Compound filters

## Step1: Understanding the Concept of Compound Filters
### Compound filters are used in radiography to reduce the amount of scatter radiation that reaches the image receptor. They are made up of two or more materials, each with a different atomic number. The first material absorbs the primary radiation, while the second or third material absorbs the secondary radiation produced by the first material.
## Step2: Identifying the Materials
### The materials used in compound filters are typically Thallium Aluminum (ThAl), Copper (Cu), and Tin (Sn). These materials are chosen based on their ability to absorb radiation at different energy levels. ThAl absorbs low energy radiation, Cu absorbs medium energy radiation, and Sn absorbs high energy radiation.
## Step3: Explaining the Functioning of Compound Filters
### When primary radiation passes through the first material (ThAl), it produces secondary radiation. This secondary radiation, which is characteristic of the first material, is then absorbed by the second or third material (Cu or Sn). This prevents the secondary radiation from reaching the image receptor, thereby reducing image noise and improving image quality.