Model of K-edge absorption in a hot, dense plasma

A theoretical model for the calculation of the shape and position of the K-shell absorption edge in a hot, dense plasma is described. In the model, degeneracy and continuum lowering contributions due to free electrons are treated as perturbations on the continuum and the bound state. The effect of fluctuations is taken into account by the use of the first neighbor distribution function which is used to form the weighted average of the spectrum due to the first shell of ions surrounding the central ion. The model is used to predict the shape of the aluminum K-absorption edge over a range of compression ratios from 1 to 8 and temperatures from 1 to 25 eV. It is found that, at modest temperatures and densities, the shift is compression dependent rather than temperature dependent, whereas the width of the K edge is temperature dependent rather than compression dependent. Under more extreme conditions both the shift and the width become dependent on both the temperature and the density. The results for the shift from our model are compared with other theoretical models.