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 k(B)T = 0.025 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.