Somatic effects are those that appear in the person who was irradiated and are not passed on to offspring. The lens of the eye is highly radiosensitive, so exposure can lead to cataracts in the irradiated person—a classic somatic reaction that can be dose-dependent and may have a threshold. In contrast, mutations in germ cells are genetic effects and could be inherited by future offspring, which is why options describing germline changes or birth defects in children are not somatic. Therefore, cataracts in the irradiated lens best illustrate a somatic effect.

Dose determines somatic risk because the amount of energy absorbed by body tissues directly drives the chance and severity of radiation-induced damage. More dose means more cells are harmed, raising the likelihood of deterministic effects (which have thresholds and become more severe with higher dose) and increasing the probability of stochastic effects like cancer. Traits such as hair color, eye color, or hand dominance do not influence how radiation interacts with tissues, so they don’t affect somatic risk.

Gonadal shielding is placing a lead shield over the reproductive organs to reduce radiation dose during radiographic exams. It should be used whenever shielding the gonads can be done without obscuring the area of diagnostic interest, with special emphasis on pediatric and young adult patients who are more radiosensitive. If shielding would cover essential anatomy or lie in the primary beam, it should not be used because it would compromise the exam. Shielding lowers dose to the gonads but does not change image brightness, and it should be applied in conjunction with proper collimation and careful technique. In some cases, shielding may not be necessary if the gonads are outside the field or if modern imaging already minimizes dose.

Thermionic emission describes electrons escaping from a heated metal surface, such as the cathode filament, because the thermal energy provides enough energy to overcome the material’s work function. In radiography tubes, heating the filament makes electrons boil off to form a cloud that is then accelerated toward the anode to generate the X-ray beam. This distinguishes it from other terms: Bremsstrahlung is X‑rays produced by deceleration of electrons in the target, fluorescence is light emitted by a material after energy absorption, and secondary emission is electrons ejected due to incoming electrons hitting a surface, not due to heating. So the statement correctly identifies thermionic emission.