Khalil Mohamad, Dreier Erik Schou, Kehres Jan, Jakubek Jan, Olsen Ulrik Lund
Department of Physics, NEXMAP Section, Technical University of Denmark, Fysikvej, Lyngby, Copenhagen 2800, Denmark.
Department of Physics, University of Copenhagen, Nørregade 10, Copenhagen 1165, Denmark.
J Synchrotron Radiat. 2018 Nov 1;25(Pt 6):1650-1657. doi: 10.1107/S1600577518013838. Epub 2018 Oct 26.
Timepix3 (256 × 256 pixels with a pitch of 55 µm) is a hybrid-pixel-detector readout chip that implements a data-driven architecture and is capable of simultaneous time-of-arrival (ToA) and energy (ToT: time-over-threshold) measurements. The ToA information allows the unambiguous identification of pixel clusters belonging to the same X-ray interaction, which allows for full one-by-one detection of photons. The weighted mean of the pixel clusters can be used to measure the subpixel position of an X-ray interaction. An experiment was performed at the European Synchrotron Radiation Facility in Grenoble, France, using a 5 µm × 5 µm pencil beam to scan a CdTe-ADVAPIX-Timepix3 pixel (55 µm × 55 µm) at 8 × 8 matrix positions with a step size of 5 µm. The head-on scan was carried out at four monochromatic energies: 24, 35, 70 and 120 keV. The subpixel position of every single photon in the beam was constructed using the weighted average of the charge spread of single interactions. Then the subpixel position of the total beam was found by calculating the mean position of all photons. This was carried out for all points in the 8 × 8 matrix of beam positions within a single pixel. The optimum conditions for the subpixel measurements are presented with regards to the cluster sizes and beam subpixel position, and the improvement of this technique is evaluated (using the charge sharing of each individual photon to achieve subpixel resolution) versus alternative techniques which compare the intensity ratio between pixels. The best result is achieved at 120 keV, where a beam step of 4.4 µm ± 0.86 µm was measured.
Timepix3（256×256像素，像素间距为55微米）是一种混合像素探测器读出芯片，采用数据驱动架构，能够同时进行到达时间（ToA）和能量（ToT：阈值时间）测量。ToA信息可明确识别属于同一X射线相互作用的像素簇，从而实现光子的逐个完全检测。像素簇的加权平均值可用于测量X射线相互作用的亚像素位置。在法国格勒诺布尔的欧洲同步辐射装置上进行了一项实验，使用5微米×5微米的铅笔束，以5微米的步长在8×8矩阵位置扫描一个CdTe - ADVAPIX - Timepix3像素（55微米×55微米）。在四种单色能量下进行了正面扫描：24、35、70和120千电子伏特。利用单次相互作用电荷分布的加权平均值构建束中每个光子的亚像素位置。然后通过计算所有光子的平均位置来确定整个束的亚像素位置。对单个像素内束位置的8×8矩阵中的所有点都进行了此操作。针对簇大小和束亚像素位置给出了亚像素测量的最佳条件，并评估了该技术的改进情况（利用每个光子的电荷共享实现亚像素分辨率），与比较像素间强度比的替代技术进行了对比。在120千电子伏特时取得了最佳结果，测得束步长为4.4微米±0.86微米。
