Lifetimes of electrons in the 3 P-and 4D-levels of sodium are measured. The sodiumatoms are excited by short pulses of electrons with energies between 2 and 8 eV. The time dependence of the emitted light is determined by direct oscillographing via photomultiplier as well as by counting single quantas. The counting technique corresponds to the delayed coincidence method and employs a sampling oscilloscope. Lifetimes of the 3P-and 4D-levels were found to be 14.0 and 52.1 nsec respectively. From these values the absorption oscillator strengths 1.11 and 0.095 were calculated for the 3S--3P-and 3P--4D-transitions.
A. EinleitungDas Prinzip der verwendeten Apparatur zur Bestimmung der Lebensdauer wird an Hand der Fig. 1
Abstract. Ionization cross sections for electron impact are measured with crossed beams of Mg atoms and pulsed electrons. Total numbers of particles are determined by the light emission of excited atoms. The ionization cross section obtained for electron energies from 7 eV to 60 eV has its maximum value qz(max)= 7.8 9 10-~ cm 2 at 12 eV electron energy.
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