Precision measurements with trapped radioactive ions using the Canadian Penning Trap Mass spectrometer and associated ion traps at the Argonne National Laboratory

使用阿贡国家实验室的加拿大彭宁阱质谱仪和相关离子阱对捕获的放射性离子进行精确测量

• 批准号: SAPPJ-2014-00024
• 负责人: Sharma, Kumar
• 金额: $ 8.01万
• 依托单位: University of Manitoba
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Project
• 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=568020
• 关键词: Precision; measurements; trapped; radioactive; ions

This work centres on the precise measurement of the atomic masses and other properties of nuclei far from stability. The results provide information on the energy released in nuclear reactions involving nuclei in these exotic regions. Such information is important in predicting the rates and pathways of nuclear reactions that power explosive astrophysical events that are candidates for the nucleosynthesis of the heavier elements (through the rp-, nu-p- and r-processes). They also allow the study of fundamental symmetries in particle physics theories and the evolution of nuclear structure in regions where the nuclei have extreme neutron-to-proton ratios. The measurements are conducted with the Canadian Penning Trap Mass Spectrometer (CPT) which operates on-line to the ATLAS accelerator system at the Argonne National Laboratory. The energetic products of nuclear reactions are slowed in a gas cell and collected, cooled and purified in a series of ion traps. This ion-cloud of exotic nuclides is then transferred to a precision Penning trap where the mass of the ions can be measured to precisions of a few parts per billion. Alternately, the ions can also be transferred to a radio-frequency quadrupole ion trap (RFQ) where they are suspended in helium gas. Such a cloud of exotic nuclei, nearly at rest, provides a unique opportunity to study the correlations between the beta particles and the neutrinos and other particles emitted in their decay. The following initiatives are either planned or in progress: • The CPT has been moved from its original location and installed on-line to the low-energy beam line of the new CARIBU facility at ATLAS. CARIBU utilizes a large scale version of the same gas stopping technique described above to provide a source of very neutron-rich nuclides, produced in the fission of 252-Cf. With this new source the measurements can push even closer to the neutron drip line and provide data that are very useful for improving our models for r-process nucleosynthesis. This campaign is expected to conclude in 2014. • Subsequently, we plan to move the CPT mass spectrometer to a location in experimental area III at ATLAS to make use of the unique availability of high-intensity energetic beams of heavy nuclei, to produce very neutron-rich nuclei in regions heavier than those available through fission. These very exotic nuclei will once again be stopped in a gas catcher and presented for measurement into a newly constructed multiple-reflection time-of-flight mass spectrometer and the CPT mass spectrometer systems. This new arrangement should provide us with unique opportunities to push the boundaries of our knowledge of exotic nuclei further towards the N=126 neutron-rich region critical for the formation of the final abundance peak in the r-process. • Our original target and gas catcher system are now used to load an open geometry RFQ trap that we call the BPT. The trap is surrounded by various detectors that allow us to study beta-neutrino correlations in the decay of the trapped particles. We are examining the beta decay of the mass 8 system (8-Li and 8-B) which are sensitive individually to tensor currents, and when combined, to second class currents. • A second RFQ trap of is under construction at the CARIBU facility where it will be used to study beta-delayed neutron emission from the trapped ions. The results will delineate the decay modes of neutron-rich nuclei which play a role in nucleosynthesis. They are also relevant to understanding nuclear reactor kinetics and inform safety considerations with nuclear power plants. • Other mass measurements with trapped ions of particular interest will be undertaken as opportunities arise.

这项工作的重点是精确测量原子质量和其他性质的核远离稳定。这些结果提供了有关这些奇异区域中涉及核的核反应所释放的能量的信息。这些信息对于预测核反应的速率和路径非常重要，这些核反应为爆炸性天体物理事件提供动力，这些事件是较重元素核合成的候选者（通过rp-，nu-p-和r-过程）。它们还允许研究粒子物理学理论中的基本对称性，以及在原子核具有极端中子质子比的区域中的核结构的演变。测量是用加拿大潘宁阱质谱仪（CPT）进行的，该质谱仪与阿贡国家实验室的ATLAS加速器系统联机运行。核反应的高能产物在气室中被减慢，并在一系列离子阱中被收集、冷却和净化。然后，这种外来核素的离子云被转移到一个精密的潘宁阱中，在那里可以测量离子的质量，精确到十亿分之几。或者，离子也可以被转移到射频四极离子阱（RFID），在那里它们悬浮在氦气中。这样一团几乎处于静止状态的奇异原子核云，为研究β粒子与中微子以及衰变过程中释放出的其他粒子之间的相关性提供了一个独特的机会。·CPT已从其原来的位置移动，并在线安装到ATLAS新的CARIBU设施的低能束线。CARIBU利用上述相同气体停止技术的大规模版本来提供在252-Cf裂变中产生的非常富中子的核素的源。有了这个新的来源，测量可以更接近中子滴线，并提供数据，是非常有用的，以改善我们的模型r-过程核合成。这项运动预计将于2014年结束。随后，我们计划将CPT质谱仪移至ATLAS实验区III的一个位置，以利用重核高强度高能束的独特可用性，在比裂变更重的区域产生非常富含中子的核。这些非常奇特的原子核将再次停在气体捕集器中，并在新建造的多次反射飞行时间质谱仪和CPT质谱仪系统中进行测量。这种新的安排应该为我们提供了独特的机会，推动我们的知识边界的外来核进一步走向N=126的富中子区的形成的最终丰度峰的r-过程的关键。·我们最初的目标和气体捕集器系统现在用于加载我们称为BPT的开放几何形状的捕集器。这个陷阱被各种各样的探测器包围，使我们能够研究被困粒子衰变中的β中微子相关性。我们正在研究质量为8的系统（8-Li和8-B）的β衰变，这两个系统分别对张量电流敏感，当结合起来时，对第二类电流敏感。·第二个中子阱正在加勒比区域实验室设施建造中，将用于研究被捕获离子的β缓发中子发射。结果将描绘出在核合成中起作用的丰中子核的衰变模式。它们也与理解核反应堆动力学有关，并为核电厂的安全考虑提供信息。·其他特别感兴趣的捕获离子的质量测量将在机会出现时进行。