Final answer:
When worn under a lead apron, a thermoluminescent dosimeter (TLD) measures the organ dose, detecting radiation that passes through the apron and could potentially affect sensitive internal organs.
Step-by-step explanation:
If the thermoluminescent dosimeter (TLD) is worn under the lead apron, it measures the organ dose. The TLD is designed to measure the amount of ionizing radiation absorbed by the body tissues of the person wearing it. When it is placed under a lead apron during an X-ray procedure, it detects the radiation dose that passes through the lead apron, which primarily consists of scatter radiation that has the potential to reach and affect internal organs. This dose is generally low since the lead apron blocks the majority of the direct radiation beam. However, the measurement is crucial for assessing the potential radiological risks to sensitive organs.