I recently came upon the reaction $$ p\ +A\rightarrow p\ +\gamma \ +A\rightarrow p\ +p\ +\bar{p}\ +A$$

That is, an energetic proton interacts with a nucleus, produces a photon (while the nucleus remains unchanged), and the photon then produces a pair of proton and antiproton. Given that the energy of the original proton is enough, this should be able to happen.

Is the nucleus $A$ necessary for the interaction? Wouldn't it be able to (spontaneously) happen in its absence as well, if the proton had kinetic energy at least equal to $2m_p$?