With rare-earth intensifying screens, X-ray films are sensitive to which light spectrum?

The correct choice is based on the specific characteristics of rare-earth intensifying screens and their interaction with X-ray films. Rare-earth materials, such as lanthanum and gadolinium, emit light primarily in the blue-green spectrum when they are excited by X-ray radiation. This emitted blue-green light enhances the exposure of the film, making it more sensitive and allowing for reduced radiation dose during the imaging process.

X-ray films designed to work with these screens are formulated to have a high sensitivity to this specific spectrum of light, enabling optimal image quality with minimal dose. The use of blue-green light supports better photographic quality and shortens film exposure times, which is particularly beneficial in medical radiography.

While other light spectra, such as blue, red, and yellow, may be associated with different types of films or intensifying screens, they are not the primary wavelengths that rare-earth screens are designed to work with. Hence, these alternatives would not be appropriate for X-ray films using rare-earth systems.