A method of measuring positron lifetime is used to investigate temperature dependence of positron trapping at defects in neutron-irradiated silicon crystals. The lifetime spectra can be separated into two components. The long lifetime component

attributed to negatively charged divacancies

is found to be a constant value of 325±9 ps in the temperature range of 109-300K.The positron trapping displays a negative temperature dependence and the behavior can be described in terms of a cascade model of positron trapping. In the low temperature region the positron trapping cross section varies with temperature as T-1.7