What is the term for a photon-nuclear interaction in which energy is converted into sub-atomic particles?

The term you are looking for refers specifically to a process in which a high-energy photon interacts with a nucleus, resulting in the conversion of that photon’s energy into sub-atomic particles, typically an electron-positron pair. This process is known as pair production.

In pair production, if the energy of the incoming photon exceeds a certain threshold (specifically, the combined rest mass energy of the electron and positron), it enables the transformation of energy into matter, thereby creating these two particles. This occurs near the nucleus of an atom because the nucleus helps conserve momentum in the interaction.

In contrast, the other processes mentioned have different mechanisms and outcomes. The photoelectric effect involves a photon being completely absorbed by an atom, resulting in the ejection of an electron but not the creation of new particles. Compton scattering refers to the collision of a photon with a relatively free electron, where the photon transfers some of its energy to the electron and continues on with reduced energy, without producing additional particles. Rayleigh scattering is an elastic scattering process that occurs without any change in photon energy, primarily involving the scattering of light by particles much smaller than the wavelength of the light.

Thus, pair production is the specific interaction that fits the description of converting energy into sub