Increasing the accuracy of cold Fe opacity measurements to help resolve the solar Fe opacity puzzle

Iron opacity at electron densities and temperatures similar to solar interior conditions was obtained using the Z machine at Sandia National Laboratories. It was found to be 30-400% higher than what is used in standard solar models. In contrast, it is expected that opacity near solar conditions should be lower than the mass attenuation coefficients of x-ray radiation at room temperature (cold opacity). The caveat is that experimental values for opacity at room temperature are reported to within 10% error at best. The present project attempts to reduce these errors. Cold opacity is determined here using transmission measurements of an iron foil at three different characteristic line energies in the soft x-ray 6-13 Å range. Initial transmission measurements have shown that a few percent error on transmission can be achieved. The required areal density is independently measured by two methods: Rutherford Backscattering Spectroscopy using an ion beamline and an AutoEdge technique using 3-17 keV x-ray transmission over a continuous photon energy range. 

Sandia National Laboratories is a multimission laboratory managed and operated by NTESS LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. DOE’s NNSA under contract DE-NA0003525.