Measurement of the photoionization cross section of neutral iron

Abstract
The photoionization cross section of neutral iron, in thermal equilibrium 2300 K, was measured to be (5.00.7+0.4) × 1018 cm2 at 1540 Å (8.05 eV). At this temperature more than 98% of the atoms are in the levels of the ground term. The iron vapor was produced in a resistively heated furnace, and the column density was determined by the hook method. The optical depth of the iron vapor was measured with a photoelectric detector. The absolute measurement of the cross section can be used to calibrate existing data which cover a wide range of wavelengths.