Nuclear Techniques ›› 2018, Vol. 41 ›› Issue (7): 70201-070201.

• LOW ENERGY ACCELERATOR, RAY AND APPLICATIONS •

### Evaluation for low energy γ proportion of cobalt source high dose rate field based on plane-parallel ionization chamber

LI Lei, SHI Jianmin, YANG Na, PANG Yuanlong, LIU Xuqiang, ZENG Guang, YANG Guixia

1. Institute of Nuclear Physics and Chemistry, Chinese Academy of Engineering Physics, Mianyang 621900, China
• Received:2016-12-20 Revised:2017-07-09 Online:2018-07-10 Published:2018-07-07

Abstract: [Background] Heavy metal process is widely used to improve the reliability of electronic devices, which introduces interface formed by high Z and low Z material. There will be dose enhancement effect within region near such interface when exposing to low energy γ-ray field. This phenomenon could affect the reliability of hardness assurance tests. [Purpose] A method was introduced to evaluate the proportion of low energy scattering γ-ray within high dose rate irradiation field formed by cobalt source. [Methods] Two types of ionization chambers were designed, which utilize single layer Al(aluminum) wall and double layers Au(gold)/Al wall respectively. The γ-ray induced current of the latter ionization chamber varied more rapidly with the change of γ-ray energy than the former one. Consequently, the ratio of those two currents was sensitive to γ-ray energy, and the variation between measured and reference value of ratio could indicate whether the proportion of low energy γ-ray was over expectation obviously. [Results] It was advised that the reference value could be set as 2.8 based on analysis of typical energy spectrums of cobalt source. In addition, an ionization chamber dosimeter system with the range of 0.01~2.3Gy·s-1(Si) was designed with which the ratios were measured in free field and Pb(lead)/Al box reducing the amount of low energy γ-ray. There was an agreement between experimental and calculated results. [Conclusion] The method is effective for evaluating the proportion of scattering γ-ray and the effectiveness of spectral hardening technology. Furthermore, it could help correlate different irradiation fields or irradiation positions within specific irradiation field from the aspect of irradiation dose.

CLC Number:

• TL929