Many experiments that are impossible to perform with conventional positron sources (DE ~ 2 eV), are easily accessible using the cold positron source developed in our laboratory (DE ≤ 25 meV). Several experimental programs have been carried out or are now underway to take advantage of this unique positron source.

CROSS SECTION MEASUREMENTS

Inelastic c. s. for two CO2 vibrations

An experimental program is currently underway to systematically measure positron scattering cross sections from a variety of targets. Using the cold positron source we are able to measure differential elastic, total and total inelastic scattering cross sections.We have also made the first measurments of energy resolved cross sections for vibrational excitation, and the first state-specific measurements of electronic excitation of molecules by positron impact. For more on cross section measurements, click here.

ANNIHILATION EXPERIMENTS

The VFR mechanism for e+ binding

An important property of positrons is that they may annihilate with the electrons in atoms and molecules, producing detectable 511keV gammas. In the past, our lab measured the annihilation rates of room temperature (~ 25 meV) positrons in a large variety target gasses. This revealed unexpectedly high annihilation rates in large molecules. We now use our unique energy resolved beam to measure the annihilation rate in targets as a function of incident positron energy. The resonances we observe have been attributed to vibration mediated positron-molecule bound states. More information on annihilation studies can be found here.

Papers about our atomic physics experiments.