a$)$ A beam of photons with just barely enough individual photon energy to create electron$$positron pairs undergoes Compton scattering from free electrons before any pair production occurs. Can the Compton$-$scattered photons create electron$-$positron pairs?

b$)$ An electron and a positron are moving toward each other and each has speed $0\mathrm{.}500$c in the lab frame. What is the kinetic energy of each particle?

c$)$ What is the wavelength of each photon?

d$)$ How does the wavelength compare to the photon wavelength when the initial kinetic energy of the positron and electron is negligibly small?