What causes flood images to appear spotty when the aluminum cover around a scintillation crystal is breached?

The appearance of flood images being spotty when the aluminum cover around a scintillation crystal is breached is primarily due to hygroscopic degeneration. Scintillation crystals, such as sodium iodide (NaI), are hygroscopic materials, meaning they can absorb moisture from the air. When the aluminum cover is compromised, this absorption can lead to a breakdown of the crystal's structure and diminished performance in detecting radiation.

The presence of moisture can create variations in the crystal's uniformity and efficiency in light production. As a result, inconsistencies in the scintillation process occur, leading to the spotty appearances in the flood images. These variations in light output caused by hydration effects disrupt the even response necessary for producing clear and uniform diagnostic images. Thus, hygroscopic degeneration is the primary factor leading to the compromised quality of images in this situation.