DESIGN AND CONSTRUCTION OF RADON 222 CONCENTRATION METER USING SEMICONDUCTOR TRANSDUCER

Abstract

This thesis presents a method for monitoring radon concentration in air using a semiconductor photodiode as the transducer. A power supply unit, a simple ionization chamber, an analog system for signal discrimination and amplification, an embedded system based on arduino module microcontroller for measuring the transducer output and a Secured Digital (SD) Card Shield for logging measurement data were designed and constructed. The detection electrostatic chamber is made of a cylindrical aluminium tube with a copper rod running through the length of the tube and located at the tube axial centre. The body of the tube is the cathode while the copper wire is the anode. The Photodiode is fixed at the centre on the body of the tube and insulated from it. High Direct Current voltage of between 250 and 300V is applied to the chamber to ionize it. When radon decay, alpha particles are produced and accelerated to the cathode (the body of the chamber). The accelerated particles impinge on the semiconductor transducer fixed on the cathode and produces pulsation current whose peak is determined by the energy of the particle. The higher the number of energetic particles that are impinged on the transducer, the more the pulse current produced. The current pulse can then be counted and processed to give a measure of the concentration of the Radon. The developed system was tested and calibrated at Nigerian Institute of Radiation Protection (NIRP) Ibadan, Nigeria using Alpha 7401 Spectrometer available at the institute. The count per minute of the developed system has ±5% deviation with alpha 7401 spectrometer. The correlation value when the measurement of the two instruments was compared is 0.95. The total power consumption of the developed system is 1.5 watts.