What does the field of radiobiology study?

The field of radiobiology specifically investigates the effects of ionizing radiation on living organisms, which includes the biological responses and mechanisms that occur as a result of exposure. Understanding how living tissues react to ionizing radiation, which can cause cellular damage, mutations, or even death, is crucial for numerous applications, especially in medicine, including radiation therapy and understanding radiation safety.

The other options relate to different aspects of radiation and its effects but do not encompass the primary focus of radiobiology. For instance, the thermal effects of radiation and the interaction of X-rays with various substances are important in understanding radiation physics and safety but do not directly address how living organisms respond biologically to radiation exposure. Similarly, materials used in radiation shielding involve engineering and safety measures to protect against radiation but do not delve into the biological implications of radiation on living tissues. Thus, the correct focus of radiobiology is identified in the chosen answer.