A stationary nucleus of samarium-157 (
) emits a gamma-ray (γ-ray) photon of energy 
. Determine, for one 
-ray photon:
its wavelength
its momentum.
Using your answer to (b)(ii), determine the speed of the samarium-157 nucleus after emission of the photon.
By reference to your answer in (c)(i), explain quantitatively why the speed of the samarium-157 nucleus may be assumed to be negligible compared with the speed of the photon.
.
.
.
which is the speed of the photon.
