Images of resolved 5.9 keV electron tracks produced from $^{55}$Fe X-ray interactions are presented for the first time using an optical readout time projection chamber (TPC). The corresponding energy spectra are also shown, with the FWHM energy resolution in the 30-40\% range depending on gas pressure and gain. These tracks were produced in low pressure carbon tetrafluoride (CF$_4$) gas, and imaged with a fast lens and low noise CCD camera system using the secondary scintillation produced in GEM/THGEM amplification devices. The GEM/THGEMs provided effective gas gains of $\gtrsim 2 \times 10^5$ in CF$_4$ at low pressures in the 25-100 Torr range. The ability to resolve such low energy particle tracks has important applications in dark matter and other rare event searches, as well as in X-ray polarimetry. A practical application of the optical signal from $^{55}$Fe is that it provides a tool for mapping the detector gain spatial uniformity.

中文翻译：

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使用 CCD 读出器对基于 GEM 的 TPC 中的 55Fe 电子轨迹进行成像

使用光学读出时间投影室 (TPC) 首次呈现了由 $^{55}$Fe X 射线相互作用产生的已解析 5.9 keV 电子轨迹的图像。还显示了相应的能谱，FWHM 能量分辨率在 30-40% 范围内，具体取决于气压和增益。这些轨迹是在低压四氟化碳 (CF$_4$) 气体中产生的，并使用快速镜头和低噪声 CCD 相机系统使用 GEM/THGEM 放大设备中产生的二次闪烁成像。GEM/THGEM 在 25-100 Torr 范围的低压下以 CF$_4$ 提供了 $\gtrsim 2 \times 10^5$ 的有效气体收益。解析这种低能量粒子轨迹的能力在暗物质和其他稀有事件搜索以及 X 射线偏振测量中具有重要应用。