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

这项工作的核心是精确测量原子核的质量和远离稳定性的其他性质。这些结果提供了有关涉及这些奇异区域中的原子核的核反应释放的能量的信息。这些信息对于预测核反应的速率和路径很重要，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(通过rp-、nu-p-和r-过程)。它们还可以研究粒子物理理论中的基本对称性，以及在原子核具有极端的中子与质子比的区域中核结构的演变。测量是由加拿大彭宁陷阱质谱仪(CPT)进行的，该仪器在线操作到阿贡国家实验室的ATLAS加速器系统。核反应的高能产物在气室中减慢，并在一系列离子陷阱中收集、冷却和提纯。这些奇异的核素离子云然后被转移到一个精密的彭宁陷阱，在那里离子的质量可以被测量到十亿分之几的精度。或者，离子也可以转移到射频四极离子陷阱(RFQ)，在那里它们悬浮在氦气中。这种几乎处于静止状态的奇异核云为研究β粒子与中微子和衰变过程中发射的其他粒子之间的相关性提供了一个独特的机会。已计划或正在采取下列举措：·CPT已从原址移至ATLAS新的Cariu设施的低能束线，并已在线安装。Cariu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含中子的核素的来源。有了这个新的源，测量可以更接近中子滴线，并提供对改进我们的r-过程核合成模型非常有用的数据。这场运动预计将于2014年结束。·随后，我们计划将CPT质谱仪转移到ATLAS实验区III的一个位置，以利用重核的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丰富的中子核。这些非常奇怪的原子核将再次被阻止在气体捕集器中，并被送到新建造的多反射飞行时间质谱仪和CPT质谱仪系统中进行测量。这一新的安排应该为我们提供独特的机会，将我们关于奇异核的知识的边界进一步推向N=126丰中子区，这对r过程中最终丰度峰的形成至关重要。·我们最初的目标和气体捕集器系统现在被用来装载一个开放的几何RFQ陷阱，我们称之为BPT。陷阱周围环绕着各种探测器，使我们能够研究被捕获粒子衰变过程中的贝塔-中微子关联。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，当组合在一起时，对第二类电流敏感。·Cariu设施正在建造第二个RFQ陷阱，将在那里用于研究捕获离子的贝塔延迟中子发射。这些结果将描绘在核合成中起作用的富中子核的衰变模式。它们也与理解核反应堆动力学有关，并为核电站的安全考虑提供信息。·当机会出现时，将对特别感兴趣的囚禁离子进行其他质量测量。

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.