EBT3-based solar ultraviolet dosimeter

Abstract

This paper presents the development of a 10-bit Gafchromic external beam therapy 3 (EBT3)-based solar ultraviolet (UV) dosimeter that comprised only a single red light-emitting diode (LED) with a peak emission wavelength at 635 nm as the illumination light source and a photodiode as the detector. The color changes of EBT3 film have been previously proven to have a good relationship with solar UV exposure (in mJ/cm2). The newly developed dosimeter determines the solar UV dose by quantifying the discoloration of EBT3 film. In this experiment, the maximum accumulative dose by EBT3 film was recorded at 32,802 mJ/cm2. Segmentation technique was introduced on the nonlinear relationship between UV dose and the color changes of the films, which was represented by the output of the photodetector. Algorithm developed based on three segments produced the best calibration accuracy and was installed in the microcontroller prior to the measurement of the films. The calibration result produced by the EBT3 UV dosimeter managed to generate high coefficient of determination, R 2 = 0.9954 with root mean square error (RMSEC) of 657 mJ/cm2. The dosimeter also managed to produce high prediction accuracy with R 2 = 0.9963 and RMSEP = 471 mJ/cm2. The reproducibility results conducted based on 154 tests, on the other hand, produces R 2 = 0.9962 with RMSE 566 mJ/cm2.