A Novel Digital Read-Out System for Radiochromic Film Based on Synchronous Demodulation

This paper presents a novel apparatus designed to overcome the limitations of traditional radiochromic film read-out systems. Existing systems are often expensive and unsuitable for portable applications. The proposed system uses a narrowband LED to illuminate the radiochromic film under test, while a photodiode collects the scattered photons. The photogenerated current is converted into voltage and processed by a computational unit, which correlates the output signal with the absorbed dose level. To reduce noise and improve the signal-to-noise ratio, a synchronous demodulation technique is implemented digitally. The LED current is modulated by Pulse Width Modulation (PWM) and, using a sampling frequency four times the PWM frequency, the signal is demodulated in real-time with a numerically efficient algorithm. A microcontroller unit, running dedicated firmware, manages the entire circuitry and ensures suitability for IoT applications, as the system can transmit data to a remote server. The study details the system’s design and characterisation. Measurements conducted on EBT3 radiochromic films demonstrate its reproducibility, repeatability, and stability. The system is competitive as a dosimeter for nuclear medicine or environmental measurements, where low dose levels are common. The experimental study presented in this paper highlights this capability, demonstrating the apparatus as a cost-effective alternative to existing solutions on the market.