When measuring a thermoluminescence (TL) date to the highest possible accuracy, well calibrated radiation sources are of paramount importance. In this paper we will describe a technique whereby calibration may be accomplished to an accuracy better than ±1per thousand This method is used on an alpha emitting radioisotope only recently available from commercial suppliers. The Cm-244 source has properties making it very desirable in TL dating; namely, a relatively long half-life, high alpha particle energy and minimal energy deposition from radiation other than alpha transitions. Table 1 lists currently available alpha sources and some of their characteristics. In the present study we have determined the total energy deposited per second for a collimated curium source, using a cylindrical ionization chamber (by completely stopping the alpha particles in the chamber and measuring the total charge produced by the source). Knowing the total charge and W (the average energy required to form an ion pair), one can calculate the total energy per second emitted by the source. Additional information about the energy distribution of the emitted alpha particles as a function of angle and distance from the source is necessary when source to sample geometry is initially set or changed to ensure that the sample is uniformly irradiated.