The Use of Positron Emission Particle Tracking (PEPT) to Study the Movement of Inclusions in Low-Melting-Point Alloy Castings

Positron emission particle tracking (PEPT) employs a radioactive particle that decays by emission of positrons. These positrons collide with local electrons to produce gamma-rays emitted at 180 deg to each other; detection of these gamma-ray pairs allows the location of the radioactive particle to be identified within a few millimeters. This technique has been tested to determine its applicability to the study of inclusions in cast metals. To use particles representative of inclusion sizes in castings, both alumina particles and particles of an ion exchange resin were employed. These were within a size range of approximately 60 to 100 mu m, made radioactive by adsorption and ion exchange techniques, respectively. The radioactive particles, of activity 100 to 1000 mu Ci, were introduced into tube-shaped castings made from the low-melting-point alloys Field's metal and Lensalloy-136, cast into an acrylic mold. The technique allowed the particle track to be determined from the point of initial introduction to the final resting place of the particle, with increasing reproducibility being obtained as the reproducibility as the casting technique was improved. Experiments in which filters were placed in to the running system showed that the removal of the particles by the filters varied according to the filter pore size.