A helium-4 nucleus (rest mass 4.00151 u) is formed when a helium-3 nucleus (rest mass 3.01493 u), stationary in the laboratory frame, captures a slow neutron (rest mass 1.00867 u), in the following reaction.
Determine the energy (in MeV) of the γ-ray in the laboratory frame. (1 u ≡ 1.66 × 10−27 kg.)
The Attempt at a Solution
As far as I can see classically this would be a doddle. With Conservation of Energy and momentum to be taken into consideration before and after. However without the initial velocities of the neutron or the recoil velocity of the He-4 Nucleus I am not sure how to calculate the energy of the gamma ray. I'm also pretty unsure where the relativity comes into this.
The neutron is slow, so not traveling relativistically, the initial nucleus is at rest. The gamme ray will travel at c, which makes it a pain all in all that i can tell since working out the Lorentz factor is impossible when V=C.
Thanks for any input.