## Recoil Energy

What is the recoil energy (in eV) of a 57Co nucleus
emitting a 14.4 keV gamma ray?

If anyone knows the equation that I can use, thanks.

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 Blog Entries: 9 Recognitions: Homework Help Science Advisor Since the energy of the photon is small (i think it's not $\gamma$,are u sure it's not MeV...?),you can use the nonrelativistic formula for KE... For a nice use of the total momentum conservation law ,assume the nucleus to be initially at rest. Daniel.