Introduction

The use of a focused beam of high energy (MeV) protons to image and analyse thin samples offers many unique advantages over existing techniques. As shown in Fig. 5.1, the interaction of the proton beam with matter can take many forms. Non-nuclear reaction products such as characteristic X-rays, secondary electrons, backscattered protons and nuclear reaction products such as gamma rays and nuclear particles, can provide a wealth of analytical information on the sample under investigation. If the sample is thin enough to allow the protons to pass through, then the subsequent detection of the transmitted protons allows structural information to be obtained.

Described here is an example of the use of three of the techniques associated with the proton beam interaction, as applied to Alzheimer's Disease tissue. These techniques, utilising the detection of characteristic X-rays, back-scattered protons and transmitted protons, can be simultaneously applied to form a powerful array of nuclear particle based techniques which we have called nuclear microscopy.

Nuclear microscopy: techniques for analysis and features of the scanning proton microprobe

Proton induced X-ray emission (PIXE)

When a particle collides with an atom, the probability of knocking out an inner core electron is optimised when the velocity of the incoming particle matches the velocity of the inner core electron. This occurs at keV energies when electrons are used as the impinging particle, and at MeV energies when protons are used.