Lifetimes of Resonance Lines of Cadmium

The mean lifetime of the triplet resonance line $5^1{S}_0-5^3{P}_1$, 3261A, of cadmium was measured by the alternating voltage method. The value found was 2.14×${10}^{-6\mathrm{}}$ second, with an estimated precision of three percent. Similar measurements made to determine the mean lifetime of the singlet resonance line, $5^1{S}_0-5^1{P}_1$, 2288A, showed that the excitation which resulted in the emission of this line was mainly due to cascading from a higher level (or levels) by infra-red transitions, the excitation to the $5^1{P}_1$ level by electron impact being relatively much less probable than that to the higher level. The lifetime of the infra-red transition was found to be 9.0×${10}^{-9\mathrm{}}$ second. From the form of the curve showing the dependence of the persistence of the radiation emitted by the excitation tube upon the vapor concentration, the mean lifetime of the 2288A transition was estimated as approximately 2.1×${10}^{-9\mathrm{}}$ second. The lifetime of the subordinate series lines 5086-4800-4678A was found to be ${10}^{-7\mathrm{}}$ second, but since the measurements were affected by absorption and re-emission of the radiation, this value can be taken only as the maximum possible value of this lifetime. For the diffuse subordinate series lines, $5^{3}P-5^{3}D$, similar measurements showed that their lifetime was not greater than ${10}^{-7\mathrm{}}$ second.