Scatter (3)

Question 1

Materials that are considered to be ___ in relation to radiation energy being used are subject to the greatest amount of scatter

Answer 1

thick

Question 2

More scatter =

Answer 2

greater amount of radiation beams that strike the film in a negative way

Question 3

Internal or undercut scatter

Answer 3

secondary radiation produced by the object under test.

• just inside the edges or borders of the image
• due to part geometry

Question 4

Back scatter

Answer 4

Secondary radiation produced by materials behind the specimen

Question 5

Side scatter

Answer 5

Primary radiation scatted by walls or other objects located next to the specimen

Question 6

Forward scatter

Answer 6

Produced by primary radiation beam before it reaches the specimen but travels in the same direction as the primary beam

Question 7

Methods of scatter reduction

Answer 7

• lead screens
• masking
• blocking
• filters, cones, collimators
• increasing radiation energy (shorten wavelength)

Question 8

Lead screens

Answer 8

reduce long wavelength radiation and intensify primary radiation, reducing exposure time and amount of scatter

Question 9

Masking

Answer 9

Lead can be used around the specimen

- effective means of controlling undercut scatter

Question 10

Blocking materials

Answer 10

Surrounding, filling or immersing the specimen in a high density absorbing material such as; metallic liquids, shot, putties can reduce scatter

thicker specimens produce more scatter
- blocking material should be similar to test specimen material

Question 11

Filters

Answer 11

Thin sheets of varying atomic number and absorption characteristics placed between radiation source and specimen/film, absorbing longer waves

• copper, brass, lead
• hardening radiation = lower level contrast

Question 12

Cones, Collimators, Diaphragms

Answer 12

Restricting the radiation beam

- more homogenous beam and enhance image quality

Question 13

Controlling scatter can:

Answer 13

• improve definition
• improve definition in areas of specimen thickness changes
• improve defect visibility
• improve sensitivity levels (IQI)

Question 14

Increase object to detector distance

Answer 14

farther the object is the greater reduction in scatter reaching film
- consider film distance, source to film and focal spot size

Question 15

Grid Diaphragm

Answer 15

Potter-Buckey Diaphragm

• strips of lead held together by intervening low atomic # strips (beryllium) in a grid shape, absorb stray rays prior to reaching film.
• moves back and forth, strips show up blurred on final image