Temperature Dependence of Positron Annihilation Rates in Noble Gases

The dependence of positron annihilation rates on temperature has been measured for the noble gases. These measurements were carried out using a new technique which, for the first time, makes the positron energy range between kBT0ex0ex=0ex0ex0.025 and 1 eV accessible to experiments. Positrons in a Penning trap are heated to about 1 eV, and then cool to room temperature by collisions while maintaining a Maxwellian velocity distribution. The positron annihilation rate is measured during the cooling. Experimental data are in good agreement with theoretical calculations.