If said gamma rays strike atoms of the same element in a similar structure, another gamma ray of the same frequency may be emitted, however that emission is always recoil free.  
It enables exact measurements of relative motion made in space docking, as well as in measurements of magnetic, gravitational and electric fields.  It describes those radioactive substances where atoms are held in a tight crystalline structure, and gamma rays are emitted at a frequency corresponding to the difference between nuclear ground-state energy and excited-state energy.  If said gamma rays strike atoms of the same element in a similar structure, another gamma ray of the same frequency may be emitted, however that emission is always recoil free.  FTP, name this effect named for the winner of the 1961 Physics Nobel.
It enables exact measurements of relative motion made in space docking, as well as in measurements of magnetic, gravitational and electric fields.  
Mossbauer Effect