What is the minimum energy a photon must have to create an electron-positron pair near a nucleus?

The correct choice highlights the energy threshold required for photon interactions that result in the creation of an electron-positron pair. According to the principles of pair production in particle physics, the minimum energy needed to create such a pair is determined by the rest mass energy of the produced particles.

An electron and a positron each have a rest mass energy of approximately 0.511 MeV. Therefore, the combined energy required for both particles is 0.511 MeV + 0.511 MeV, which totals 1.022 MeV. However, it is essential to account for the binding energy and interactions with the nucleus during the pair production process. The energy of the photon must exceed this total to ensure that the pair can be created and to account for additional energy that might be absorbed or lost during the interaction.

As a result, the minimum energy for a photon to create an electron-positron pair near a nucleus must be at least 1.02 MeV, which is why this choice is correct. This understanding is fundamental in the field of medical dosimetry and particle physics, illustrating the energy dynamics involved in such particle interactions.