What happens to TLD crystals as exposure increases?

Thermoluminescent dosimetry (TLD) crystals are designed to measure ionizing radiation exposure. When TLD crystals are exposed to radiation, they absorb energy in the form of ionizations. As the exposure to radiation increases, the amount of energy stored in the TLD crystals also increases.

When these crystals are subsequently heated, they release the absorbed energy in the form of light, which can be measured to determine the amount of radiation exposure. Therefore, as exposure increases, the intensity of light emitted by the TLD crystals during readout becomes greater, which correlates with higher levels of radiation dose. This property makes TLDs effective for personal dosimetry and radiation monitoring.

In contrast, options referring to changes such as density or coloration do not accurately reflect the primary response of TLD crystals to radiation exposure, nor do they relate directly to their function in measuring radiation doses. The notion of losing sensitivity also does not apply here, as the crystals retain their ability to respond to higher exposures, thus providing accurate readings for the amount of radiation they have encountered.