Nuclear Techniques ›› 2015, Vol. 38 ›› Issue (12): 120503-120503.doi: 10.11889/j.0253-3219.2015.hjs.38.120503

• NUCLEAR PHYSICS, INTERDISCIPLINARY RESEARCH • Previous Articles     Next Articles

Air attenuation correction factor of free-air lionization chamber by means of vacuum measurement

LI Lun1,2 WU Jinjie2 GE Shuang2,3 CHEN Fajun1,2 WANG Peiwei2 YANG Yang2 LAI Wanchang1   

  1. 1(Chengdu University of Technology, Chengdu 610059, China) 2(National Institute of Metrology, Beijing 100029, China) 3(University of South China, Hengyang 421001, China)
  • Received:2015-06-09 Revised:2015-10-15 Online:2015-12-10 Published:2015-12-15
  • Contact: WU Jinjie, E-mail: wujj@nim.ac.cn E-mail:wujj@nim.ac.cn
  • About author:LI Lun, male, born in 1986, graduated from Chengdu University of Technology in 2010, master student, mainly engaged in X-ray measurement
  • Supported by:
    Supported by Quality Inspection of Public Welfare Industry Research Projects (No.201210003), Basic Scientific Research Business Class of the Chinese Academy of Metrology (No.25-AKY1307)

Abstract: Background: Air attenuation of free-air ionization chamber is one of the biggest correction terms and also has an influence on the total uncertainty of correction factor. Purpose: This study aims to measure the air attenuation correction factor for cylindrical free-air ionization chamber, and the correction of attenuation length between the diaphragm and the collecting region of cylindrical free-air ionization chamber in actual for the exact ionization current measurements. Methods: Molybdenum target X-ray vacuum tube test system and cylindrical free-air ionization chamber were used to measure the ionization current by means of vacuum. Electron Gamma Shower (EGSnrc) program was used to simulate constant pressure pipe for X-ray beam of the influence of additional losses. Results: The results showed that the ionization current of free-air ionization chamber was proportional to the pressure of the constant pressure pipe; and the extra loss of constant pressure pipe for X-ray beam was less than 0.5%; the design of the vacuum tube test system conformed to the requirements of experiment. Conclusion: For the air kerma absolute measurement of molybdenum target X-ray, the method of experimental measurement of air attenuation correction factor of cylindrical free air ionization chamber is of scientific reference value.

Key words: Vacuum method, Cylindrical free-air ionization chamber, EGSnrc program, Constant pressure pipe, Air attenuation, Correction factor