Magnetic Dichroism in the Angular Distribution of Atomic Oxygen 2p Photoelectrons

A substantial difference in the angular distributions of 2p photoelectrons from polarized oxygen atoms was found for two antiparallel atomic polarizations. This magnetic dichroism was studied as a function of photon energy from 25 to 52 eV. Our method extends traditional photoelectron angular distribution measurements of open shell atoms to “complete” experiments in similar to spin-resolved measurements. The observed dichroism allows a determination of the dipole matrix elements for the εs and εd photoelectrons and their phase difference including the sign

Compton double-to-single ionization ratio of helium at 57 keV

We have measured the Compton double-to-single ionization ratio of helium using an ion time-of-flight spectrometer along with monochromatized synchrotron radiation of 57 keV. This photon energy is high and probes the Compton ionization alone, since the photoionization makes only a negligible contribution to the total cross section. Comparing our result, which is (1.25±0.3)%, with theoretical calculations and measurements at lower energies shows that this energy is most likely still not high enough to confirm the value of the asymptotic high-energy limit experimentally