Ultrafast Nanodosimetry - the role of the nanoscale in radiation interactions in matter.

随着基于辐射的技术继续以对工艺和应用进行更严格的控制为目标，我们对材料如何在最小范围内对辐射做出反应的理解上的限制正在成为进步的障碍。随着中央激光设施的极端光子应用中心定于2024年投入使用，现在越来越需要开发必要的方法来在纳米尺度上询问和理解这些相互作用，以加速这一新的国家能力将开启的下一波创新浪潮。在“超快纳米碘测量学”中，我们将通过研究超快过程和电离辐射相互作用的物质纳米结构之间的相互作用来应对这一挑战。目前，在扩展长度尺度上运行的应用模型中，标准做法是假设物质在纳米尺度上均匀或均匀分布。这是因为在扩展体积中包括这种典型的疾病在计算上将非常昂贵。此外，均匀近似精确地预测了入射辐射在介质中损失能量的范围，使其成为一种通用而有效的方法。然而，尽管射程对应用来说当然很重要，但电离物种通过所造成的辐射化学和永久性损害也同样重要。例如，由于制造需要更高的精度，例如量子点发光二极管的离子诱导缺陷，显然将达到一个极限，在那里理解纳米结构依赖的工艺将是匹配这些雄心的关键。此外，即使是像放射治疗这样的宏观应用，也将越来越依赖于了解纳米放射化学路径，例如，使用金纳米颗粒剂量增强治疗开辟通往患者特定模式的路径。因此，我们必须开始建立一幅关于能量如何在纳米尺度上在辐照物质中储存和传输的全面图景。我们认为，在纳米尺度上持续存在的过程对纳米尺度的异质性高度敏感，因此，对于在预测框架中充分理解这些相互作用至关重要。这一假设是基于最近对物质中超快质子相互作用的实验，这些实验质疑了静态、均匀密度分布的假设。测试这一点将通过利用激光驱动加速器的独特能力来实现，该加速器从单一来源提供X射线和质子的超快脉冲。这两个物种在物质上有着根本不同的相互作用，我们将利用这些相互作用来询问受辐射系统中的“本地”和“非本地”过程。这可以理解为以下几点。如果初级电离电子具有高能量(即那些由X射线激发的电子)，它们平均而言将在第一次碰撞之前远离电离点。在这种情况下，他们看不到材料的局部纳米结构，初始剂量迅速变得均匀(非局部)。相反，如果初级电子的能量较低(即由质子激发的电子)，它们在第一次碰撞之前不会移动很远。在这种情况下，它们将在初始电离点(局部)附近与材料相互作用，成为纳米结构的探测器。我们将与我们在德国的合作伙伴中国和美国一起开发跟踪这些过程的新方法。特别是，我们的目标是展示异质性如何通过在纳米尺度上调节物质的结构来影响远离平衡的物质的动力学。这将为当前“同质”模式的崩溃提供一个硬性限制。我们的首要目标是揭示纳米过程如何影响复杂系统中的宏观现象和能量传输。

As radiation-based technologies continue to target tighter controls over processes and applications, limits in our understanding of how materials respond to irradiation on the very smallest scales is becoming a barrier to progress. With the commissioning of the Extreme Photonics Applications Centre at the Central Laser Facility due in 2024, there is now a growing need to develop the methodologies required for interrogating and understanding these interactions on the nanoscale to accelerate the next wave of innovation that will be unlocked by this new national capability. In 'Ultrafast Nanodosimetry' we will address this challenge by investigating the interplay between ultrafast processes and the nanoscopic structure of matter for ionising radiation interactions. Currently, in models for applications that operate over extended length scales it is standard practice to assume that matter is evenly, or uniformly, distributed on the nanoscale. This is because including the disorder typical in extended volumes would be computationally very expensive. Also, the uniform approximation accurately predicts the range over which the incident radiation loses energy in the medium, making this a versatile and efficient approach. However, while range is certainly important for applications, the radiation chemistry and permanent damage caused by the passage of ionising species is equally important. For instance, as manufacturing demands greater precision e.g. ion-induced defects for quantum dot light emitting diodes, it is clear that a limit will be reached where an understanding of nanostructure-dependent processes will be crucial to match these ambitions. Furthermore, even macroscopic applications such as radiotherapy will increasingly rely on understanding nanoscopic radiation chemistry pathways to open, for example, routes towards patient-specific modalities using gold nanoparticle dose-enhanced treatments. Therefore, it is essential that we begin to build a comprehensive picture of how energy is deposited and transported on the nanoscale in irradiated matter. We propose that there are processes that persist on the nanoscale that are highly sensitive to nanoscopic heterogeneity and, as such, are crucial for fully understanding these interactions in a predictive framework. This hypothesis is based on recent experiments examining ultrafast proton interactions in matter that have called into question the assumption of a static, uniform density distribution. Testing this will be achieved by harnessing the unique capability of laser-driven accelerators to provide ultrafast pulses of both X-rays and protons from a single source. Both of these species have fundamentally different interactions in matter that we will exploit to interrogate both 'local' and 'non-local' processes in irradiated systems. This can be understood as follows. If the primary ionised electrons have high energy (i.e. those excited by X-rays), they will, on average, travel far from the point of ionisation before their first collision. In this case they do not 'see' the local nanostructure of the material and the initial dose becomes rapidly homogenous (non-local). Conversely, if the primary electrons have low energy (i.e. those excited by protons), they will not travel far before their first collision. In this case they will interact with the material near the point of initial ionisation (local), becoming a probe of nanostructure. Together with our partners in Germany, China and the US we will develop new methods to track these processes. In particular, we aim to show how heterogeneity can influence dynamics in matter far from equilibrium by tuning the structure of matter on the nanoscale. This will provide a hard limit for which current 'homogenous' models break down. Our overarching goal is to reveal how nanoscopic processes can influence macroscopic phenomenology and energy transport in complex systems.