Ultra-short and tuneable positron beams for high-resolution and volumetric inspection of materials

亚微米缺陷代表了制造中众所周知的基本问题，因为它们显著影响几乎任何高价值组件的性能和寿命。即使是小规模的缺陷也会对高性能和高价值组件的性能和寿命产生巨大影响，特别是在恶劣环境中制造和需要在恶劣环境下执行时。高温高压处理、新的焊接方法、辐射暴露、冲击损伤等都是在先进制造或极端性能使用过程中可能在材料中留下亚微米缺陷的情况。正电子湮没寿命谱（帕尔斯）可以说是最成功的材料非侵入性检测和小尺度缺陷识别技术之一。与其他检测技术相比，帕尔斯具有几个独特的优势：它几乎适用于任何类型的材料（晶体和非晶体，有机和无机，生物和非生物），它甚至可以识别浓度低至百万分之一的亚纳米缺陷，并且可以提供有关缺陷类型及其特征尺寸的信息。帕尔斯已在涡轮机、聚合物、半导体器件、仿生系统、沸石和太阳能电池等多种测试系统中得到应用。然而，帕尔斯主要受到两个主要限制：1）可用的正电子能量限于几keV，仅允许表面研究，以及2）正电子聚束持续时间相对较长，强烈影响该技术的分辨率。利用激光等离子体粒子加速的最新进展，它建议在这里开发一种新的激光驱动源的MeV级正电子束，将允许，第一次，体积和高分辨率扫描的散装材料。激光驱动的正电子束的短持续时间（~ 10 s的ps）也将允许这种技术的分辨率的阶跃变化改进。

Sub-micron defects represent a well-known fundamental problem in manufacturing since they significantly affect performance and lifetime of virtually any high-value component. Even small-scale defects can have a dramatic effect in the performance and lifetime of high-performance and high-value components, especially when made in, and required to perform under, hostile environments. Heat and pressure treatments, new welding methods, radiation exposure, impact damage, are all examples of scenarios that can leave sub-micron defects in materials during advanced manufacturing or extreme performance use.Positron Annihilation Lifetime Spectroscopy (PALS) is arguably one of the most successful techniques for the non-invasive inspection of materials and identification of small-scale defects. PALS presents several unique advantages compared to other inspection techniques: it works virtually with any type of material (crystalline and amorphous, organic and inorganic, biotic and abiotic), it can identify even sub-nanometer defects with concentrations as low as less than a part per million, and it can provide information on the type of defect and its characteristic size. PALS has found application in testing systems as diverse as turbines, polymers, semiconducting devices, biomimetic systems, zeolites, and solar cells. However, PALS mainly suffers of two main limitations: 1) The available positron energy is limited to a few keV, only allowing for surface studies and,2) The positron bunch duration is relatively long, strongly affecting the resolution of the technique. Exploiting recent advances in laser-plasma particle acceleration, it is proposed here to develop a novel laser-driven source of MeV-scale positron beams that will allow, for the first time, volumetric and high-resolution scanning of bulk materials. The short duration of the laser-driven positron beams (~10s of ps) will also allow for a step-change improvement in the resolution of this technique.