Offline investigation of thermodynamic and chemical processes in targets for radioactive beam production

放射性束产生目标的热力学和化学过程的离线研究

• 批准号: SAPIN-2014-00021
• 负责人: Kunz, Peter
• 金额: $ 1.97万
• 依托单位: Simon Fraser University
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=617815
• 关键词: Offline; investigation; thermodynamic; chemical; processes

The irradiation of ISOL (isotope separation on-line) targets with high-energy proton beams for the production of rare isotope beams (RIB) is a well-established method at ISAC/TRIUMF. Some of the most challenging projects in subatomic physics research are in need of exotic elements with extreme numbers of protons and neutrons to gain insight in the stability of matter and the formation of the elements. In order to provide cutting-edge research with very short-lived RIB, the development of better targets to accommodate their efficient release is essential.Even with recent major improvements, such as the development of composite ceramic uranium carbide targets, it becomes increasingly difficult to accommodate requests of high-profile experiments for RIB, e.g. very neutron-rich Ca and Be beams. While relatively little can be done about in-target production rates, the effusion times of isotopes to the ion source could be decreased significantly by steering thermodynamic and chemical processes into the desired direction, thus, increasing the yields especially of short-lived isotopes. However, the understanding of these processes in ISOL targets with operating temperatures as high as 2300° C, is limited.The nuclear reactions induced by the proton beam lead to the production of every element on the periodic table lighter than the target material itself. The effusion process is unique for every element and depends on its volatility, temperature, chemical reactions and stoichiometric ratios. Some initial on-line investigations, for example, steering the formation of fluorides into the desired direction with CF4, were promising, but not conclusive due to the limited availability of online testing time.I propose a research project to investigate thermodynamic and chemical processes offline under realistic operating conditions (temperature, pressure, etc.) where they can be controlled much more accurately and where the processing of many samples is not limited by scarce and expensive beam time. The experiments will be performed with a table-top apparatus based on a commercial quadrupole mass spectrometer (QMS) with an ionizer unit and a high-temperature vacuum reaction column which serves as a simplified model for an online target. Solid samples, volatiles and/or reaction gases will be introduced into the column via a fast injection for the investigation of volatilization and retention times. The development of such an apparatus will combine my expertise with atomic beam sources and mass spectrometry and the know-how at TRIUMF on high-temperature furnaces and target fabrication, e. g. e-beam welding of tantalum.Such a high-temperature furnace mass spectrometer (HTF-MS) offers the opportunity for graduate students with a physics or/and chemistry major to work on a variety of interesting questions, aiming at the volatilization of refractive species from an ISOL target. In particular the volatilization of the neutron-rich Ca and Be isotopes has a high priority. They are best produced with sufficient rates from actinide oxide or carbide targets with the disadvantage that Be or Ca are retained within the target matrix as relatively immobile oxides or carbides. The challenge is to investigate the optimal conditions for the fast volatilization of Ca and Be as fluorides. Additionally, a multitude of other molecules will be investigated as well.

用高能质子束照射 ISOL（在线同位素分离）靶来产生稀有同位素束 (RIB) 是 ISAC/TRIUMF 的一种成熟方法，亚原子物理研究中一些最具挑战性的项目是。需要具有极端数量的质子和中子的奇异元素来深入了解物质的稳定性和元素的形成，以便为非常短命的 RIB 提供尖端研究，开发更好的靶材来适应它们的释放至关重要。即使最近有了重大改进，例如复合陶瓷碳化铀靶材的开发，满足高调高效 RIB 实验的要求（例如富中子实验）变得越来越困难。虽然 Ca 和 Be 束在达到目标生产率方面可以做的事情相对较少，但通过将热力学和化学过程转向所需的方向，可以显着减少同位素到离子源的流出时间，从而提高产量，尤其是然而，对工作温度高达 2300°C 的 ISOL 靶中的这些过程的理解是有限的。质子束引起的核反应导致产生周期表上比元素轻的所有元素。每种元素的渗流过程都是独特的，并且取决于其挥发性、温度、化学反应和化学计量比，例如，将氟化物的形成引导到所需的方向。 CF4，很有希望，但由于在线测试时间有限，还没有结论。我提出了一个研究项目，在现实操作条件（温度、压力等）下离线研究热力学和化学过程，在这些条件下可以更准确地控制它们并且许多样品的处理不受稀缺和昂贵的束流时间的限制，实验将使用基于带有电离器单元和高温真空反应柱的商用四极杆质谱仪（QMS）的台式设备进行。哪个服务作为在线目标的简化模型，固体样品、挥发物和/或反应气体将通过快速注射引入色谱柱，以研究挥发和保留时间。这种设备的开发将我的专业知识与原子束结合起来。来源和质谱以及 TRIUMF 在高温炉和靶材制造方面的专业知识，例如高温炉质谱仪。 (HTF-MS) 为物理或/和化学专业的研究生提供了研究各种有趣问题的机会，旨在研究 ISOL 目标中折射物质的挥发，特别是富中子 Ca 的挥发。 Be 同位素具有较高的优先级，它们最好以足够的速率从锕系氧化物或碳化物靶中生产，缺点是 Be 或 Ca 作为相对固定的氧化物或碳化物保留在靶基体中。研究 Ca 和 Be 作为氟化物快速挥发的最佳条件。此外，还将研究许多其他分子。