What device is used to remove long-wavelength x-rays from the primary beam?

The device used to remove long-wavelength x-rays from the primary beam is a filter. Filters are specifically designed to absorb lower-energy x-rays that may not contribute meaningful diagnostic information and could increase patient exposure to unnecessary radiation. By using a filter, only the higher-energy x-rays that are more effective for imaging are allowed to pass through to the patient and the detector. This enhances image quality and minimizes radiation dose, making the procedure safer for patients while retaining the necessary diagnostic capabilities.

In contrast, a collimator primarily shapes the x-ray beam and limits its size to focus on a specific area of interest, while a shield protects against unwanted radiation exposure. A detector is responsible for capturing the x-ray image but does not actively modify or filter the beam. Hence, the filter is the appropriate choice for removing long-wavelength x-rays from the primary beam.