Influence of CCD Camera Transient Noise on Imaging Resolution and Shielding Requirement in Neutron Radiography

The CCD camera is widely used as imaging equipment in neutron radiography system. In the exposures of neutron radiography, transient noises are produced from CCD camera due to the neutron and gamma radiations, and reduce the image resolution. It is necessary to study systematically the shielding design requirements of CCD camera. In this paper, the functional relationship of transient noise to image resolution and transient noise to radiation dose for a typical CCD camera were obtained respectively by the theoretical derivation of the modulation transfer function (MTF) and CCD camera radiation experiments with different isotope sources. Based on the two functional relationships, the upper limit of radiation dose of CCD camera was obtained. The results show that for the 10 lp/mm imaging resolution, the proportion of transient noise needs to be controlled with ≤8%. Therefore, the upper limits of single imaging irradiation doses of Am-Be neutron radiation, ¹³⁷Cs and ⁶⁰Co γ radiations are 3.22×10^-5, 2.64×10^-3 and 4.44×10^-3 Gy respectively. The reason that the neutron dose limit below the gamma dose limit, and the highenergy gamma dose limit below the lowenergy gamma dose limit is explained.