In the photoelectric effect, what happens to the X-ray?

• A. It is completely absorbed
• B. It is partially absorbed
• C. It is reflected
• D. It is transmitted

Answer: (A)

In the context of the photoelectric effect, the correct understanding is that the X-ray is completely absorbed. This phenomenon occurs when an incident X-ray photon interacts with an inner shell electron of an atom. The energy of the X-ray photon must be greater than or equal to the binding energy of the electron for the interaction to take place.

When this absorption occurs, the X-ray photon transfers all of its energy to the electron, allowing it to overcome its binding energy and be ejected from the atom. This results in the complete absorption of the X-ray photon, leading to the emission of a photoelectron. The effect is most pronounced in materials with high atomic numbers, where the likelihood of interaction is greater due to higher electron binding energies and denser atomic structures.

Understanding this process is crucial in bone densitometry and medical imaging, as it helps to explain how X-rays can provide information about bone density and structure, highlighting the role of attenuation of X-ray beams in different types of tissues.