7: Exposure Techniques

Question 1

Position of what is most critical?

Answer 1

Source compared to specimen and film

Question 2

Using screens in energy levels between ____ and ____ can reduce exposure from 1/3 to 1/2 then they would without.

Answer 2

150 keV and 2 MeV

Question 3

What type of materials are particularly susceptible to scatter?

Answer 3

Denser metals

Question 4

Describe Category 1 materials:

Answer 4

Parts of uniform thickness that have good contact with film, such as flat butt welds or flat plates

(Scatter mainly absorbed - measures don’t need to be taken)

Question 5

Describe Category 2 materials:

Answer 5

May produce scatter at the edges but this subtle loss of sensitivity would be acceptable

Ex. Parts with large radius, tapered parts, chamfered parts and flat but slightly irregular castings

Question 6

Describe Category 3 materials:

Answer 6

Can exhibit undercut scatter from one section of image to other, reducing image quality/clarity

Ex. Parts with complex geometry and heavy section thickness

often require masking/blocking/filters

Question 7

What are the 3 main factors that govern exposure?

Answer 7

1. mA for X-rays OR source for gamma
2. Time
3. Source-to-film distance

Question 8

As a general rule, the mA required for a given exposure is directly proportional to the ___________

Answer 8

Square of focal film distance

M1/M2 = D^2,1/D^2,2

Question 9

If the mA can’t be changed, what should you do?

Answer 9

Adjust exposure or time

T1/T2 = D^2,1/D^2,2

Question 10

mA required for a given exposure is inversely proportional to what?

Answer 10

Time

Question 11

What is referred to as the reciprocity law?

Answer 11

M1T1 = M2T2 = M3T3 = constant

Relationship between mA and time

Question 12

When does the reciprocity law not apply?

Answer 12

When fluorescent screens are used

Question 13

Ideally, direction of beam should be where compared to part?

Answer 13

Perpendicular to main axis of part

Question 14

Medium tubular sections (20-40 mm) may require how many exposures?

Answer 14

Min. of 2 at 90 degrees to each other, but up to 4 may be necessary

Question 15

Large tubular sections may require how many exposures?

Answer 15

3 exposures at 120 degrees or 4 exposures at 90 degrees

Question 16

Double wall exposures are common for pipe diameters less than what?

Answer 16

90 mm

Question 17

For pipe welds, a source placed perpendicular to weld plane is called what?

Answer 17

Double wall, double viewing

Question 18

How many exposures are generally required for the superimposed method?

Answer 18

Typically 3, 60 degrees or 120 degrees to previous

Question 19

When may it be acceptable for a source to be in contact with outside of pipe?

Answer 19

Diameters greater than 90 mm

This would be a double wall, contact exposure

Question 20

What degrees are elliptical exposures offset by? And how many exposures?

Answer 20

Typically offset by 15-30 degrees, requiring 2 exposures set at 90 degrees

Question 21

The location along a welded seam is usually indicated on a radiograph by means of what?

Answer 21

Lead numbers

Question 22

In order to ensure good contact with the weld or casting being radiographed, what are preferred?

Answer 22

Flexible cassettes

Question 23

Cassettes contains film are held in position for exposure by means of what 3 things?

Answer 23

1. Wooden supports
2. Magnetic strips or springs
3. Tape
   (Whatever works)

Question 24

By using small diameter sources (0.3 mm), very small diameter pipes can be shot using the panoramic technique with the acceptable unsharpness. Although the source strength is low, exposure time is not too long because of what?

Answer 24

The source to film distance is small