Characterising Silicon Diode response for radiation measurements

Abstract

X-ray radiation has been used in the treatment of cancer since its discovery in 1895. It was found that incorrect use of x-radiation can cause irreversible damage. It was necessary to introduce diode in-vivo dosimetry for x-radiation measurement to control the dose administered to patients. This study focuses on the characteristics of a p-type silicon diode as an x-radiation detector. The investigation involved measurement of the response of the diode under different conditions, which include gantry angle, field size, source to surface distance, off axis and wedge angle, in order to determine the optimum position for diode placement for both flat and curved surface. These conditions were varied and the corresponding change in response of the diode noted. The measurements were done on both the flat and curved surface of a phantom designed and built specifically for this project. Two diodes (old diode and new diode) were used in the investigation to observe the change in diode sensitivity after prolonged use. The results were also compared to those of other workers [8,10,15,20,23]. The results showed that the old and new diode both exhibited similar trends in all measurements though notable difference in their sensitivity can be observed. Large percentage deviations about ± 7 % were observed in the curved surface measurements. The diodes responded differently between the curved and flat surface measurements. The project showed that proper diode placement is necessary especially when performing measurements on curved surfaces.