Beta-delayed neutrons for astrophysics: Understanding the most neutron-rich nuclides

天体物理学中的β延迟中子：了解中子最多的核素

• 批准号: SAPIN-2019-00030
• 负责人: Dillmann, Iris
• 金额: $ 10.42万
• 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: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=764738
• 关键词: Beta; delayed; neutrons; astrophysics; Understanding

A large fraction of the heavy nuclei (elements heavier than iron) that are produced in the "rapid neutron capture process" (r process) are not (yet) experimentally accessible and are located in the so-called "Terra Incognita". With the next generation of radioactive ion beam (RIB) facilities presently under construction worldwide, the main motivation of all projects is the investigation of these very neutron-rich nuclei which are in or at the reaction path of the r process. However, until the new facilities will become operational within the next 5-10 years, the presently operating facilities are continuing to push the borders of known nuclei as far out as possible. Whereas the proton dripline has been reached for many elements up to mass A~200, the neutron dripline is only accessible up to A~40 (Na, Mg). Theoretical predictions show that on top of the 3000 known nuclei one can expect ~4000 more nuclei to be discovered, the largest fraction of them on the neutron-rich side. For these neutron-rich nuclei, a new decay mechanism appears when the neutron separation energy is lower than the reaction Q value: beta-delayed neutron (bdn) emission. Two important physical quantities can be measured with the investigation of bdn emitters: the beta-decay half-life and the beta strength above the neutron separation energy from the neutron-branching ratio. The more neutron-rich a nucleus becomes, the more important bn emission gets until it will be the dominant decay mechanism for almost all newly discovered neutron-rich nuclei. So far about 600 bn-emitters are known, but for only 300 of them the neutron-branching ratio has been measured. In 2016/17 we have (re)measured 270 bn-emitters alone in the BRIKEN campaign. For 183 of them (68%) the neutron-branching ratio was measured for the first time, and for 60 of them the beta-decay half-life for the first time. With this proposal I will continue and extend my ongoing program about the investigation of even more exotic bdn emitters in the next 5 years. In 2019/20 we are planning to run at least three more experiments at RIKEN, one led by my group. These measurements are aiming at a better understanding of the competition between delayed one- and multi-neutron emission. In addition, we will provide data for the very rare processes of delayed three- and four-neutron emission. After the BRIKEN campaign we aim to extend our experimental scope by moving our detection setup to another facility to try to investigate yet inaccessible nuclei like e.g. heavy isotopes at the N=126 shell closure with the multi-nucleon transfer. This promising reaction mechanism will allow for the first time access to those nuclei that are responsible for the third peak of the r-process around mass A~195. A detailed knowledge of the bdn process is an important key ingredient for a better understanding of even more neutron-rich nuclei that will not be accessible experimentally and have to be inferred from theoretical models.

在“快速中子捕获过程”（R过程）中产生的重核的大部分（元素比铁重）尚未在实验上访问，并且位于所谓的“ Terra Incognita”中。随着下一代的放射性离子束（肋骨）设施目前正在全球范围内，所有项目的主要动机是对R过程中或反应路径中的这些非常中子的核进行研究。但是，直到新设施在未来5 - 10年内将在运营中运作，目前的运营设施将继续将已知核的边界推到尽可能远的地方。尽管已经达到了质子滴度的许多元素，直到质量为〜200，但中子滴液只能达到〜40（Na，mg）。理论上的预测表明，在3000个已知核的基础上，人们可以期望发现更多的核，这是其中最大的核心，其中最大的是富含中子的一侧。对于这些富含中子的核，当中子分离能低于反应Q值时，出现了一种新的衰减机制：脱离β的中子（BDN）发射。通过研究BDN发射器可以测量两个重要的物理量：beta-decay的半衰期和比中子分支比率高于中子分离能的β强度。 核变得越富含中子，BN发射就越重要，直到它成为几乎所有新发现的中子核的主要衰减机制。到目前为止，已知大约600个发射机，但只有300个中子分支比率已经测量了。在2016/17年度，我们（重新）仅在Briken运动中仅测量了270个emerters。对于其中183个（68％），首次测量了中子分支率，其中60个是β-贝塔赛半衰期。 通过这项提议，我将继续进行我正在进行的有关在未来5年内调查更多异国情调的发射器的计划。在2019/20年，我们计划在Riken进行至少三个实验，这是由我的小组领导的。这些测量结果是更好地了解延迟的一单中性和多内部排放之间的竞争。此外，我们将为延迟的三中音和四个中子发射的非常罕见的过程提供数据。 在布里肯运动之后，我们旨在通过将检测设置转移到另一个设施，以尝试调查像E.G. n = 126壳的重型同位素闭合，多核子转移。这种有前途的反应机制将首次允许那些在质量A 〜195左右导致R-Process的第三个峰的核。对BDN过程的详细知识是更好地理解更多富含中子的核的重要关键成分，而这些核将无法实验，并且必须从理论模型中推断出来。