Mossbauer Effect/Spectroscopy

[mississippichem]

I'm a chemist with an interest in Mossbauer spectroscopy. I was wondering if any of you physics guys can help me understand the origin of the Mossbauer effect. I've had difficulty finding good resources on this topic. I understand it involves atoms heavier than K absorbing gamma photons which in turn causes them to emit a whole number of phonons...

 

I don't understand:

 

• What makes some Mossbauer events happen without recoil energy loss?
   
  
• Is there a nuclear spin requirement for a nuclei to be Mossbauer active as is the case with NMR active nuclei?
   
  
• Why are no nuclei lighter than potassium Mossbauer active?
  

This isn't homework, just curious.

[swansont]

AFAIK the recoil vanishes because the atom is in a lattice and is not free to recoil, i.e. the effective mass is large, so the momentum is shared by a very large number of atoms. In addition, the vibrational modes are quantized, so that if there is energy loss due to recoil, it will be due to the creation of phonons, and give a quantized shift in the energy.

[mississippichem]

Thankyou, that answers my first question. I wonder if any electron excitation effects (fluorescence, compton, rayleigh) happen from absorption in the gamma region. Im not familiar with what happens from absorption of such high magnitude. Is gamma radiation so ionizing that these phenomena don't occur as they do with absorption of UV, vis, Infared?