Radiation burn-through measurements to infer opacity at conditions close to the solar radiative zone-convective zone boundary

Recent measurements at the Sandia National Laboratory of the x-ray transmission of iron plasma much higher than predicted by theory have cast doubt on modelling of iron x-ray radiative opacity at conditions close to the solar convective zone-radiative zone boundary. An increased radiative opacity of the solar mixture, in particular iron, is a possible explanation for the disagreement in the position of the solar convection zone-radiative zone boundary as measured by helioseismology and predicted by modelling using the currently accepted elemental composition based on photosphere analysis. Here we present data from radiation burn-through experiments which do not support a large increase in the opacity of iron at conditions close to the base of the solar convection zone and provide a constraint on the possible values of both the mean opacity and the opacity in the x-ray range of the Sandia experiments. (author)