1. The problem statement, all variables and given/known data b) Calculate the recoil shift for the most energetic lyman line from a free H atom. c) Calculate the recoil shift for the emission of a 14.4keV gamma from a free atom of Fe-57. 2. Relevant equations E = hc / [itex]\lambda[/itex] = h [itex]\nu[/itex] [itex]\Delta[/itex] E = E^2 / 2mc^2 3. The attempt at a solution I'm still not sure I'm going about this correctly... b) start by finding the most energetic lyman line E = hc / [itex]\lambda[/itex] = (1.981E-16)/(912A) = 2.17E-19 (this is where I think my error is). Then find the recoil shift [itex]\Delta[/itex] E = E^2 / 2mc^2 = (4.72E-38)/(0.003) = 1.57E-35. c) calculate the recoil shift directly using the mass for Fe-57 [itex]\Delta[/itex] E = E^2 / 2mc^2 = (207.36)/(1.89E-22)(2.99E8)^2 = 12.27MeV ...again this answer just feels wrong, how can a keV scale emission result in an MeV scale recoil? Quite clearly I've made some horrible mistake in here, I need some help to find what I did wrong.