Thermal separation of volatile rare isotopes from irradiated target materials

在放射免疫治疗、靶向阿尔法粒子治疗和相关成像技术等放射治疗方法方面非常有前途的研究，由于极其稀有和相对短暂的同位素，如209,211At，225,226Ac，223,224Ra，213Bi或212Pb的有限可获得性而受到阻碍。一种合适的生产方法，特别是通过核反应堆或低能量医用回旋加速器等传统来源无法轻易获得的同位素，由TRIUMF/ISAC(同位素分离和加速)等ISOL(在线同位素分离)设施提供。尽管ISAC的主要目的是为核物理和材料科学领域的研究提供稀有的同位素束，但最近为核医学研究提供209,211 At和225,226 Ac样品的努力取得了良好的结果。ISOL方法的优点是，通过注入分离质量的离子束，可以得到同位素和化学纯度较高的样品。随后耗时的化学分离和提纯步骤要么相对简单，要么不必要。该方法的缺点是可以从ISOL目标提取的量受到目标大小、低提取效率和波束时间可用性的限制。因此，依赖于来自isol来源的同位素的核医学实验基本上局限于基础的临床前研究。随后进行化学分离的同位素生产目标与ISOL目标之间的主要区别在于它们的工作温度。前者被主动冷却，能够进行高束强度的辐射，将整个同位素生产库存保留在靶子内。相比之下，ISOL靶在高达2300摄氏度的非常高的温度下运行，以促进在辐照靶时快速有效地释放充分挥发的化学物质。这一建议旨在研究两种方法的组合，即将耐火材料制成的生产目标转移到高温真空炉中，从受照射的目标材料中通过扩散和渗流提取部分挥发性物质。它需要调查、了解和随后优化推动挥发性物质从目标释放和热色谱分离的热力学和化学。这包括开发、测试和优化合适的实验设置。该提案的两个主要目标之一是找到一种快速有效的方法来提取相对挥发性但寿命较短的硫化体系209,211At及其前体211Rn。第二个主要目标是研究在更高的温度下从光化碳化物靶中释放的Ra和Ac同位素的热分离。从长远来看，任何对收获感兴趣的同位素都可以被研究。

Very promising research on radio-therapeutic methods like radio-immunotherapy, targeted alpha-particle therapy and associated imaging techniques is hampered by the limited availability of extremely rare and relatively short-lived isotopes like 209,211At, 225,226Ac, 223,224Ra , 213Bi or 212Pb. A suitable production method, in particular for isotopes that can't be easily obtained via traditional sources like nuclear reactors or low-energy medical cyclotrons, is provided by ISOL (Isotope Separation OnLine) facilities like TRIUMF/ISAC (Isotope Separation and ACceleration). Even though the main purpose of ISAC is to supply rare isotope beams for research in the fields of nuclear physics and material science, recent efforts to provide samples of 209,211At and 225,226Ac for nuclear medicine research have yielded excellent results. The advantage of the ISOL method is that via the implantation of mass-separated ion beams isotopically and chemically pure samples can be produced. Subsequent, time consuming chemical separation and purification steps are either relatively straightforward or unnecessary. The disadvantage of the method is that the quantities that can be extracted from an ISOL target are limited by target size, low extraction efficiencies and beamtime availability. Therefore, nuclear medicine experiments relying on isotopes from an ISOL source are essentially restricted to basic pre-clinical studies. A major difference between a production target for isotopes with subsequent chemical separation and an ISOL target is their operating temperature. The former is actively cooled, enabling iradiations with high beam intensities, retaining the entire isotope production inventory inside the target. In contrast, ISOL targets are operated at very high temperatures up to 2300 °C to facilitate the fast and efficient release of sufficiently volatile chemical species while the target is irradiated. This proposal aims at research into a combination of both methods, in which a production target made from refractory materials is transferred to a high-temperature vacuum furnace from where fractions of volatile species are extracted from the irradiated target material by diffusion and effusion. It requires the investigation, understanding and subsequent optimization of the thermodynamics and chemistry driving the release and thermo-chromatographic separation of volatile species from a target. This includes development, testing and optimization of suitable experimental setups. One of the two main objectives of the proposal is to find a fast and efficient method for the extraction of the relatively volatile but also short-lived theranostic system 209,211At and its precursor 211Rn. The second main objective is the investigation of thermal separation of Ra and Ac isotopes which are released from actinde carbide targets at much higher temperatures. In the long run, any isotope of interest for harvesting could be investigated.