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Physics of Radiation Flashcards

1
Q

Wilhelm Roentgen

A

discovered radiation in 1895

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2
Q

How did Roentgen discover radiation?

A

He:
- created a vacuum tube, electrical current, and screens; noticed the green lights coming from the screen and named those rays “x-rays” (with “x” as the symbol for the unknown)
- demonstrated that shadowed images can be recorded permanently on photographic plates by placing objects between the tube and the plate
- exposed his wife’s hand for 15 minutes and saw the appearance of bones. This image is considered the first radiograph of the human body (you could see her ring as well)

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3
Q

Otto Walkhoff

A

created the first dental radiograph in 1895

  • placed a glass photographic plate in his mouth and exposed himself for 25 minutes
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4
Q

Edmund Kells

A

created the first practical radiograph in dentistry in 1896

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5
Q

Atom

A

Smallest component of an element

  • Consists of a nucleus and orbiting electron(s)
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6
Q

Molecule

A

two or more atoms combined

  • molecule is the smallest particle of substance that retains the property of the original substance
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7
Q

Nucleus

A

Positively-charged central core of an atom consisting of protons and neutrons

Contains nearly all of the atom’s mass

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8
Q

Protons

A

+ charge

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9
Q

Neutrons

A

no electrical charge

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10
Q

Electrons

A

(-) charge

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11
Q

Orbiting shells

A

three-dimensional structures around the nucleus that contain electrons

each shell can contain only a specific number of electrons

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12
Q

Shells are designated to which capital letters?

A

KLMNOPQ

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13
Q

The closer the orbit is to the nucleus, the — its binding energy (stronger bond)

A

Higher

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14
Q

What letter shell interaction has the highest binding energy and is the most useful for medical imaging?

A

K Shell

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15
Q

In order to remove an orbital electron from its shell?

A

the energy equal to or greater than the binding energy of a specific shell is needed

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16
Q

Radiation

A

propagation of energy through space in the form of particles or waves

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17
Q

T/F: Any exposure, no matter how small, doesn’t have the potential to cause harm

A

False, it does

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18
Q

Ionization

A

process by which an atom gains or loses electrons to become a negatively- or positively-charged atom

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19
Q

Ion

A

charged particle that is either positive or negative

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20
Q

Ion pair

A

positive ion (atom missing an electron) and a negative ion (ejected electron)

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21
Q

Ionizing radiation

A

any type of radiation that is high in energy and is capable of producing ions

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22
Q

What type of radiations are formed because of an ionizing process?

A

Particulate and electromagnetic radiation

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23
Q

Particulate radiation

A

involves particles that have a mass and travel in straight lines at high speeds

may have a charge, except for neutrons

include neutrons, protons, electrons, Beta particles, and Gamma particles

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24
Q

Can particulate radiation reach the speed of light?

A

No

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25
Electromagnetic radiation
electric and magnetic fields of energy that move through space in a *wave-like motion* includes radio waves, microwaves, visible light, UV rays, x-rays, and gamma rays (from low to high energy)
26
Only high energy waves have?
Ionizing capacity
27
X rays
powerful invisible rays that are capable of penetrating substances travels at the speed of light and has no mass or charge
28
Wavelength
distance between the peaks or crests of one wave to another (measured in *horizontal* length) determines the *energy* of the radiation
29
Longer wavelength
low frequency has *less* energy and thus *less* ability to penetrate objects
30
Shorter wavelength
high frequency has *more* energy and *more* ability to penetrate objects
31
X-ray Characteristics
Invisible No mass or weight No electrical charge Travel at the speed of light Travel in a wave-like motion Short wavelength of high frequency Cause ionization Can produce images Can cause biological changes in cells
32
what is first in the sequence of x-ray production?
An electrical current travels through the step-down transformer to the cathode and reduces the voltage from 110/220 to 3-5 volts
33
what is second in the sequence of x-ray production?
Filament is heated when the switch is activated
34
what is third in the sequence of x-ray production?
At the cathode, an electron cloud forms around the molybdenum cup by thermionic emission
35
what is fourth in the sequence of x-ray production?
Electrons are expelled at a high speed toward the anode’s focal spot within the tungsten target
36
what is fifth in the sequence of x-ray production?
Electrons hit the tungsten target at the anode and transform kinetic energy into x-rays. When the electrons hit the tungsten target, heat is formed, but it is dissipated through the copper stem.
37
Bremsstrahlung (braking) radiation
Major source (primary kind) of x-rays produced in dentistry (70%) Results when high-energy electrons come *close to the nuclei* of the tungsten atoms. The electrons move towards the nucleus (since they have opposite charges) and then *slow down* (this is why the name “braking” is used). When the electrons brake, energy is released (photons)
38
Characteristic radiation
Electrons from the cathode dislodge electrons from the inner orbital K/L shell of the tungsten atoms. When the electrons of the inner shells are dislodged, electrons from other orbits fill the empty space left by the ejected electron. During this process, energy is produced. Not as significant a source of x-rays as braking radiation.
39
After the x-rays leave the tube, they interact with?
any structure that is in the path of the x-rays ## Footnote Depending on the interaction between the x-rays and matter, different names are given
40
Compton scatter
Responsible for most of the interactions with matter in dental x-rays (around 60%)
41
What is the outcome of a compton scatter?
A photon interacts with an outer shell electron of a matter. The photon loses energy but continues to travel, and the electron is ejected. It is always easier to hit the** outer shells** than it is to hit the inner shells because the outer shell is bigger and contains more electrons
42
Photoelectric scatter
Responsible for about 30% of the interactions with matter in dental x-rays
43
what happens during a photelectric scatter?
* A photon interacts with an **inner shell electron** * The photon is absorbed and the electron is ejected * Ionization occurs ## Footnote less common
44
coherent (thompson) scatter
Responsible for about 8% of the interactions with matter in dental x-rays
45
what happens during a coherent scatter?
* Photons interact with an outer shell electron but the matter is **not** altered * Photons continue to travel with no loss of energy. * Ionization does not occur
46
No interaction (with object)
* Photons pass through the atom **unchanged** (dodging the bullets). * Produces **densities** in dental radiographs. If all photons passed through matter (patient) and reach the receptor, the image will be fully exposed (dark)
47
Primary radiation (X-rays)
Photons (bundle of energy) leave the x-ray tube as **primary radiation** (photons have not interacted with the patient’s body or any other objects)
48
Secondary (scatter) radiation
Created because primary beams are interacting with an object (matter) such as the patient’s oral structures (i.e., the x-rays that contacts the tooth creates secondary radiation) * Not useful for producing diagnostic quality images * creates **fog**
49
Is secondary radiation more or less penetrating than primary?
less, because it usually has longer wavelengths
50
Radiolucent areas
dark areas Produced by less dense structures that permit the passage of x-rays ## Footnote e.g., cysts, air spaces, soft tissues, tooth decay, dental pulp
51
Radiopaque areas
light areas Produced by denser structures that obstruct the passage of x-rays ## Footnote e.g., lamina dura (part of the bone around the roots that is dense), restorations, enamel, implants
52
Quality
* Describes the energy or penetrating ability of the x-ray beam * Controlled by kilovoltage * Higher kVp produces more penetrating x-rays than lower kVp * Higher kVp (80-100) is used for denser areas such as molars
53
Quantity
* Describes the number of x-rays produced * Controlled by ampere (A): the number of electrons that flow through the cathode * 1 milliampere (mA) = 1/1000 ampere. A dental radiograph operates in very small amounts of amperes, and therefore the unit used in dentistry is mA * Generally, 7-15 mA is required. Settings above 15 mA are not recommended as this can cause excessive heating
54
Intensity
Total energy contained in the beam Affected by **mA, kVp, distance**, and **exposure time**
55
To **increase** the intenstity of the beam:
**Increase** mA, kVp, and time **Decrease** the distance
56
To **decrease** the intenstity of the beam:
**Decrease** mA, kVp, and time **Increase** the distance
57
Half-value layer
Thickness of aluminum filters that reduces the intensity of the beam by half The filters remove less penetrating, longer wavelengths
58
Inverse square law
theory that radiation intensity is **inversely proportional** to the square of the distance from the source of radiation
59
To calculate the radiation density:
* Step 1: note how much shorter or longer the distance is (2 times farther → write 2, 3 times shorter → write 3) * Step 2: square the number (2 times farther or shorter → 2 squared = 4; 3 times farther or shorter → 3 squared = 9) * **Invert the number only if the source is farther **(2 times farther → 4 → ¼, this means the beam is ¼ intense) (3 times shorter → 9 → do not invert, this means the beam is 9 times more intense) * If cone length changed from 8 to 16 inches, how did the intensity change? 2 times further → 2, 2 squared = 4, therefore further invert = ¼. Reduced by 4 times, or ¼ the original intensity.
60
Density
Overall darkness of a radiographic image **Proportional** to mA, kVp, and exposure time
61
Milliampere-seconds (mA-s)
combination of milliamperes and seconds
62
To maintain similar density:
If time is **increased**, mA must be **decreased** If time is **decreased**, mA must be **increased** 15mA, 90kVp, 10 sec is changed to 10mA, 90 kVp.
63
To keep the same density, how long should the exposure be?
15 seconds
64
When is density decreased?
if the target structure is dense
65
Contrast
the difference between the lighter and darker shades of gray on a radiograph dependent on kVp
66
What results in many shades of **gray**?
increased kVp (long-scale contrast, low contrast) * Best for detecting **bone abnormalities**
67
What results in more **black and white** areas?
decreased kVp (short-scale contrast, high contrast) * Best for detecting **caries**
68
Sharpness
Capacity to produce details and distinct outlines
69
Penumbra
blurring at the edges of a structure on a radiograph
70
Sharpness can be increased when:
* Tungsten target of anode (focal spot) is **small** * Object to receptor distance is **short** * Tube (target) to receptor distance is **long**
71
What are the most important reasons for fuzziness?
Patient and tube head movements
72
Distortion
Variation of size and shape of the actual object
73
Magnification
enlargement of the object
74
Increased tube (target) to receptor distance allows?
more **parallel** rays and produces **less** magnification
75
Object to receptor distance:
**shorter** distance produces **less magnification**
76
Overlap
caused by improper **horizontal** angulation
77
Elongation and foreshortening are caused by?
improper vertical angulation
78
Elongation
caused by underangulation * Increase angulation to correct the error
79
Foreshortening
caused by overangulation * Decrease angulation to correct the error
80
In paralleling technique, the receptor and long axis of the tooth must be?
**parallel** to each other to prevent distortion

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