Terms

Question 1

Explain Photoelectric Effect

Answer 1

The process in which a photon of energy transfers its total energy to an electron In some shell of an atom.

This energy may be only sufficient to move the electron from one shell to another, or it may be sufficient to remove the electron completely from (to ionize) the atom.

Question 2

Explain Compton Scattering

Answer 2

Not True absorption, since part of the photon’s energy is not absorbed but merely redirected.
In Compton effect a photon collides with an electron. The photon only shares its energy with struck electron.
The electron that was struck is normally knocked out of orbit and constitutes a “free” electron.

Question 3

Explain Incoherent Scattering

Answer 3

The energy of the scattered photon is always less than the primary photon.

Question 4

Explain Coherent Scattering / Rayleigh

Answer 4

If the photon does not experience an energy shift upon being scattered by an atom.
It can only occur for soft radiation for which the binding energy of the electrons in their atomic shells is important.

Question 5

Explain Pair Production

Answer 5

Very high energy photons are absorbed in matter by a process in which a photon is converted in the electrical field of a nucleus into an electron and a positron.

Question 6

What is Under Cut Scatter ?

Answer 6

Primary radiation striking the film holder or cassette through a thin portion of the specimen will cause scattering into the shadows of the adjacent thicker portions.

Question 7

What is Backscatter Radiation?

Answer 7

Any other material, such as a wall or floor, on the film side of the specimen may also scatter an appreciable quantity of x-rays back to the film.

Question 8

What is Side Scatter?

Answer 8

caused by the wall or any other object close to the side of the specimen.

Question 9

What is Internal Scatter?

Answer 9

As radiation passes through a specimen a type of scatter is created that cannot be reduced in any way.

Question 10

Lead Foil in direct contact with the film has which 3 principle effects?

Answer 10

1) it increases the photographic action on the film,

2) it adsorbs the longer wavelength scattered radiation more than the primary

3) it intensifies the primary radiation more than the scattered radiation

Question 11

3 advantages to Lead Oxide Screens

Answer 11

1) Convenience
2) Cleanliness
3) Flexibility

Question 12

What is Screen Mottle?

Answer 12

Closely resembles graininess but is of a softer outline and larger scale.
Associated with purely statistical variation in the number of absorbed x-ray photons from one tiny area of the screen to another.

Question 13

What is Radiographic Contrast?

Answer 13

The density differences from one area to another constitute radiographic contrast.

Question 14

What is Subject Contrast?

Answer 14

Is the ratio of intensities transmitted by two selected portions of the specimen.
Depends on:
1) nature of the specimen
2) the energy (hardness) of the radiation used.
3) the intensity and distribution of the scattered radiation.

Question 15

What is Film Contrast?

Answer 15

Film contrast refers to the slope (steepness) of the characteristic curve of the film.
Depends on:
1) the type of film
2) the processing it receives
3) the density of the film
4) whether or not lead or fluorescent screens are used.

Question 16

Explain “Latitude”

Answer 16

The thickness range that corresponds to the range of useful densities. Latitude depends on the film gradient (contrast) and on the attenuation of the material

Question 17

Explain “Definition”

Answer 17

Definition refers to the sharpness of the outline of the image
Depends on:
1) type of screens
2) type of film (Halation)
3) the radiation energy
4) the geometry of the radiograph (U.G)
5) movement of the part

Question 18

Explain “Graininess”

Answer 18

Clumping of minute silver grains to produce a visual impression.
All film exhibits graininess to the greater or lesser degree.
Graininess of all film increases as the penetrating radiation increases.
If the development time is increased for the purpose of increasing film speed, the graininess of the resulting Image is likewise increased.

Question 19

Radiographic Sensitivity

Answer 19

Is a general term referring to the size of the smallest detail that can be seen on the radiograph.
Also can be defined as the ease with which the images of small details can be detected.
Depends on:
1) Radiographic contrast
2) Definition

Question 20

Way to Reduce Scatter

Answer 20

1) Masking (around the part) on the film
2) Lead backing sheets (under the film)
3) Remove unnecessary objects
4) Lead intensifying screens
5) Copper filter (X-Ray)
6) lead diaphragm (X-Ray)

Question 21

Balance point of lead screens

Answer 21

Steel: .25’’ or more use min 120Kv
Steel: 1.25” or more use min 200kv
Aluminum: 6” or more use min 160kv

Question 22

Lead Foil screens are made from:

Answer 22

94% Lead
6% Antimony

Question 23

Fluorescent screens are made of

Answer 23

Calcium Tungstate (top half)
Lead coated with Calcium Tungstate (bottom)
Advantage: Fast exposure
Disadvantage: Poor Definition