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: 2014
• 资助国家: 加拿大
• 起止时间: 2014-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=568000
• 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.

用高能质子束辐照在线同位素分离靶以产生稀有同位素束(RIB)是ISAC/TRIUMF的一种成熟的方法。亚原子物理研究中一些最具挑战性的项目需要具有极端数量的质子和中子的奇异元素，以深入了解物质的稳定性和元素的形成。为了向前沿研究提供非常短暂的肋骨，开发更好的靶点以适应它们的有效释放是必不可少的。即使最近有了重大改进，如复合陶瓷碳化铀靶材的开发，但越来越难以满足高调实验对肋骨的要求，例如非常富含中子的Ca和Be束。虽然对靶内产率可以做的相对较少，但通过将热力学和化学过程引导到所需的方向，可以显著减少同位素向离子源的流出时间，从而增加产量，特别是短寿命同位素的产量。然而，对于工作温度高达2300°C的ISOL靶中的这些过程的了解是有限的。质子束引起的核反应导致元素周期表上的每一种元素的产生都比目标材料本身轻。每种元素的渗出过程都是独一无二的，取决于其挥发性、温度、化学反应和化学计量比。一些最初的在线调查，例如，用CF4将氟化物的形成引导到所需的方向，是有希望的，但由于在线测试时间有限，并不是决定性的。我提出了一个研究项目，在现实操作条件下(温度、压力等)离线研究热力学和化学过程。在那里可以更精确地控制它们，并且许多样品的处理不受稀缺和昂贵的束流时间的限制。实验将在基于商用四极质谱计(QMS)的台式设备上进行，该仪器带有一个电离器单元和一个高温真空反应塔，作为在线靶标的简化模型。固体样品、挥发物和/或反应气体将通过快速进样进入色谱柱，以研究挥发和保留时间。这种设备的开发将结合我在原子束源和质谱学方面的专业知识，以及TRIUMF在高温炉和靶材制造方面的技术诀窍，例如钽的电子束焊接。这种高温炉质谱计(HTF-MS)为物理或/和化学专业的研究生提供了机会来研究各种有趣的问题，旨在研究折射物质从isol靶上的挥发。尤其是富含中子的Ca和Be同位素的挥发具有很高的优先级。它们最好是以足够的速率从鳗系氧化物或碳化物靶材中生产出来，缺点是Be或Ca以相对固定的氧化物或碳化物的形式保留在靶材中。挑战是研究钙和铍作为氟化物快速挥发的最佳条件。此外，还将对许多其他分子进行研究。