We designed and optimized a novel device "target" that directs a CO2 gas pulse onto a Ti surface where a Cs+ beam generates C- from the CO2. This secondary ionization target enables an accelerator mass spectrometer to ionize pulses of CO2 in the negative mode to measure 14C/12C isotopic ratios in real time. The design of the targets were based on computational flow dynamics, ionization mechanism and empirical optimization. As part of the ionization mechanism, the adsorption of CO2 on the Ti surface was fitted with the Jovanovic-Freundlich isotherm model using empirical and simulation data. The inferred adsorption constants were in good agreement with other works. The empirical optimization showed that amount of injected carbon and the flow speed of the helium carrier gas improve the ionization efficiency and the amount of 12C- produced until reaching a saturation point. Linear dynamic range between 150 and 1000 ng of C and optimum carrier gas flow speed of around 0.1 mL/min were shown. It was also shown that the ionization depends on the area of the Ti surface and Cs+ beam cross-section. A range of ionization efficiency of 1-2.5% was obtained by optimizing the described parameters.

中文翻译：

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设计二次电离靶，用于直接从 CO2 脉冲产生 C 束，用于在线 AMS。


我们设计并优化了一种新颖的装置“靶”，它将 CO2 气体脉冲引导到 Ti 表面，其中 Cs+ 束从 CO2 中产生 C-。这种二次电离靶使加速器质谱仪能够以负模式电离 CO2 脉冲，从而实时测量 14C/12C 同位素比。目标的设计基于计算流动动力学、电离机制和经验优化。作为电离机制的一部分，CO2 在 Ti 表面上的吸附使用经验和模拟数据与 Jovanovic-Freundlich 等温线模型进行拟合。推断的吸附常数与其他工作非常一致。经验优化表明，注入碳的量和氦载气的流速提高了电离效率和 12C- 的产生量，直至达到饱和点。显示了 150 至 1000 ng C 之间的线性动态范围和约 0.1 mL/min 的最佳载气流速。研究还表明，电离取决于 Ti 表面的面积和 Cs+ 束横截面。通过优化所述参数获得了 1-2.5% 的电离效率范围。