Final answer:
The most probable interaction in lead for thallium and technetium photons is the photoelectric effect, which predominates at low to moderate energies and with high atomic number materials, while Compton scattering would be more likely at higher energies.
Step-by-step explanation:
The interaction that is most probable in lead for thallium and technetium photons is the photoelectric effect. Lead, having a high atomic number, is particularly effective at absorbing photons through the photoelectric effect, which predominates at low to moderate photon energies and when interaction with high atomic number materials.
Compton scattering becomes more significant as the x-ray energy increases and is defined by the interaction between a photon and an electron, where the photon transfers part of its energy and momentum to the electron.
Pair production, another possible interaction, typically becomes significant only for photons with energies above 1.02 MeV. It occurs when the photon's energy is converted into an electron-positron pair within the electromagnetic field of a nucleus.
Rayleigh scattering is mostly relevant for photons with lower energies and involves the elastic scattering of light by atoms and molecules, without a transfer of energy to the scattering medium. Given the energies of thallium and technetium photons, the photoelectric effect is the most probable interaction in lead.