Relativistic, retardation, and multipole effects in photoionization cross sections: Z, n, and l dependence

Electronic stopping power of diamond for electrons and positrons

We assess a new data set of mass electronic stopping powers of diamond for electrons and positrons. To this end, an optical energy-loss function (OELF) for this material is generated from available experimental dielectric properties of the valence band and photoabsorption mass attenuation coefficients, supplemented with a Drude-type analytical expression to interpolate at intermediate energies. From this synthetic OELF, a mean excitation energy equal to (88.5 ± 2.0) eV is extracted and the density-effect correction is evaluated using Fano's simplified method. These quantities then allow calculating the mass electronic stopping power of diamond for electrons and positrons by means of the relativistic Bethe formula. The present results for 1 keV-1 GeV electrons in diamond are 0.9%-3.3% smaller than those corresponding to graphite as tabulated in ICRU Report 90.

Contribution of the E2 transitions to the opacity of hot and dense plasmas of heavy elements by an average-atom approach

The contribution of electric quadrupole (E2) transitions to the opacity of hot and dense plasmas is taken into account by using an average-atom model. As an example, the increase of the opacity of Au due to the E2 transition is shown to range from less than 1% to more than 10% depending on density and temperature. It reaches 15% when the density and temperature are, respectively, 100 g/cm(3) and 5000 eV. The most significant influence comes from the E2 photoionization processes.