Metal organic frameworks: a novel material for the detection of radioactive gases Sharvanee Mauree, Vincent Villemot, Guillaume H.V. Bertrand, Matthieu Hamel, Benoît Sabot Université Paris Saclay, CEA, List, F-91120 Palaiseau, France The detection of radioactive gases is of utmost importance for radioprotection and is more challenging than solid sources of radioactivity due to their volatile nature. The gases targeted in this project are 85 Kr, 3 H and 222 Rn. The detection of 85 Kr is crucial for the radioprotection of the workers in nuclear power plants and is a sign of the core structural health of the power plant. 222Rn, is the second leading cause of lung cancer, following tobacco. 3 H detection is not only an indicator of nuclear military activity (hydrogen bombs) but also civil activities (fusion reactors, ITER). The techniques that exist for detecting these gases all present significant disadvantages, such as a bulky detection setup, and they cannot be used for online real-time detection [1,2] . This inadequate pool of detectors shows that there exists a real demand for a one-size-fits-all online detection system for radioactive gases. We propose using Metal Organic Frameworks (MOF) as a novel material for the adsorption and detection of those gases. MOFs are porous hybrid crystalline organic-inorganic materials, ideal for the adsorption of gases. Since the radioactive gases mentioned above are unstable radionuclides, they will disintegrate, emitting ionising radiation. Therefore, scintillation is another crucial property for this application. A scintillator is a material that produces photons in the presence of ionising radiation. The use of MOFs as scintillators was experimentally demonstrated in 2009 and, since has only been theorized for radioactive gas detection. By exposing the MOF to radioactive gas, we can detect the photons emitted by a MOF using a unique metrological gas bench detection system at the national metrological laboratory of France, shown in Figure 1 [3] . This system is compact and has demonstrated response times as fast as 1 min, which is ideal for online detection.
Figure 1: Illustrating the radioactive gas bench detection setup. We aim to synthesize pure millimetric single crystals of MOF since purity plays a vital role on the scintillating properties. With these innovative scintillating MOFs and the cutting-edge detection system, we have demonstrated that MOFs can indeed be used for detecting 85Kr. Statistical analysis also shows that this technique is reproducible over several cycles. Furthermore, not only were we able to detect 222 Rn, but we also demonstrated for the first time the measurement of its half-life using a MOF. We have also shown that a MOF can concentrate the radioactive gas within its pores, giving us access to a higher local concentration of radioactive species and hence a lower detection limit. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement no. 899293. References 1. Hou, X., Journal of Radioanalytical and Nuclear Chemistry, 318, pp. 1597–1628, 2018. 2. Takeyasu M., et al., SIERRA-II. J Radioanal Nucl Chem, 275, pp. 43–54, 2008. 3. Sabot B., et al., LSC 2020 International Conference on Advances in Liquid Scintillation Spectrometry, vol. 24, pp. 13–14, 2020.
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