Why are long wavelengths considered harmful in an x-ray beam?

Long wavelengths in an x-ray beam are considered harmful primarily because they can increase tissue dose. The reason for this is that longer wavelengths correspond to lower energy photons. Lower-energy x-rays are less capable of penetrating through tissues and therefore are more likely to be absorbed rather than passing through the body.

When these low-energy photons are absorbed by tissues, they can contribute to an increase in the radiation dose that the tissue receives, which could lead to a higher risk of radiation-induced effects. In medical imaging, specifically, utilizing x-rays with inappropriate wavelengths can lead to unnecessary exposure and potentially compromise patient safety.

In contrast, shorter wavelengths with higher energy are more effective at penetrating tissues, which results in better image quality and reduced unnecessary dose to the surrounding tissues. Thus, while the other options might point to different aspects of x-ray performance, the critical point about long wavelengths is their tendency to increase the tissue dose due to higher absorption rates.