The transition probabilities of twenty-nine lines of Fe I have been determined by combining (1) the measurement of the branching ratio for all the known transitions which depopulate a level with(2) the measurement of its lifetime.
The lifetime was obtained by the beam-foil time-of-flight method. Iron atoms accelerated to an energy of 500 kev were excited by letting them traverse a thin carbon foil. The variation of the light emitted in a particular transition was measured as a function of the downstream distance from the foil to determine the lifetime of the upper level of the transition. The levels studied were restricted to energies higher than 6 ev. to avoid cascading repopulation.
For the branching ratio measurements, the iron levels were excited in a hollow-cathode discharge. Two monochromators were used to measure simultaneously (1) the intensity of each known transition from the level under investigation, and (2) the intensity of a reference line to monitor the population of that level.
The transition probabilities obtained are compared with other recent measurements by different techniques. As far as the limited overlap permits comparison, agreement is found among theseresults.
Comparison with the Corliss and Tech compilation indicates:1. The CT tables are in error by an amount that increases with the excitation energy of the upper level.2. The CT tables yield reliable branching ratio for the strongest lines. However, deviations up to a factor of three may occur for the weakest branches.
The new transition probabilities are used to determine a photospheric solar iron abundance. The result obtained supports the high iron abundance determined by Garz et al. in agreement with the corona values.
