Implementation of DAP rate Meter Prototype for Transparent Ionization Chamber

• Main Authors: Chang, Chan., 張 展
• Other Authors: Jong, Tai-Lang
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/h5vbap

碩士 === 國立清華大學 === 電機工程學系所 === 106 === The objective of this thesis is to develop a dose area product (DAP) rate meter prototype for transparent ionization chamber to monitor the radiation dose. When X-ray irradiates the ionization chamber, the radiation causes air to ionize, producing electrons which are collected by the charge collection electrode to form the electron flow, the current signal is then converted into a voltage signal through the transimpedance amplifier (TIA). The MSP430F5438 Experimenter Board converts the analog voltage signal into digital form via ADC and then calculates the electron flow, which then mutiplies the pertinent calibration factors to obtain the DAP rate. This thesis uses Altium Designer14 to design a PC board for transimpedance amplifiers, SolidWorks2017 to design the instrument case, and Texas Instruments Code Composer Studio V6 as a program development environment to design programs for controlling the MSP430F5438 experimenter board’s UART and I/O ports, LCD, switches and four major instrument functions, such as parameter setting, current and temperature measurement, data transmission, and button test. The meter can use the switch to select different measurement ranges. When the measurement range is 0.3 nA~40 nA, the measurement error is about 1%; the measurement range is 10pA~700 pA, and the error can be less than 1%. The electron flow collected by the spherical ionization chamber when X-ray is used as the radiation source is measured by our prototype for various X-ray tube voltages: 80kV, 120kV, 150kV, tube currents: 5mA, 10mA, 15mA, 20mA, 25mA, 30mA, and with the high-voltage module of our prototype provides the negative high voltage to the spherical ionization chamber’s electrode plate. Measurements of same X-ray tube voltage and current conditions are also performed by using INER’s measurement instrument (Keithly6517A) and high voltage power supply (Keithly247). The errors between measurement results of our prototype and INER’s instruments are mostly less than 1.5%. The prototype meter is indeed suitable for measuring the weak current of the ionization chamber in real time.