Which of the following best describes a situation when the photoelectric effect is more likely to occur?

The photoelectric effect occurs when photons are absorbed by a material, causing the ejection of electrons from that material. This phenomenon is more likely to take place when low-energy photons interact with dense materials. Dense materials, such as lead or other heavy metals, have a high atomic number and electron density, which increases the probability of photon interactions that can result in the photoelectric effect.

Low-energy photons can have enough energy to overcome the binding energy of inner-shell electrons in these dense materials. As a result, when these photons strike the material, they can transfer their energy effectively, allowing the electrons to be ejected. This interaction is particularly significant in fields like radiology and radiation therapy, where understanding the interactions of different energies with various tissues is crucial for effective imaging and treatment protocols.

In contrast, high-energy photons, such as those from X-rays or gamma rays, are more likely to engage in Compton scattering rather than the photoelectric effect. Photons traveling through a vacuum do not interact with any material, and interactions with air molecules are generally minimal regarding the photoelectric effect, as air is not dense enough to facilitate significant absorption and electron ejection.