Thermal separation of volatile rare isotopes from irradiated target materials

放射免疫治疗、靶向α粒子治疗和相关成像技术等非常有前途的放射治疗方法的研究，受到极其罕见和相对短暂的同位素（如209,2111at、225,226Ac、223,224Ra、213Bi或212Pb）的有限可用性的阻碍。一种合适的生产方法，特别是对于那些不能通过核反应堆或低能医用回旋加速器等传统来源轻易获得的同位素，由同位素分离在线（ISOL）设施如TRIUMF/ISAC（同位素分离和加速）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同位素束，但最近为核医学研究提供209,211At和225,226Ac样品的努力取得了优异的成果。ISOL方法的优点是，通过注入质量分离离子束，可以产生同位素和化学纯度高的样品。随后，耗时的化学分离和净化步骤要么相对简单，要么没有必要。该方法的缺点是可以从ISOL目标中提取的数量受到目标大小，低提取效率和波束时间可用性的限制。因此，依靠ISOL源同位素的核医学实验基本上仅限于基础的临床前研究。同位素生产目标与后续化学分离目标之间的主要区别在于它们的工作温度。前者是主动冷却的，可以实现高光束强度的辐射，将整个同位素生产库存保留在目标内。相比之下，ISOL靶标在高达2300°C的高温下操作，以促进在靶标照射时快速有效地释放足够挥发性的化学物质。该提案旨在研究两种方法的结合，其中由耐火材料制成的生产目标被转移到高温真空炉中，从那里通过扩散和渗出从辐照的目标材料中提取挥发性物质的馏分。这需要对驱动挥发性物质从目标中释放和热色谱分离的热力学和化学进行调查、理解和随后的优化。这包括开发、测试和优化合适的实验装置。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易挥发但寿命较短的治疗系统209,211At及其前体211Rn。第二个主要目标是研究在更高温度下从碳化锕靶中释放的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进行研究。

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.