Beta-delayed neutron measurements for nuclear astrophysics

核天体物理学的β延迟中子测量

• 批准号: SAPIN-2014-00028
• 负责人: Dillmann, Iris
• 金额: $ 8.74万
• 依托单位: TRIUMF
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=612386
• 关键词: Beta; delayed; neutron; measurements; nuclear

Beta-delayed neutron emitters play an important, two-fold role in the stellar nucleosynthesis of heavy elements in the "rapid neutron-capture process" (r process). On one hand they lead to a detour of the material beta-decaying back to stability. On the other hand, the released neutrons increase the neutron-to-seed ratio, and are re-captured during the freeze-out phase and thus influence the final solar r-abundance curve. Two important physical quantities can be measured at once with bn-emitters: the half-life of the precursor, and the beta-strength above the neutron separation energy can be deduced from the neutron-branching ratio. A large fraction of the isotopes inside the r-process reaction path are not yet experimentally accessible and are located in the (experimental) "Terra Incognita". With the next generation of fragmentation and ISOL facilities presently being built, one of the main motivation of all projects is the investigation of these very neutron-rich isotopes. Presently, about 600 one-neutron emitters are known, but only for a third of them experimental data is available. However, reaching more neutron-rich isotopes means also that multiple neutron-emission becomes the dominant decay mechanism. About 460 beta-delayed two-, three- or four-neutron emitters are identified up to now but for only 30 of them experimental data about the neutron branching ratios are available, most of them in the light mass region below A=30. The International Atomic and Energy Agency (IAEA) has identified the urgency and picked up this topic recently in a 4-year “Coordinated Research Project" on a “Reference Database for Beta-Delayed Neutron Emission Data”. This project will review, compile, and evaluate the existing data for neutron-branching ratios and half-lives of beta-delayed neutron emitters. This will help to ensure a reliable database for the future discoveries of new isotopes and help to constrain astrophysical and theoretical models. TRIUMF has taken a lead role in this and has submitted an extensive proposal with Canadian colleagues from McMaster University and the University of Guelph for future measurements and the evaluation of existing data. This Discovery Grant application aims to investigate beta-delayed neutron-emitters with several detectors and novel techniques at different world-leading facilities. One direction is the use of the “standard” method with 3He-filled neutron detectors to measure directly the branching ratio and half-lives. This research will be conducted with highly-efficient detector setups and state-of-the-art electronics. The "BRIKEN campaign" at RIKEN/ Japan proposes to perform experiments in 2014-16 with the most efficient neutron detector setup worldwide. Under my leadership TRIUMF is involved in this campaign and will submit proposals for measurements on astrophysical key nuclides. After the BRIKEN campaign the existing program at the present ISAC-1 facility at TRIUMF will be extended towards more neutron-rich beams which are expected with the new ARIEL facility in a few years. We propose to carry out high-precision branching-ratio measurements for nuclear structure and r-process studies. The second direction is the development of novel techniques to measure neutron-branching ratios circumventing the detection of the neutron. One of the proposed methods uses traps to measure the branching ratio and neutron energy spectra via the beta-recoil ion coincidence technique. This method has recently been successfully employed by an Argonne/ Livermore collaboration. The advantages and disadvantages of this method will be investigated with both traps at TRIUMF (TITAN and TRINAT). The additional installation of neutron detectors can expand this method to multi-neutron emitters.

在“快速中子捕获过程”（r过程）中，占主元的中子发射器在重元素的恒星核共相性中起着重要的，两倍的作用。一方面，它们导致绕过材料的beta账面，以恢复稳定性。另一方面，释放的中子会增加中子与种子的比率，并在冷冻阶段重新捕获，从而影响最终的太阳R-充血曲线。可以用BN发射器立即测量两个重要的物理量：前体的半衰期，并且可以从中子分支比率中推导出中子分离能的β-强度。 R过程反应路径内部的大部分同位素尚未实验可访问，并且位于（实验性的）“ Terra Incognita”中。由于目前正在建造下一代的分裂和孤立设施，所有项目的主要动机之一是这些非常中子的同位素的投资。目前，已知大约600个单中子发射器，但只有三分之一的实验数据可获得。但是，达到更多富含中子的同位素也意味着多个中子排放成为主要的衰减机制。到目前为止，大约有460张Beta延迟的两，三中或四个中子发射器已确定，但是对于中子分支比率中只有30个实验数据，只有30个实验数据可用，其中大多数在A = 30以下的光质量区域中。 国际原子能机构（IAEA）已确定了紧迫性，最近在“β-删除中子排放数据的参考数据库”上的4年“协调研究项目”中提到了这一主题。该项目将审查，编译和评估现有数据的中子分支比率和半衰期为beta的中子发射器的半衰期。这将有助于确保新同位素的未来发现的可靠数据库，并有助于限制天体物理和理论模型。 Triumf在这方面发挥了领先作用，并向麦克马斯特大学和圭尔夫大学的加拿大同事提出了广泛的提议，以进行未来的测量和现有数据的评估。 该发现赠款应用程序旨在通过不同的世界领先设施来调查使用多个探测器和新技术的中子发射器研究。 一个方向是将“标准”方法与3HE填充的中子探测器一起使用直接测量分支比和半衰期。这项研究将使用高效的检测器设置和最先进的电子设备进行。 Riken/ Japan的“ Briken运动”提议在2014 - 16年度进行实验，并在全球范围内设置最有效的中子探测器设置。在我的领导下，凯旋（Triumf）参与了这项运动，并将提交有关天体物理主要核心素的测量的建议。 布里肯（Briken）运动之后，现有的ISAC-1设施的现有计划将扩展到更多的中子横梁，预计新的Ariel设施将在几年内使用。我们建议对核结构和R过程研究进行高精度分支比率测量。 第二个方向是开发新技术，以测量中子的中子分支比的检测。提出的方法之一使用陷阱通过β循环离子重合技术来测量分支比和中子能谱。该方法最近已被Argonne/ Livermore合作成功地使用。该方法的优点和缺点将通过Triumf（Titan和Trinat）的两个陷阱进行研究。中子探测器的附加安装可以将此方法扩展到多个中子发射器。