Simulation study of energy resolution with changing pixel size for radon monitor based on Topmetal-\({II}^-\) TPC

  • Meng-Yao HuangEmail author
  • Hua Pei
  • Xiang-Ming Sun
  • Shu-Guang Zou


In this paper, we study how pixel size influences energy resolution for a proposed pixelated detector—a high sensitivity, low cost, and real-time radon monitor based on a Topmetal-\({II}^-\) time projection chamber (TPC). This monitor was designed to improve spatial resolution for detecting radon alpha particles using Topmetal-\({II}^-\) sensors assembled by a 0.35 μm CMOS integrated circuit process. Owing to concerns that small pixel size might have the side effect of worsening energy resolution due to lower signal-to-noise ratio, a Geant4-based simulation was used to investigate the dependence of energy resolution on pixel sizes ranging from 60 to 600 μm. A non-monotonic trend in this region shows the combined effect of pixel size and threshold on pixels, analyzed by introducing an empirical expression. Pixel noise contributes 50 keV full-width at half-maximum energy resolution for 400 μm pixel size at 1–4\(\sigma\) threshold that is comparable to the energy resolution caused by energy fluctuations in the TPC ionization process (\(\sim \,20\) keV). The total energy resolution after combining both factors is estimated to be 54 keV for a pixel size of 400 μm at 1–4\(\sigma\) threshold. The analysis presented in this paper would help choosing suitable pixel size for future pixelated detectors.


Geant4 Energy resolution Pixel size Radon monitor Topmetal 


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Copyright information

© China Science Publishing & Media Ltd. (Science Press), Shanghai Institute of Applied Physics, the Chinese Academy of Sciences, Chinese Nuclear Society and Springer Nature Singapore Pte Ltd. 2019

Authors and Affiliations

  • Meng-Yao Huang
    • 1
    Email author
  • Hua Pei
    • 2
  • Xiang-Ming Sun
    • 2
  • Shu-Guang Zou
    • 3
  1. 1.Department of Physics and AstronomyIowa State UniversityAmesUSA
  2. 2.PLAC, Key Laboratory of Quark & Lepton Physics (MOE)Central China Normal UniversityWuhanChina
  3. 3.College of Information Science and EngineeringHenan University of TechnologyZhengzhouChina

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