What defines a monochromatic x-ray beam?

A monochromatic x-ray beam is defined as one that consists of a single wavelength. This means that all the photons in the beam have the same energy, leading to a very precise and uniform interaction with matter, which is crucial in applications like radiographic testing. This uniformity allows for improved resolution and better contrast in the resulting images.

In radiographic applications, such a beam is beneficial because it reduces the scattering effects that occur when multiple wavelengths are present, thereby enhancing the clarity of the image. Monochromatic beams are often generated using special filters or monochromators that selectively allow only a specific wavelength to pass through.

The other choices deal with variations in the beam. A beam with multiple wavelengths would lead to a range of interactions with the material, causing less precision in imaging. A beam generated from multiple sources may introduce inconsistencies in energy levels, further complicating image quality. Finally, a beam filtered through material can alter its characteristics but does not necessarily result in a monochromatic beam unless specific wavelengths are selectively transmitted.