Design of Activated Charcoal Trap Based on Semiconductor Refrigeration

Xenon (Xe) concentration and isotope ratios measurements are crucial in the nuclear industry, nuclear safeguards supervision, frontier science and other fields. However, due to its minimal presence in atmospheric composition, especially in atmospheric particulate matter and atmospheric radioactive xenon samples, efficient separation of minuscule xenon presents a significant challenge. One of the most commonly used methods is to separate xenon gases by using the principle of adsorption temperature difference between noble gases on activated charcoal. Activated charcoal can selectively adsorb Xe at low temperatures, making it an efficient adsorbent. Thermoelectric refrigeration technology based on semiconductors has the advantages of low noise, run steadily, low material consumption, and long service life, and is widely used in spaceflight, medical care, and biopharmaceutical industries. A compact activated charcoal trap based on technology of semiconductor refrigeration was designed. The activated charcoal trap device is mainly composed of four parts: adsorption module, heat conduction module, refrigeration module and heat dissipation module. In order to improve the cooling effect of activated charcoal particles, the elasticity of copper mesh was used to support activated charcoal particles on the stainless steel pipe wall. Xe in the mixed gas was adsorbed by reducing the temperature of the trap, subsequently released by heating to 180 ℃. After purification, the concentration and isotope ratio of Xe were measured by Helix MC Plus static gas mass spectrometer. Experimental results demonstrate that the lowest achieved temperature of activated charcoal trap is −37 ℃ with a refrigeration time of just 180 seconds. The recovery of Xe reaches 81% and the separation coefficient of Kr from Xe is above 188. For a sample injection of approximately 1×10−13 mol, the relative standard deviation (RSD) of Xe isotope ratio analysis is 0.06%-0.12% by Faraday tube, and the relative deviation between the measured value and certified value is −0.14%-0.22%, excluding 124Xe/132Xe, 126Xe/132Xe, and 128Xe/132Xe. Among them, the relative deviation between the measured value and the reference value of 129Xe/132Xe, 130Xe/132Xe and 134Xe/132Xe is −0.03%-0.07%. The measured results are stable and accurate, the reproducibility of the test process is good, and no obvious isotopic fractionation is observed during sample processing and measurement. The compact activated charcoal trap designed in this paper can be cooled swiftly and stably, with a processing time of sample preparation about 0.5 hours. Combined with static gas mass spectrometry, it enables high precision analysis of Xe isotope ratios, offering technical support for the monitoring of atmospheric particulate matter and atmospheric radioactive xenon gases in nuclear safeguards and nuclear environmental monitoring.