Calculation of Noble Gas Ion Mobility Based on SRK EOS Under High-Pressure

Abstract The time response characteristic of detectors in radiation imaging systems holds significant importance, and the response time of the detector will influence the image quality of the imaging system. However, the extended response time of parallel plate ionization chamber detectors currently in use contributes to image blurring. Enhancing the imaging quality necessitates a reduction in detector response time. There are many ways to reduce the response time of ionization chamber detectors. Modifying the working gas within the detector and opting for a working gas component with high ion mobility, while keeping the detector structure unchanged, has proven effective. Typically, gas detectors in radiation imaging systems contain noble gases at high pressure. To select the appropriate working gas components, we need to measure the mobility of ions of different gas components at high atmospheric pressure. Measuring the mobility of ions at high atmospheric pressure requires an accurate calculation of the molecular number density, and it is vital to choose an appropriate equation of state (EOS) for the gas. Hence, this paper suggests a method for calculating molecular number density grounded in the Soave-Redlich-Kwong (SRK) gas equation of state. It involves deriving the explicit form of the SRK equation and integrating an iterative approach to compute molecular number density in high-pressure gases. In order to compare the calculated results of different gas equations, various gas equations of state such as the Van Der Waals (VDW), Peng Robinson (PR) equation, ideal gas equation of state, etc. are utilized in this paper. The calculated results of the above equations are compared with the National Institute of Standards and Technology (NIST) data. The calculated results show that the SRK EOS is closer to the real value. The calculated results of the ideal gas equation of state deviate the most from the actual value. For some gases (e.g., krypton), the van der Waals equation has no real-number solution when the gas pressure is more than 2900KPa. Thus, in the subsequent measurements of the ion mobility of noble gases under high-pressure conditions, the ion mobility can be calculated with the assistance of the SRK equation and more accurate data can be obtained.