Towards nuclear astrophysics measurements at the NEW Birmingham High-Flux Accelerator-Driven Neutron Facility (HF-ADNeF)

中子是存在于原子核心紧密结合的原子核中的不带电粒子。它们和带电的质子一起构成了我们周围的大部分物质。在宇宙中，我们在地球上发现的大多数元素都是在恒星中通过中子捕获和随后的β衰变的结合产生的。这些过程将巨星中的轻元素转化为重元素，这些巨星的大小是太阳的许多倍。在这样的环境中，每平方厘米每秒可能有数十亿个中子穿过。虽然这听起来像是一个巨大的数字，但元素捕获中子的概率，即使在这样的环境中，也是相当低的，因此它被称为慢中子捕获过程，或简称为s过程。关于s过程，我们还有很多不了解的地方，比如，s过程在哪里分成几个分支的细节，衰变过程的精确速率等等。这些知识上的空白意味着我们不能完全理解元素是如何形成的（核合成），以及巨星中每种元素的丰度是多少——地球就是由这些物质形成的。为了找到答案，我们可以在实验室中研究s过程来测量缺失的信息。然而，因为中子是不带电的，所以不可能用电场和磁场来加速它们。这使得用于研究的中子束更难产生。然而，在伯明翰，我们正在建造下一代中子源，通过用质子轰击锂靶来产生中子。这台机器将于2022年初投产。产生的中子的能量将与巨大恒星中的能量非常相似。此外，新中子束的强度将是世界上同类中最高的之一（每秒能够产生超过10万亿个中子）。这种能量和强度的独特组合使得研究s过程成为可能。为了促进这些研究，这个建议是测试建造一个探测器端站的可行性，这个端站有足够好的屏蔽，探测器不会被中子束损坏。增加的复杂性是中子束需要聚焦到一个反应目标上，而不能显著降低中子束的强度。靶和中子之间的反应可以被观察和测量。为了充分利用这个难得的机会来探索建立英国天体物理实验室的潜力，需要在机器安装后进行可行性研究。

Neutrons are uncharged particles that exist in the tightly bound nucleus at the core of atoms. Together with charged protons they make up most of the mass that we see around us. In the Universe, most of the elements that we find on earth have been produced in stars by a combination of neutron capture and subsequent beta decay. These processes convert light elements to heavier elements in giants stars - those many times the size of our sun. In such environments there can be billions of neutrons passing through every square centimetre every second. Although this sounds like a huge number, the probability of elements capturing neutrons, even in such an environment, is quite low and so it is referred to as the slow-neutron capture process - or s-process for short. There are many things we don't understand about the s-process, for example, details about where the process splits into several branches and the precise rates of the beta decay process etc. These gaps in our knowledge mean we don't have a full understanding of how the elements were made (nucleosynthesis) and what the abundances of each element in giant stars were - material from which the earth was formed. To find out, we can study the s-process in the laboratory to measure the missing information. However, because neutrons are uncharged, it is not possible to accelerate them using electric and magnetic fields. This makes beams of neutrons for research more difficult to produce. However, at Birmingham we are building a next-generation neutron source that generates neutrons by bombarding a lithium target with protons. This machine will come on line in early 2022. The energies of the neutrons produced will closely mimic those found in giant stars. Furthermore, the intensity of the new neutron beam will one of the highest of its kind in the world (capable of producing more than a 10 trillion neutrons per second). This unique combination of energy and intensity makes the study of the s-process possible. To facilitate these studies, this proposal is to test the feasibility of building a detector end-station that is sufficiently well shielded that the detectors won't be damaged by the neutron beam. The added complexity is that the neutron beam needs to be focused on to a reaction target without diminishing the intensity of the beam significantly. The reactions between the target and neutrons could then be observed and measured.To fully exploit this rare opportunity for exploring the potential of making a UK laboratory for astrophysics requires undertaking this feasibility study when the machine is installed.