MRI: Development of a Separator for Capture Reactions (SECAR) Phase 2

众所周知，原子核是由质子和中子组成的。正如核科学咨询委员会所确定的，核科学中的一个悬而未决的问题是：元素的起源是什么？要产生具有多个中子和质子的原子核，需要在恒星中发生一系列核反应。要产生比铁更重的原子核，需要一个高能环境，如超新星爆炸或中子星合并。即将在这里建造的设备--分离俘获反应(SECAR)光谱仪--将使国家超导回旋实验室(NSCL)的物理学家能够测量罕见的核反应，这些反应对于了解元素的起源是必要的。这里计划的SECAR光谱仪第二阶段将成为用于这一目的的世界领先设施。它能够测量X射线爆发中的整个重要反应范围，X射线爆发是我们银河系中观察到的最常见的热核爆炸。X射线爆发发生在质量吸积中子星的表面。利用SECAR第二阶段的数据，爆发观测可以用来探测中子星和X射线双星系统的性质。此外，可以对形成中子星外壳的元素进行预测，这些元素也可能部分被喷射到太空中。SECAR第二阶段还将能够预测天体物理新星爆炸的元素特征，特别是可能在不久的将来用新望远镜观察到的异常高能事件。这将有助于在观测数据中以及在地球上发现的陨石颗粒的组成中识别这些事件的特征。SECAR第二阶段的数据还将有助于理解超新星中放射性元素的产生，早期宇宙中存在的最大质量恒星的特征，超新星中微子风对元素起源的贡献，并有助于证明或反驳索恩-齐特科夫天体的存在，索恩-齐特科夫天体是假设的恒星对象，其核心包含一颗中子星。

It is well known that nuclei are made from protons and neutrons. One of the open questions in nuclear science, as identified by the Nuclear Science Advisory Committee, is: what is the origin of the elements? To produce nuclei having more than a few neutrons and protons requires a sequence of nuclear reactions that take place in stars. To produce nuclei heavier than iron requires a highly energetic environment, such as a supernova explosion or a neutron star merger. The equipment to be built here, the Separated Capture Reaction (SECAR) spectrometer, will enable physicists at the National Superconducting Cyclotron Laboratory (NSCL) to measure rare nuclear reactions that are necessary to understand the origin of the elements. Phase 2 of the SECAR spectrometer, planned here, will become a world-leading facility for this purpose.SECAR Phase 2 opens a wide range of science opportunities. It enables measurements of the entire range of important reactions in X-ray bursts, the most common thermonuclear explosions observed in our Galaxy. X-ray bursts occur on the surface of mass-accreting neutron stars. With the SECAR Phase 2 data, burst observations can be used to probe the properties of neutron stars and X-ray binary systems. In addition, predictions can be made of the elements created that form the crust of the neutron star and may also, in part, be ejected into space. SECAR Phase 2 will also enable predictions of the element signatures of astrophysical Nova explosions, especially unusually energetic events that may be observed with new telescopes in the near future. This will help to identify the signatures of these events in observational data, and in the composition of meteoritic grains found on earth. SECAR Phase 2 data will also help understand the production of radioactive elements in supernovae, the signatures of the most massive stars ever that existed in the early universe, the contribution of supernova neutrino winds to the origin of the elements, and help prove, or disprove, the existence of Thorne-Zytkov objects, hypothetical stellar objects that contain a neutron star as their core.