [(EPM-Threshold) ≥ 10 and (PEM-Threshold) ≥ 20]. The resolution is limited to 1 event per minute.
CNT - This is the overall count of activated sensor pixels. Even one high energy photon can activate several pixels which means that there is no direct correlation with the amount of X-Ray or Gamma photons hitting the sensor.
CPM - Counts Per Minute.
EPM - Average Energy Per Minute of the photons hitting the sensor during the measurement cycle. A reading significantly higher (delta ≥ 10) than the threshold value identifies most likely a high energy photon event. EPM readings near the threshold indicate normal sensor noise.
PEM - Peak Energy Per Minute represents the highest value detected by the sensor within the last measurement cycle. A significant threshold delta (≥ 20) identifies an event which will be logged if the EPM criteria is fulfilled.
MCY - The Measurement Cycle is shown by a count down.
Detector Physics & Limitations:
A semiconductor like the CMOS-Sensor in a camera is not just sensitive to photons of visible light but also to high energy photons of X-Ray and Gamma radiation. The picture below shows the Electromagnetic Spectrum and the associated wavelength/frequency of X-Ray and Gamma photons.
The other categories of radioactive radiation namely Alpha [α] (helium nucleus) and Beta [β] (electron / positron) particles cannot be detected because of the material in front of the camera sensor which mostly absorbs them.
A photon will be detected as soon as it reaches and gets absorbed by the sensor. If the energy is to high then the photon passes the sensor without any impact whereas a low energy photon probably doesn't reach the image sensor at all or gets mask by the sensor noise.
Example Measurements comparing environmental natural radiation with a weak radioactive mineral:
Environmental Measurement (4 Events of cosmic rays, natural Radon, etc.): |
Time: CNT: EPM/PEM: EVT:
| Weak radioactive mineral directly positioned above the camera lens (20 Events):
Time: CNT: EPM/PEM: EVT: