What is filtering in industrial radiography?
In this article:
- Filtering in industrial radiography involves placing metal layers (filters) between the radiation source, object, and detector to selectively absorb low-energy (soft) radiation.
- Filters in front of the object “harden” the radiation, improving penetration and reducing excessive contrast in objects with varying thicknesses.
- Filters placed behind the object help absorb scattered radiation, enhancing image contrast and overall radiographic quality.
- Common filtering materials include lead, copper, and steel, chosen based on their absorption characteristics and the energy of the radiation used.
- Filtering is essential for optimizing image clarity, minimizing noise, and ensuring consistent results in non-destructive testing (NDT) applications.
Any material, such as a metal layer between a radiation source and film, causes absorption and filtering. The position of the metal layer plays a crucial role in its effect. A metal layer in front of the subject blocks soft radiation, thereby “hardening” the radiation. The degree of hardening depends on the material type and thickness. This phenomenon is utilized to reduce excessive contrast (density variation) when inspecting objects with significantly different thicknesses. Placing a metal layer between the object and the film shields soft scattered radiation generated within the object, improving contrast and consequently enhancing image quality. This shielding method is applied, for example, when using cobalt-60 in combination with a speed screen sensitive to scattered radiation. Lead, copper, and steel are suitable shielding materials.