Hongguang Liu a, Haiwen Yu a, Ningbo Jia b, Jianquan Chen a, Mei Yang b, Zhengyi Sun a, Gang Yu c, Yudong Li c, Shouzhi Xi b, Fan Yang b, Tao Wang b, Wanqi Jie a
a School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, Shaanxi, 710072, China
b Imdetek Co., Ltd, Xi'an, Shaanxi, 712000, China
c Xinjiang Technical Institute of Physics and Chemistry, Urumqi, Xinjiang, 830011, China
## Abstract
The paper investigated the irradiation damage of CZT detectors caused by high flux an X-ray from X-ray tube operated at a tube voltage of 140 kV and an accumulated dose of 130 kGy. Deep-level transient spectroscopy (i-DLTS) was employed to characterize the defects. Four types of irradiation-induced defects were identified, corresponding to the energy levels at Ec-0.1eV, Ev+0.17eV, Ev+0.27eV and Ec-0.55eV, which are associated with the point defects, InCd+/0, VCd -/0, VCd 2−/− and TeCd 2+/+ respectively. After the irradiation, the concentration of VCd -/0 changed from 5.63 × 1012 cm−3 to 3.30 × 1013 cm−3 and VCd 2−/− increased from 1.13 × 1012 cm−3 to 1.88 × 1013 cm−3. The resistivity of all samples showed an upward trend after the irradiation, with the most significant change observed in sample 1, where it doubled from 1.09 × 1011 Ω cm to 1.94 × 1011 Ω cm. However, the energy resolution for the spectrum peak of 241Am (59.5 keV) decreased from 6.2% to 10.7% and the signal noise to ratio decreased from 42.24 to 27.33 when irradiated from anode. The counting performance of the photon counting module decreased by approximately 1.81% after irradiation on the cathode side.
## Introduction
Cadmium Zinc Telluride (CdZnTe or CZT) has been widely used in various fields, including security inspection, space science, nuclear science, astronomical observations, medical imaging and more [[1], [2], [3]].
In 2021, the first FDA-approved photon-counting CT, named NAEOTOM Alpha, made its debut from Siemens Healthineers [4,5]. With the development of detectors and the gradual maturation of CZT detector applications, the irradiation effects on the stability of these detectors have become an important issue that requires thorough understanding.
Currently, research on irradiation damage of CZT crystals mainly focused on high-energy γ-Ray, heavy ions, neutrons and so on. Liang [6] investigated the irradiation damage of CZT detectors caused by heavy ion irradiation with an energy of 20 MeV and found that chlorine ion irradiation primarily introduced deep-level defects. After irradiation, the electron mobility significantly decreased from 658 cm2V−1s−1 to 267 cm2V−1s−1, and the energy resolution of γ-Ray spectrum reduced from 8% to 26.8%. Cavallini [7] investigated γ-ray irradiation on CZT detectors and the results indicated that 60Co spectrum properties deteriorated terribly after increasing the radiation dose of γ-rays up to 30 kGy.
In real working conditions of the photon-counting CT, detectors are exposed to X-rays for extended periods, which may differ from the irradiation damage caused by high-energy γ-Ray and heavy ions. Fraboni [8] studied the X-ray irradiation damage of CZT crystals under a tube voltage of 35 kV with a total dose of 260 kGy. At this dose, significant changes in defect concentrations at energy levels of 0.06 eV, 0.41 eV, and 0.53 eV were observed, leading to a substantial decrease in detection performance. However, the photon energy is typically less than 200 keV in medical instruments. There have been no investigations on CZT detectors about X-ray irradiation damage at this condition yet.
This study focused on irradiation damage of CZT detectors caused by X-ray with energy less than 140 keV, aimed at the application of photon-counting CT.
CdZnTe Association (CdZnTe.com)
https://www.cdznte.com/thesis/the-effect-of-low-energy-high-dose-x-ray-irradiation-on-the-performance-of-cdznte-detector.html