# Recoil Energy

1. ### dranger35

14
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.

2. ### dextercioby

12,327
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.