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

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.