Periodic Reporting for period 3 - SPARTE (Scintillating Porous Architectures for RadioacTivE gas detection)
Reporting period: 2023-04-01 to 2024-12-31
Scintillating materials are widely used in detection systems addressing different fields: medical imaging, homeland security, high energy physics calorimetry, industrial control, and oil drilling exploration. These ionizing radiations are photons or particles such as gamma, X-ray, alpha, beta particles. While technology to detect gamma and X-rays is mature and commercially available, alpha and beta particles are trickier to detect due to their short mean free path in the matter including gas. In the case of beta it can range from a few tens of micrometres up to over centimetres in gas. They can thus hardly be detected from far as it is done for gamma rays. When their energy is reduced, their detection becomes critical because they must be almost in contact with the sensor. Beyond detecting the radioactive elements, metrology requires to quantify their activity, what involves modelling of the matter radiation. For most of the beta-active critical elements, there is no reliable and widely deployable technology.
In environmental laboratories liquid scintillation counting (LS) is the gold standard to measure radioactive liquids and H-3 in gas. In the case of gas analysis, it is bubbled in a solution containing an aromatic solvent and a fluorophore, what generates significant organic pollution, requires to mix gas and liquids, and takes about a week. On-site measurements for some isotopes use sophisticated technologies which cannot be widely deployed.
SPARTE aims to propose a breakthrough solution based on highly efficient porous scintillators enabling the detection and quantification of several critical radioactive rare gas isotopes of primary importance. The proposed materials are based on 3 different approaches: aerogels of inorganic nano-scintillator, aerogel of metal-organic-frameworks (MOF) showing an intrinsic porosity and crystal of MOF. The targeted isotopes are Kr-85, Xe-133, H-3, and potentially Ar-37.
Porous scintillators were produced and tested. The goal of online detection is achieved, with a detection efficiency of 17% for H-3 and nearly 100% for Kr-85 over an acquisition time of 100 seconds. Excellent linearity was observed, and an innovative approach enabling the measurement of gas mixtures is defined. A new measurement method for metrology purposes was developed, and a prototype of compact detector incorporating only 2 PMTs was produced and tested, allowing the detection of H-3 with 8% sensitivity.
In environmental laboratories liquid scintillation counting (LS) is the gold standard to measure radioactive liquids and H-3 in gas. In the case of gas analysis, it is bubbled in a solution containing an aromatic solvent and a fluorophore, what generates significant organic pollution, requires to mix gas and liquids, and takes about a week. On-site measurements for some isotopes use sophisticated technologies which cannot be widely deployed.
SPARTE aims to propose a breakthrough solution based on highly efficient porous scintillators enabling the detection and quantification of several critical radioactive rare gas isotopes of primary importance. The proposed materials are based on 3 different approaches: aerogels of inorganic nano-scintillator, aerogel of metal-organic-frameworks (MOF) showing an intrinsic porosity and crystal of MOF. The targeted isotopes are Kr-85, Xe-133, H-3, and potentially Ar-37.
Porous scintillators were produced and tested. The goal of online detection is achieved, with a detection efficiency of 17% for H-3 and nearly 100% for Kr-85 over an acquisition time of 100 seconds. Excellent linearity was observed, and an innovative approach enabling the measurement of gas mixtures is defined. A new measurement method for metrology purposes was developed, and a prototype of compact detector incorporating only 2 PMTs was produced and tested, allowing the detection of H-3 with 8% sensitivity.
We focused on the development and on the benchmarking of the scintillators, which were evaluated under various activities of Kr-85 as well as H-3. Material development was based on 3 alternative strategies:
1) aerogel type architectures based on inorganic scintillator nanoparticles. Their properties in the bulk state in terms of efficiency and timing allow to anticipate suitable performances. To date, we prepared Y3Al5O12 doped with cerium aerogels based on the previously developed nanoparticles, which are now functional and show excellent detection efficiency (about 95% for Kr and 17% for H-3). We reached detection sensitivity of 0.05 Bq/cm3 for tritium and Kr-85 measured in 100 s. With particular care of the radioactive background, we anticipate to improve the sensitivity by 1 order of magnitude at least. Several pieces of aerogel were produced thus confirming the reproducibility of the protocol. The tested aerogel made of LuF3:Ce, CeF3, YPO4:Ce and SiO2:Ce were not performing enough.
2) to elaborate MOF nanocrystals-based aerogels. To increase the intrinsic density, Hf based MOF were prepared. As building block, the scintillating properties were validated. In particular, it exhibits a very fast decay (<5 ns), suggesting the potential use of very short time windows. Its ability to adsorb noble gaz such as Ar, Xe and Kr was demonstrated, opening the route of concentration of radioactive elements. Monoliths were prepared from these Hf-MOF. The balance between porosity and transparency is still under study, but first monolith with improved transparency is obtained. Under radioactive gas exposure, the Hf-MOF building block shows a sensitivity down to 3 Bq/cm3 for Kr-85.
3) in using these MOF structures to produce single crystals in macroscopic format. Similarly, many formulations were explored and the most performing one demonstrates as polycrystalline assembly a detection limit at 6 Bq/cm3 and shows a good response linearity in the explored activity range.
In parallel:
• An innovative method using fine time analysis was tested to analyze gas mixtures. A mixture of H-3 and Kr-85 was measured, and their separate activities were evaluated online.
• Dedicated experimental set-up for porous analysis was validated (Compton TDCR experiment). It enables to establish the yield as a function of the electron energy and to deduce the potential detection efficiency for various gases. A dedicated set-up was also validated for radioactive gas measurement. Experiments with various activities were performed with Kr-85, H-3 and Rn-222 to extract linearity behaviours, detection limits and scintillation yields, which combined with gas exposure forms a new measurement method to detect low activity of pure beta emitters in gas.
• A prototype of low-cost detector involving only 2 PMTs and a simpler electronic was produced and successfully tested under Kr-85 and H-3 exposure. This prototype also enables the use of the method for measuring gas mixtures.
• 10 papers were published in peer-reviewed journals (Nature Photonics, Advanced materials, Advanced Functional materials) and 19 conference contributions were made.
1) aerogel type architectures based on inorganic scintillator nanoparticles. Their properties in the bulk state in terms of efficiency and timing allow to anticipate suitable performances. To date, we prepared Y3Al5O12 doped with cerium aerogels based on the previously developed nanoparticles, which are now functional and show excellent detection efficiency (about 95% for Kr and 17% for H-3). We reached detection sensitivity of 0.05 Bq/cm3 for tritium and Kr-85 measured in 100 s. With particular care of the radioactive background, we anticipate to improve the sensitivity by 1 order of magnitude at least. Several pieces of aerogel were produced thus confirming the reproducibility of the protocol. The tested aerogel made of LuF3:Ce, CeF3, YPO4:Ce and SiO2:Ce were not performing enough.
2) to elaborate MOF nanocrystals-based aerogels. To increase the intrinsic density, Hf based MOF were prepared. As building block, the scintillating properties were validated. In particular, it exhibits a very fast decay (<5 ns), suggesting the potential use of very short time windows. Its ability to adsorb noble gaz such as Ar, Xe and Kr was demonstrated, opening the route of concentration of radioactive elements. Monoliths were prepared from these Hf-MOF. The balance between porosity and transparency is still under study, but first monolith with improved transparency is obtained. Under radioactive gas exposure, the Hf-MOF building block shows a sensitivity down to 3 Bq/cm3 for Kr-85.
3) in using these MOF structures to produce single crystals in macroscopic format. Similarly, many formulations were explored and the most performing one demonstrates as polycrystalline assembly a detection limit at 6 Bq/cm3 and shows a good response linearity in the explored activity range.
In parallel:
• An innovative method using fine time analysis was tested to analyze gas mixtures. A mixture of H-3 and Kr-85 was measured, and their separate activities were evaluated online.
• Dedicated experimental set-up for porous analysis was validated (Compton TDCR experiment). It enables to establish the yield as a function of the electron energy and to deduce the potential detection efficiency for various gases. A dedicated set-up was also validated for radioactive gas measurement. Experiments with various activities were performed with Kr-85, H-3 and Rn-222 to extract linearity behaviours, detection limits and scintillation yields, which combined with gas exposure forms a new measurement method to detect low activity of pure beta emitters in gas.
• A prototype of low-cost detector involving only 2 PMTs and a simpler electronic was produced and successfully tested under Kr-85 and H-3 exposure. This prototype also enables the use of the method for measuring gas mixtures.
• 10 papers were published in peer-reviewed journals (Nature Photonics, Advanced materials, Advanced Functional materials) and 19 conference contributions were made.
These performances allow to develop a reference detection system, which does not exist so far, and thus a method of calibration for noble radioactive gases of low concentration-activity down to the level of mBq/cm3 at least. It is crucial for the Comprehensive Nuclear Test-Ban Treaty Organization since current reference methods are limited to about 300Bq/cm3 for only some isotopes such as Kr-85, Xe-133, H-3 and Xe-127. The SPARTE system surpasses this sensitivity. Since the concept and at least one material are secure and validated, we developed a reference measurement technique that aims to be implemented in other national metrology institutes. SPARTE had targeted 3 breakthrough objectives, and to date:
• while the current calibration methods are limited to 1kBq/m3 for Kr-85 and Xe-133, we have almost reached the first target: a detection sensitivity of mBq/cm3, which can be significantly improved using over pressure and increased measurement time.
• the second target was to achieve real time detection of H-3 with a significantly improved sensitivity in an easy deployable system. The current prototype is widely deployable for the H-3 as well as Kr-85.
• the third target was the detection of Ar-37. We could not obtain this radionuclide, but its low energy has been measured by the mean of synchrotron radiation and led to a sensitivity of 3%. We then consider the detection of 37Ar achievable. This isotope is strategic, as it is produced by the activation of calcium by high energy neutrons and has a relative long half-life time, what makes it a good indicator of underground nuclear tests.
These achievements allow to seriously consider the exploitation of detectors including H-3, Kr-85 for nuclear activity survey. The regulation requiring the Kr-85 and H-3 survey, the monitoring of radionuclides presents an important economic potential.
• while the current calibration methods are limited to 1kBq/m3 for Kr-85 and Xe-133, we have almost reached the first target: a detection sensitivity of mBq/cm3, which can be significantly improved using over pressure and increased measurement time.
• the second target was to achieve real time detection of H-3 with a significantly improved sensitivity in an easy deployable system. The current prototype is widely deployable for the H-3 as well as Kr-85.
• the third target was the detection of Ar-37. We could not obtain this radionuclide, but its low energy has been measured by the mean of synchrotron radiation and led to a sensitivity of 3%. We then consider the detection of 37Ar achievable. This isotope is strategic, as it is produced by the activation of calcium by high energy neutrons and has a relative long half-life time, what makes it a good indicator of underground nuclear tests.
These achievements allow to seriously consider the exploitation of detectors including H-3, Kr-85 for nuclear activity survey. The regulation requiring the Kr-85 and H-3 survey, the monitoring of radionuclides presents an important economic potential.