Determining the focal spot limit of 1 MeV X-ray targets: Monte Carlo simulation of the point spread function

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• 作者：Jiayue Wang ; Jiaru Shi ; Wenhui Huang ; Chuanxiang Tang ; ^{tang.xuh@mail.tsinghua.edu.cn}
• 关键词：1  ; MeV X-ray ; Focal spot limit ; Point spread function (PSF) ; Monte Carlo simulation
• 刊名：Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
• 出版年：2017
• 出版时间：21 February 2017
• 年：2017
• 卷：846
• 期：Complete
• 页码：43-49
• 全文大小：952 K
• 卷排序：846

文摘

Among all microfocus X-ray tubes, 1 MeV has remained a “gray zone” despite its universal application in radiation therapy and non-destructive testing. One challenge existing in fabricating 1 MeV microfocus X-ray tubes is beam broadening inside metal anodes, which limits the minimum focal spot size a system can obtain. In particular, a complete understanding of the intrinsic broadening process, i.e., the point-spread function (PSF) of X-ray targets is needed. In this paper, relationships between PSF and beam energy, target thickness and electron incidence angle were investigated via Monte Carlo simulation. Focal spot limits for both transmission- and reflection-type tungsten targets at 0.5, 1 and 1.5 MeV were calculated, with target thicknesses ranging from 1μm to 2 cm. Transmission-type targets with thickness less than 5μm could achieve micrometer-scale spots while reflection-type targets exhibited superiority for spots larger than 100μm. In addition, by demonstrating the spot variation at off-normal incidence, the role of unidirectional beam was explored in microfocus X-ray systems. We expect that these results can enable alternative designs to improve the focal spot limit of X-ray tubes and benefit accurate photon source modeling.