Positron scattering & annihilation using a hot cell
To date, energy resolved annihilation and scattering measurements have been made only on atoms or molecules with appreciable vapor pressures at room temperature. We are developing an experiment that will incorporate a hot cell into the current apparatus. It will allow us to perform annihilation experiments on molecules and atoms (e.g., polycyclic aromatics (PAHs) and other larger molecules) that have low vapor pressures at room temperature. Of particular interest is C60, the "buckyball." Because of its unique cage structure, this molecule is predicted to have interesting particle-in-cage resonances with both electrons and positrons. These states may be detected via either scattering or annihilation. Molecules like PAHs are interesting because they naturally occur in diesel soot, mothballs and in the interstellar medium. Our unique positron probe may shed some light on their electronic and surface-chemical structure. More generally, experiments with large molecules will allow us to further explore positronically-excited bound states, which were first observed in large alkanes.
High resolution positron scattering & annihilation
By refrigerating the electrodes of our high field trap, we can reduce the temperature of stored electrons or positrons through cyclotron cooling. In conjunction with our buffer gas trap, this will allow us to produce a pulsed positron beam with a greatly improved energy resolution (i.e., ~1 meV instead of ~25 meV). In our annihilation experiments, this improved resolution will allow us to better distinguish various resonant features. In particular, we may be able to determine the natural widths and selection rules for the observed vibrational Feshbach resonances.
Multicell trap for storing large numbers of positrons
Our lab continues to pursue more advanced techniques for positron storage and manipulation. The multicell trap will allow us to store unprecedented numbers of positrons by using rotating wall compression, cyclotron cooling, and other plasma techniques to stack high densities of positrons into many identical traps or "cells." In the future, a portable version of this trap could be used as a safe, refillable positron source for research laboratories and medical facilities. It could also be used to produce high intensity positron pulses for condensed matter experiments and diagnostics.