A CWI is reviewing a Radiographic Testing (RT) procedure that specifies the use of a lead screen. What is the primary function of a lead screen placed on the film side (back screen) during industrial radiography?
- ATo provide mechanical support for the film
- BTo intensify the primary radiation reaching the film
- CTo filter out low-energy X-rays from the source
- DTo absorb scattered radiation originating from the object
Show answer & explanationAnswer & explanation
Correct answer: D. To absorb scattered radiation originating from the object
A lead screen placed behind the film (back screen) primarily functions to absorb scattered radiation that originates from the object being radiographed and travels towards the film. By absorbing this scatter, it reduces fogging and improves the contrast and overall quality of the radiographic image. Front lead screens intensify the primary radiation, and both provide some mechanical support, but scatter absorption is the key role of the back screen.
Why the other options are wrong
- A. While it provides mechanical support, it's not the primary function of a lead screen in terms of radiographic quality.
- B. This is primarily the function of a lead screen placed on the source side (front screen) for X-rays, by emitting electrons.
- C. Filtering low-energy X-rays is primarily done by filtration at the source, or by the front lead screen for some intensifying effects.
RT Back Lead Screen Function
A lead screen placed behind the radiographic film (film side) primarily absorbs scattered radiation generated within the object, improving image contrast and reducing fogging.
- Reduces scatter, which degrades image quality.
- Leads to higher contrast and better definition.
- Also provides some intensifying action, though less than the front screen.
Memory trick: Front intensifies, back stops scatter, both help the image matter.