Hi guys, I've been struggling with this problem for a while now and cant seem to get anywhere with it. Roughly speaking: We are given that an Ar37 atom decays through electron K capture into a Cl37 atom and a neutrino, plus a gamma ray of wavelength 4.2 Angstroms. The binding energy of the K capture is 3KeV and the mass difference between Ar37 and Cl37 is 816KeV. We've been asked to calculate the recoil energy of the Cl37 atom when the neutrino is emitted. We know the answer is 9.6eV but cant seem to get anywhere near it! So far I've calculated the Q value to be 813KeV through the mass difference minus the binding energy of the captured electron. I've tried using linear momentum conservation knowing that the energy of the neutrino is E = pc. However, I cant even see how to begin. Can anyone offer any starters? I've tried searching everywhere :( Thanks. I believe these are all the values we need to calculate it, but i am at a loss on what to do!