Filtration of X ray Beam

# What is the function of the filtration process while taking radiographs?
A. Remove the short wavelength photons
B. Remove the portion of long wavelength photons
C. To increase the radiation dose to the patient
D. To increase the scatter of secondary radiation

The correct answer is: B. 

X-ray photons with short-wavelength have high penetration energy and are useful for diagnostic radiology X-ray photons of long-wavelength have low penetration energy and contribute to patient exposure only. These photons are removed by keeping aluminum filters in their path. The half-value layer is about 1.5 mm for an X-ray tube of 70 kVp and is about 2.5 mm for higher voltages.