Direction of Photo Electron Emission I was looking for information on how the photo electrons are emitted when under X-ray radiation. In this ancient review paper here http://authors.library.caltech.edu/1551/1/WATpr28.pdf they state that the most common angles for non polarized X-ray beams (of various energies) range roughly at around 70-80 degrees with the beam. It is unclear to me, whether the photo electrons are moving towards the source of the X-ray beam or away from it ? Undergrad texts do not seem to shed light on this matter, the best one gets is pictures with emitted electrons being at a 90 degree angle to the incoming photon. Also, I assume this angle is given for a cone, i.e. it's 70-80 w.r.t. the beam, but with 2pi angle around the beam ?
 A: Referring to the Watson 1928 paper you cited (see footnote 31 on page 737) I infer the following.
The most probable direction of initial photo-electron ejection is a little forward of perpendicular to the incoming un-polarized X-ray beam (based on ejection being parallel to the electric vector of the x-ray photons which vector is perpendicular to the beam length).  
So for un-polarized x-rays the electron vectors will form a cone opening up "down-beam" away from the x-ray source.  The half-angle of the cone is beta but beta is very close to 90 degrees.  The authors hypothesize that the emitted photo-electrons are prone to scattering by atoms surrounding the photo-electron source atom.  They say it is this scattering which accounts for the observed distributions being other than a spike at angle beta.  They say that application of a geometrical scattering model like Rutherford nuclear scattering appears to account very well for the scattering patterns reported from the cited experiments.
In the fu-berlin paper cited by Carl Witthoft, which describes X-ray Photoelectron Spectroscopy XPS, it is written " XPS in condensed matter one must
note that the method is very surface sensitive, because only photo electrons from a
thin surface layer are emitted lossless. "
In http://journals.aps.org/pr/abstract/10.1103/PhysRev.23.137 the abstract of a 1923 paper by Bubb.F. there is a rough description of photoelectron emission angles of photo-electrons from a block of parafin wax produced by polarized beam of x-rays.  (Sadly I can't access the body of this paper).
Of course all this is many years old so I am sure that there must be some more up-to-date descriptions somewhere.  The wikipedia article for XPS (http://en.wikipedia.org/wiki/X-ray_photoelectron_spectroscopy) doesn't appear to mention scattering angle although the overview diagram indicates "take-off angle".
