Modelling the electron anti-neutrino flux from nuclear reactors

自从20世纪50年代的Cowan-Reines实验首次对中微子进行实验检测以来，核试验反应堆作为电子反中微子的来源，在中微子物理学领域发挥了核心作用。这些电子反中微子可以通过反衰变反应[1]探测到，它们是由核内主要锕系元素裂变形成的富中子核的衰变产生的。因此，这种电子反中微子通量本质上与反应堆的运行有关，并与反应堆的功率和堆芯的可裂变库存有关。考虑到对反应堆运行参数和可裂变库存的依赖，利用中微子监测反应堆的概念已经存在了一段时间，但直到最近，人们对中微子的理解才使这种前景成为可能。与目前的国际原子能机构程序相反，基于反中微子的安全保障允许对核燃料进行批量核算，产生对生产的裂变材料质量的估计，而不需要对项目的质量进行假设。此外，反中微子方法是非侵入性的，通过在离反应堆很远的地方使用探测器来进行，并允许对堆芯进行实时测量。在不久的将来，利用这项技术最合理的期望是在10米的距离上部署吨级便携式反中微子探测器。在这些距离上，中微子振荡实验已经证明，与在更大距离上运行的探测器相比，中微子消失对通量的影响要小得多，比如在卡姆兰实验b[5]中。虽然通过中微子探测对核反应堆进行远场监测是一种理想的前景，但中微子混合的贡献和光谱背景的增加大大增加了所需建模的复杂性。电子反中微子能谱用于反应堆监测的目的依赖于与预期通量和能谱的偏差。因此，需要将预期通量和能谱的模型与测量速率进行比较，通过统计方法，可以建立与模型显著偏离的阈值，以及检测这种偏离所需的时间范围[10]。这种反中微子模型很可能成为反中微子物理学论文的主要基础。这将包括根据核反应堆（如哈特尔普尔）提供的运行数据，以及乏燃料库存，为反应堆生成反中微子源项。这些源项将被量化，包括提供在不同距离上入射到探测器的通量的估计，考虑到这种通量的中微子混合以及实时核芯的预期演化等现象，现有的应用程序，如地源中微子[7]，没有考虑到这一点，因此可能用于通知此类软件。除此之外，还有几个途径可供进一步探索。这些现象包括在5兆电子伏左右检测到的反中微子的意外过量，原因不明，一些人推测这是由于中微子引起的氘核解体或相干弹性中微子核散射[8]等可能性。另一个进一步的反常现象可能有助于研究，那就是在短基线实验中预期的反应堆反中微子事件的下降参考文献[1]Cowan， C, Reines， F, Harrison， F, Kruse， H.和McGuire， A., 1956。自由中微子的探测：确认。科学，124(3212)，第103- 104页。[10]本波拉德，C，格拉塔，G.和沃格尔，P., 2002。基于反应堆的中微子振荡实验。现代物理学报，32 (2),pp.297- 298博登，n.n。反应堆monitori

Since the first experimental detection of the neutrino, with the Cowan-Reines experiment in the 1950s,nuclear test reactors have played a central role within the field of neutrino physics as a source of electronanti-neutrinos. These electron anti-neutrinos can be detected through an inverse beta decay reaction:[1] and arise from the beta decay of neutron rich nuclei formed by the fission of majoractinides within the core. As a result, this electron anti-neutrino flux is inherently tied to the operation ofa reactor, and related to the power of the reactor and the fissile inventory of its core [2].Given the dependence on the operational parameters and fissile inventory of a reactor, the concept of utilisingneutrinos to monitor reactors has existed for some time, but it is only recently that the understanding of thehas made such prospects feasible [3]. In contrast to current IAEA procedures, anti-neutrino based safeguardsallow for bulk accountancy of nuclear fuel, yielding an estimate of the masses of fissile material producedwithout necessitating assumptions regarding the mass of items. Additionally, anti-neutrino methods arenon-invasive, being carried out through use of a detector at a standoff distance from the reactor and allowfor real time measurement of the core.In the near future, the most reasonable expectation for the utilisation of this technology is through thedeployment of tonne-scale portable anti-neutrino detectors at a standoff distance of the order of 10 metres.At these distances, neutrino oscillation experiments have demonstrated the vastly reduced effects of neutrinodisappearance on the flux compared to detectors operating at far greater standoff distances, such as in theKamland experiment [4] [5]. Whilst far field monitoring of nuclear reactors through neutrino detection is adesirable prospect, the contributions of neutrino mixing and the increased background of the spectra greatlyincrease the complexity of modelling required.Use of the electron anti-neutrino spectra for the purposes of reactor monitoring is reliant on deviationsfrom an expected flux and energy spectra. Thus, models of an expected flux and energy spectra are neededin comparison with the measured rate, where through statistical methods, a threshold for a significant deviationfrom the model, and the time frame needed to detect this deviation, can be established [6].This anti-neutrino modelling is likely to form the main underpinning of a thesis in anti-neutrino physics.This will include generation of anti-neutrino source terms for reactors based on operational data providedfrom nuclear reactors, such as Hartlepool, along with spent fuel inventories. These source terms will bequantified to include to provide an estimation of the flux incident to a detector at varying distances, consid-1ering phenomena such the neutrino mixing of this flux along with the expected evolution of a nuclear core ona real time basis, something that existing applications, such as geo-neutrinos [7], do not consider and mighttherefore be used to inform such software.Beyond this, several avenues exist for further pursuit. These include phenomena such as the unexpectedexcess of anti-neutrinos detected at around 5 MeV with an unknown cause, speculated by some to be due topossibilities such as neutrino induced deuteron disintegration or coherent elastic neutrino-nucleus scattering[8]. Another, further, anomaly that may lend itself to investigation is that of the drop in expected reactoranti-neutrino events in short baseline experiments [9].2 References[1] Cowan, C., Reines, F., Harrison, F., Kruse, H. and McGuire, A., 1956. Detection of the Free Neutrino:a Confirmation. Science, 124(3212), pp.103- 104.[2]Bemporad, C., Gratta, G. and Vogel, P., 2002. Reactor-based neutrino oscillation experiments. Reviewsof Modern Physics, 74(2), pp.297-328.[3] Bowden, N., 2008. Reactor monitori