Radiation dose measurements in irradiated PMMA using ultrasonic technique

Polymethylmethacrylate (PMMA) samples of 20 mm thickness and 50 mm diameter were prepared by machining from a half a metre rod and exposed to γγ-ray dose for different durations in an irradiation chamber with Co-60 source. Prominent radiation induced colouration as function of absorbed dose was observed in the irradiated samples. Precise ultrasonic velocity measurements were made in the irradiated samples using 2 MHz longitudinal ultrasonic wave contact type transducer. Measurements indicate that up to 89 kGy of absorbed dose there is no pronounced change in the ultrasonic velocities. Further exposure of samples up to 267 kGy decreases the ultrasonic velocity continuously. From the experimental data points, a graph was drawn with measured velocity as function of absorbed dose. A quantitative linear correlation was obtained between ultrasonic velocity and the absorbed dose for the γγ-ray dose range 50–250 kGy. Present study suggests that a reliable radiation dosimeter can be developed employing precise ultrasonic velocity measurements in commercially available PMMA as the medium for propagation of ultrasonic waves.