DEVELOPMENT OF A REFLECTION GEOMETRY POSITRON REEMISSION MICROSCOPE

The design, construction, and development of an electrostatic positron beam system for reemitted positron microscopy is described. Positrons from a 1.5 GBq Na-22 source are moderated and a primary 10 mm diameter beam formed. The brightness of the beam is subsequently increased by two further stages of focusing and remoderation. The resultant, smaller diameter beam is then focused and impinges on the sample of interest at an angle of 45 degrees to the surface. The incident positron beam optics and reemitted positron imaging optics, integrated to minimise interference between the two, are in reflection geometry to permit the imaging of thick samples. The reemitted positron ensemble is accelerated, magnified, and focused to form an image at the face of a position sensitive detector; contrast in the image is determined by the variation in the probability of reemission across the surface of the sample. The results of tests on the performance of the beam delivery optics are presented together with proposed improvements and possible applications for the prototype system.