Circular dichroism e ects in atomic x

It is shown that a speciic beyond-dipole-approximation polarization eeect in elastic photon-atom scattering, resulting in circular dichroism (CD) when the scattered photon has a suitable observed linear polarization, has signiicance in the x-ray regime. Ground state atoms are considered, assumed to be randomly oriented. The cross section, given our assumptions, is written in terms of photon Stokes parameters and four real photon-polarization-independent atomic parameters (which depend on the vectors of the problem and the two invariant scattering amplitudes). Numerical results are given for the case of scattering from ground-state atoms with Z=29, Z=54 and Z=92. Attention is given to determining the regime where the dichroism eeect may be experimentally observable. It is seen to be largest for intermediate angles, high Z and high (hundreds of keV) photon energies, increasing to an approximately 20% eeect in cross sections. The parameter determining this eeect is also responsible for the appearance of elliptically polarized scattered photons for 1 the case of a suitable linearly polarized incident beam.