Abstract
The CMOS (Complementary Metal Oxide Semiconductor) image sensor of a smartphone has been known for its sensitivity to gamma-rays. In this research, some smartphones were selected and tested for measurement of gamma-rays emitted from Cesium-137 and Iridium-192 sources. During measurements, the phones were set in video mode while the camera lenses were covered with black adhesive tape to prevent light exposure. Interaction of gamma-rays with the CMOS appeared as flashing bright spots on the image. The bright spots were then counted by using the freely available ImageJ software. Preliminary results indicated that the number of bright spots increased linearly with increase of gamma-ray dose rate. An in-house Android application software was then developed for real-time counting of the bright spots. The application software also allowed users to input a calibration equation so that the phones could simultaneously convert the count rate to display in dose rate. This research demonstrated that, after appropriate calibration, smartphones could be used as gamma-ray measuring devices for radiation safety control involving high activity sources such as in industrial radiography, gamma-ray irradiation facility and medical treatment.
Highlights
Gamma rays have been extensively used in medicine, industry, agriculture, education and research
It could be clearly noticed that number of the bright spots increased with the dose rate
When the camera lens was covered with black adhesive tape, interaction of gamma-rays with CMOS chip caused flashing bright spots on dark background which could be counted with appropriate software to obtain count rate as in radiation counters
Summary
Gamma rays have been extensively used in medicine, industry, agriculture, education and research. Gamma-rays are electromagnetic radiation like visible light but they have energy approximately 104 to 106 times higher than that of the visible light. They can penetrate matter making them very useful in various ways. For better radiation safety control, the dose rate of 10 microsievert per hour (μSV/hr) is limited so that working totally 2000 hours per year (8 hours a day, 5 days a week for 50 weeks) will not exceed the annual dose limit of 20 mSv. Radiation workers must wear personal dosimeter like film badges which are completely replaced by thermoluminescent dosimeters (TLD’s) and more recently optically stimulated luminescent dosimeters (OSL’s) for measurement of cumulative dose from 1 month up to 3 months. Dosimeters for short term measurement are required such as digital personal dosimeter and survey meters which are not available for all workers
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