Half-Life of the Long-LivedTc99

The half-life of ${\mathrm{Tc}}^{99}$ has been determined on materials isolated both from fission products and from irradiated molybdenum. The determinations were made on aliquots of solutions prepared by dissolving weighed portions of compounds of known composition. The counts were made absolute by comparing them with ${\mathrm{Co}}^{60}$ and RaDEF standards. These determinations resulted in a value of 2.12×${10}^5$ years for the half-life of ${\mathrm{Tc}}^{99}$. A detailed description of the absolute beta-counting techniques is given.