Workbook #1

Question 1

What year were X-rays discovered and by who?

Answer 1

Roentgen had discovered X-rays on November 8, 1895

Question 2

Xray properties

Answer 2

1. Penetrate matter
2. Produce a latent image on film or an image receptor
3. Produce fluorescence in certain materials
4. Produce ionization of matter

Question 3

photon

Answer 3

• an X-ray as a particle or bundle of energy
• has no mass or charge
• moves in straight lines at the speed of light.

Question 4

Ionization

Answer 4

• Interactions of X-rays with the electrons within the tube head or the patient
• is the process where electrons are removed from atoms due to collisions with x-ray photons

Question 5

Bremsstrahlung Radiation

Answer 5

-is produced when an electron passed near the nucleus of an atom. The negatively charged (-) electron is deflected by the positively charged (+) nucleus. The energy lost by the deceleration of the electron is emitted in the form of a photon of radiation

Question 6

Characteristic radiation

Answer 6

• results when an electron within an atom is ejected from the inner orbit of the atom by an incoming high-speed electron.
• The radiation is specific to, or characteristic of, the particular atom in which the interaction occurs.
• Characteristic radiation makes up only a small portion of the X-rays produced in a dental X-ray unit

Question 7

Examples of electromagnetic radiation

Answer 7

radio waves, microwaves, cosmic rays, and visible light

Question 8

Relationship of wavelength and frequency

Answer 8

-inverse relationship

High Wavelength low frequency and vice versa

Question 9

What type of rays are more penetrating?

Answer 9

High frequency short wavelengths

Question 10

Volt (V)

Answer 10

is a unit of electrical potential that can be considered a measure of work capacity

Question 11

Xray units range for kVp

Answer 11

70 kVp is a common setting

although it may be as low as 60 kVp or as high as 90 kVp

Question 12

A high kVp setting means

Answer 12

will produce X-rays that are more energetic, have greater penetrating power, and has a greater capacity to pass through matter.

Question 13

15 kV rule

Answer 13

Increasing the kilovoltage by 15 would require decreasing the exposure time by one half to keep the image density (darkness) the same.
-For every 15% increase in kV, the density (or darkness) on the resulting image will double

Question 14

Ampere (A)

Answer 14

unit of electrical current, or the number of electrons flowing in an electrical circuit.

Question 15

Units Ampere are measured in X-rays

Answer 15

milliamperes (mA)

Question 16

Thermionic Emission

Answer 16

• The current in the filament circuit in an X-ray machine is used to head a very thin wire (a filament) made of tungsten, similar to the filament in a light bulb. Heating the filament agitates the tungsten atoms; some of the electrons in these atoms escape from their orbits
• The tungsten electrons that have been boiled off form a cloud around the filament, and it is these “free” electrons that are ultimately responsible for generating X-rays.

-Think of boiling off of tungsten electrons

Question 17

milliamperes

Answer 17

The milliamperage setting in the x-ray unit influences the current flowing through the filament and therefore the number, or quantity, of X-rays that will be produced in the x-ray tube.

Question 18

What are the factors that influence the number of X-rays produced

Answer 18

milliamperage

exposure time

Question 19

Components of dental X-ray tube

Answer 19

Cathode
Focusing Cup
Anode
Filter
Tube head housing
Oil
Collimator

Question 20

Cathode

Answer 20

• negatively charged end of an x-ray tube

- consists of the tungsten filament and a focusing cup

Question 21

Focusing Cup

Answer 21

• has a negative electrostatic charge and is usually made of molybdenum.
• shape of the cup and its negatively charge repel the electrons from the filament and keep them suspended in a “cloud” around the filament.
• When the high voltage circuit is activated, the focusing cup’s charge and shape help direct the electrons toward the anode and prevent from spreading out and missing the target.

Question 22

Anode

Answer 22

• positive end of the x-ray tube
• made of tungsten and copper
• a small block of tungsten is embedded in a large copper stem or sleeve to act as the target for the electrons

Question 23

Why is tungsten used in the anode

Answer 23

Tungsten is used because it has a high atomic number and thus can produce many X-rays
-has a high melting point and a low vapor pressure; it will not melt or vaporize, unless extremely long exposures are made or unless many exposures are made in a short period of time.

Question 24

Why is copper used in the anode

Answer 24

Copper is used around the tungsten target to conduct heat rapidly away from the target, thus reducing the wear by heat on the target.

Question 25

Filter

Answer 25

• aluminum filter in the form of a disk is placed at the port, or opening, of the open-ended cylinder
• small fraction of X-rays that are allowed to escape (1%) must pass through this filter

Question 26

What type of filter is used for X-ray machines operating below 70 kV?

Answer 26

1.5 mm of added aluminum filtration

Question 27

What type of filter is used for X-ray machines operating above 70 kV?

Answer 27

2.5 mm of added aluminum filtration

Question 28

Tubehead housing

Answer 28

• all structures within tube head are surrounded by a glass envelope in a vacuum environment.
• Glass envelope is housed by metal (lead)
• the metal insulates the tube head components and reduces the amount of radiation that can leak

Question 29

Oil

Answer 29

Within the tube head, the glass tube is immersed in oil to help absorb the heat created by x-ray production.

Question 30

Collimator

Answer 30

-disk of metal, usually lead, that has a small aperture that restricts the size or shape of the x-ray beam as it exits the tube head

Question 31

Collimation

Answer 31

the restriction of the x-ray beam size by a lead diaphragm

Question 32

Production of X-rays

Answer 32

1) The operator turns on the x-ray machine
2) the operator selects the kilo voltage and milliamperage setting, if appropriate. Many machines do not allow for such adjustments
3) The operator selects the exposure time. The exposure time is the length of time the X-rays are actually produced. In dental units, this time is usually less than 1 second.
4) The operator pushes the exposure button.
5) Electrical current passing through the filament boils off electrons through thermionic emission.
6) The potential difference between the cathode and the anode of the tube is activated. The electrons, which have a negative charge, are attracted to the positive anode at extremely high speeds. Nothing impedes their progress because the x-ray tube is a vacuum tube; there are no air molecules inside it.
7) The electrons from the filament collide with the target at the anode end of the tube. The collision of the high-speed electrons against the target process energy in the form of x-rays.
8) X-rays are generated in all directions (360 degrees) from the target. The X-rays travel at the speed of light.
9) Most of the X-rays produces are absorbed by the leaded glass x-ray tube and the metal housing surrounding the X-ray tube.
10) A small portion of the X-rays generated escape the x-ray tube through an unleaded area in the glass (the window).
11) These escaped X-rays then pass through a filter, which absorbs the less useful, lower energy X-rays in the beam.
12) The x-ray beam then passes through a lead collimator, which restricts the spread of the beam. The X-rays that pass through the opening in the collimator (the port) travel through the X-ray cone to reach the patient and the image receptor.