Symmetry-restored two-centre self-consistent approach to fission with arbitrary deformations, orientations, and distance of fragments

这个提议的愿景是将最先进的理论思想和计算引入核裂变物理学。自从近80年前发现裂变以来，积累了丰富的实验数据。这一直伴随着自发和诱导裂变的有效现象学和显微镜的发展。然而，几乎所有这些研究都依赖于假设裂变的绝热性和/或热化。能量足够低，时间足够长，这些假设成立吗？该项目的目标是实现裂变的理论建模，为这些挑战提供明确的答案。从外面看，裂变看起来像一个简单的过程，一滴物质分裂成两个或更多更小的液滴。然而，这是非常误导的：在液滴分裂和核裂变之间存在着巨大的概念差距。简而言之，在裂变过程中，一个复合量子系统分裂成两个或更多个复合量子系统，并且这样一个过程的所有性质都关键地取决于量子物理，这不是经典液滴的情况。在这里，核子在相关量子轨道中移动，这些轨道在裂变碎片中演化成相关量子轨道。总之，在裂变中，我们发现了中观系统的所有美丽和困难。裂变发生在经典与量子、大与小、慢与快现象之间的边界区域。这就是为什么它是如此具有挑战性，从而提供了一个重要的基础科学研究课题。目前，用于描述在不同的激发能量诱导裂变的方法是在一个非常初级的状态。标准框架可以追溯到玻尔和惠勒在1939年的开创性工作，即在共振中子俘获后产生的热化复合核。然而，将这一概念应用于其他创造裂变前状态的机制并不是真正正确的方法。事实上，在前体系统的β衰变、光子吸收、通过电荷的库仑激发或粒子转移之后，原子核最终处于一个相当确定的中间“门口”状态，然后裂变。根据激发能量和裂变时间尺度的不同，这种中间态可能有也可能没有足够的时间热化，那么复合核的概念就变得非常可疑。一个挑战裂变理论主要范式的完整研究计划将需要大量的人力和资源投资。目前的建议旨在提供这样一个方案的一个基本计算要素，即计算机代码，该代码将允许在任意变形、定向和碎片距离的裂变的双中心自洽方法内求解核DFT方程。这里的主要挑战是使用新的非局域密度泛函进行有效的裂变计算，这是核DFT的当前发展的中心。使用这个工具，在未来，我们将能够通过使用含时密度泛函理论（DFT）的高能振动极限来明确地构建门口状态，然后跟踪裂变，其中包括与这种振动的耦合。这个完整的计划将重新定义裂变的未来研究。我们不能再依赖旧的想法和简化。目前，没有一个预测裂变寿命超过绝热极限存在。如果能证明这是有可能实现的，这本身就是一个重要的研究突破。为了表明没有绝热性或热化的结果是根本和定性的不同，将导致一个全新的方法，以未来的研究。

The vision of this proposal is to bring into the physics of nuclear fission the most advanced theoretical ideas and computation. Since the discovery of fission almost eighty years ago, a wealth of experimental data has been accumulated. This has been accompanied by the development of an efficient phenomenology and microscopy of spontaneous and induced fission. However, almost all of these studies rely on assuming the adiabaticity and/or thermalisation of fission. Is the energy sufficiently low and time sufficiently long for these assumptions to hold? This project has the ambition to implement theoretical modelling of fission that will deliver definite answers to these challenges. From the outside, fission looks like a simple process where a single drop of matter splits into two or more smaller drops. However, this is very misleading: a huge conceptual gap exists between the splitting of liquid drops and nuclear fission. Briefly, during the fission process, one composite quantum system splits into two or more composite quantum systems, and all properties of such a process crucially depend on quantum physics, which is not the case for the classical liquid drop. Here, nucleons move in correlated quantum orbitals that evolve into correlated quantum orbitals within the fission fragments. Altogether, in fission we find all the beauty and difficulty of a mesoscopic system. The fission happens in the border region between classical and quantal, large and small, and slow and fast phenomena. This is why it is so challenging and consequently provides an important subject of fundamental science research.Currently, the methodology used for describing induced fission at varying excitation energies is in a very rudimentary state. The standard framework, dating all the way back to the pioneering work of Bohr&Wheeler in 1939, is that of a hot thermalized compound nucleus, which is created after resonant neutron capture. However, applying this concept to the other mechanisms of creating pre-fission states is not really the right way to proceed. Indeed, after the beta-decay of a precursor system, photon absorption, Coulomb excitation by a passing charge, or particle transfer, the nucleus ends up in a fairly well determined intermediate "doorway" state, which then fissions. Depending on the excitation energy and fission time scale, such an intermediate state may or may not have enough time to thermalize, and then the very concept of a compound nucleus becomes highly questionable.A full research programme to challenge the main paradigms of the theory of fission would require a substantial investment in the workforce and resources. The current proposal aims to deliver one fundamental computational element of such a programme, namely, the computer code that would allow for solving the nuclear DFT equations within the symmetry-restored two-centre self-consistent approach to fission with arbitrary deformations, orientations, and distance of fragments. The main challenge here is to perform efficient fission calculations using novel nonlocal density functionals, which are in the centre of current developments of the nuclear DFT. Using this tool, in the future, we will be able to build the doorway states explicitly, by employing the high-energy vibrational limit of the time-dependent density functional theory (DFT), and then to follow the fission with coupling to such vibrations included. This full programme will redefine future research of fission. We cannot anymore rely on the old ideas and simplifications. At present, not a single prediction of fission lifetimes beyond the adiabatic limit exists. To show that this is actually possible to obtain, would be in itself an important breakthrough in research. To show that without adiabaticity or thermalisation the results are fundamentally and qualitatively different, would lead to an entirely new approach to future research.